The cell reproduced and the organism grew.
In every cell of your body except your red blood cells exists a copy of your DNA.
In 1902, an American named Walter Sutton noticed that chromosomes duplicated themselves before cells divided so that each new cell had a full copy of the chromosomes.
I tried to call you on your cell phone, but I didn't get an answer.
We were startled by the ring of my cell phone.
My cell phone alerted me to a message.
Nervously, I dialed her cell and felt a flood of relief when she picked up.
Before I could respond, my cell phone played a Chopin etude.
I fished his cell number out of my pocket and dialed.
This one guy, I was his cell mate for a few months about the middle of my stretch; he was plain different.
If you're in a hurry connect to the cafe's modern online ordering system via your laptop or cell phone.
You have my purse and cell phone.
I had related to the detective what I'd learned from Willard Humphries, Grasso's cell mate, that he had a hide out somewhere away from Santa Barbara.
Back in your cell.
It was my cell phone!
From Betsy's cell phone?
He tossed the cell on the side of the road.
I know the motel where they are staying so the cell phone I've already discarded wasn't necessary.
The possibility of escape was nil so secure was our twelve foot square cell.
After an hour-long attempt to expel his wired energy, he returned to his room to the sound of his cell phone ringing.
"I found a cell phone!" another shouted as he scoured the gutters around the church.
His cell phone rang.
Hands shaking, she looked around the car's interior for a cell.
There was an old-school cell phone in the glove box.
The bump jarred the cell phone loose, and it fell in the space between the seat and door.
A shadow crossed her screen, and she snapped the cell against her body.
Surprised, Dusty turned to see Darian pull his cell from a pocket.
She squeezed the steering wheel then reached into her coat pocket for her cell phone.
Her replacement cell phone rang, jarring her.
Let's see if you can make it through the month, he said and dropped the cell.
She retrieved her cell and tucked the paper into her pocket.
Someone careened into her as she pried her cell from her pocket.
Her cell rang, and she recognized her doctor's number.
In the distance, she heard her cell phone ring.
He pulled out his cell to text his confidants.
Jake slid into the passenger seat beside her, pulling out his cell as he did.
Damian turned the cell phone back on and emerged into the warm evening air from the Marriott's conference room, the random place chosen by his spy chief for this week's intelligence briefing.
His cell rang before it could upload the number of voicemails and texts.
Any cell phone intercepts on why he's in town?
She didn't see Damian until afternoon, when he strolled into the library from sparring, ear to a cell phone.
His cell rang, and he answered, eyes always moving.
Sofia fingered the cell phone and credit card Damian thrust into her hands on her way out the door.
He strode beside her, whipping out his cell as they headed toward the nearest exit.
She pulled out the cell he'd given her and called the only number in it.
He hung up, and she stared at the cell then looked to her car.
Two went to Damian's cell and opened the door.
Pierre tossed her a familiar cell phone as they entered the mansion.
There were no clocks and she had no cell phone.
She suggested he take the cell phone but then remembered it was useless in the high mountains.
Dean left the cell confident that the old man was coping, but he was beginning to mirror Fred's concern with his past.
Both men were just as happy to have the quiet of the jail cell so they could talk in private.
As Dean left the building, the jailer sauntered back to Fred's cell.
As she opened the oven door to put the chicken in, her cell phone rang.
Extracting the cell phone from its sheath, she dialed Alex.
In that moment, she squirmed from his hands and screamed again, scrambling to reach the cell phone on the floor.
She grabbed her cell phone from the floor and dialed 911.
She turned as an officer shoved a cell phone at her.
If it couldn't wait, they would have called me on my cell phone.
She pulled up Dr. Wynn's office number on her cell, tempted to invite him to the beach this weekend instead of Logan.
Tamer pulled out his cell phone and scowled.
Deidre dug through her purse as she walked and pulled out her cell, thrilled to see she had battery power.
You have my cell number?
She put her cell phone on its charger and explored the house, admiring his taste in everything from furniture to paintings to simple décor.
He went to the only portal that glowed black --the portal to Hell --and stepped from the shadow world into the tiny, dark cell holding his friend.
He'd been fevered for a zillion years, trapped in the tiny cell in ever-changing forms, always in darkness.
He would stay in this holding cell on the outskirts of Hell until Sasha figured out some new grueling punishment.
One wall of his cell lit up suddenly.
He shielded his eyes and gazed into an empty prison cell opposite his.
Surprised, he crossed to the bars of his cell but found the whole wall disappeared when he touched it.
"You wouldn't happen to have a key to my cell, would you?" he asked.
Or I'll end up in the cell beside you.
Her cell phone had no signal, her head throbbed, and the coffee pot was empty.
Her cell rang, and she stared at it briefly through bleary eyes.
Rhyn tested the bonds of his cell again until a mage in a brown robe hurried down the hall to repair the damage.
Sometimes he could see out into the hallway and the empty cell across from his; sometimes he couldn't.
Today, the cell across from his wasn't empty.
Rhyn stretched out on the ground of his cell to stare at the ceiling.
She fingered the small teal evening purse hanging around her wrist, where her cell phone was.
The cell block fell silent, and he sensed the others also smelled the human blood.
The cowering healer left his corner of the cell for the first time in a while and approached the human on the bed.
She awoke on the lower bunk bed in a prison cell with no windows and a tiny metal toilet and sink.
She looked out of the front of the cell into a small corridor with equally harsh lighting.
Across from them was another cell, this one darkened.
The cell wall buckled and bent.
She scrambled toward the back of the cell, huddling with Lankha in a corner.
A man in a robe hurried down the hall as the beast battered itself against the weakening cell.
The cell repaired itself until it stood straight again.
The voice came from a cell down the hall.
She moved to the bars at the front of her cell, aware of the beast across the hall doing the same with a growl.
She stared with surprise at the low growl from the darkened cell across from her.
The sounds of Rhyn slamming his body into his cell and snarling awoke her sometime later.
The bars of her cell dissipated at his command, and she stepped into the hall.
The pale man was tall and lean, and he hung his hands again through the bars of his cell.
She closed her eyes, telling herself she'd survive this and figure out how to get the hell out of there, even if it meant bartering with the monsters on her cell block.
He slapped the wall of his cell, cursing Death again for not freeing him.
Jared exclaimed, hanging his hands through the bars in his cell.
It's the human you threw in the cell across from me, isn't it?
And to spend more time outside his cell.
He'd still rather be humoring Sasha and eating his oranges than sitting in the damned cell!
He took his time going back to the cell block.
He retreated to his cell and sat against the wall again, troubled by a familiar feeling of helplessness.
In the darkness of his cell, he admitted this was true, but he also knew no one could've saved his brother but him.
He slammed himself against the cell walls, roaring.
Rhyn made a racket in his cell.
Lankha was asleep above, and the clamoring of the cell block was gone.
Her eyes fell to the dark cell holding Rhyn.
His hands appeared through the cell bars.
Rhyn smashed himself against the cell, as if to prove his strength.
She sat next to the bars on her cell.
She glanced toward the dark cell and saw the silver eyes flash dangerously.
Rhyn smashed his cell hard enough for the walls to shudder.
When he stopped at her cell, she sighed.
As she emerged, both of them jumped back as Rhyn smashed into his cell.
They began beating against their cell walls, and the lights flickered again.
She eyed the door at the end of the hall, then her cell, and turned 360.
She'd lived through too much the past few days to be eaten by some boogeyman in a dark cell!
"Here ye go," the old man said, handing her a cell phone.
She dressed quickly to avoid comments on either her collar or her scars and flung herself into her bunk, reminded of her cell with Lankha.
She didn.t remember him being so tall in Hell, but she.d been afraid to look too hard at him when she passed his cell.
"I know where to find one," Rhyn said, his thoughts going to the Ancient healer that had been a prisoner in Sasha.s zoo in Hell across the hall from his own cell.
She.d last seen him in Hell, where they shared a cell together.
I think sometimes I should.ve moved into the cell beside yours in Hell.
Her translator had been lost during restless sleep then crushed in her pacing, and the cell was littered with several dozen pieces of colorful clothing.
When Ne'Rin signaled all was ready, he strode from the deck into the corridor and straight to her cell.
The cell where she sat measured six by six with a grey bench.
The 'holding cell' was a lavishly appointed 700 square foot room.
The human had spent most of the evening pacing around the cell, trying to make some sense of everything, stopping only briefly to eat, in an effort to soak up all the alcohol.
Her cell phone rang.
Lucky for them, Jackson's cell rang.
Connor's description of being in the holding cell 'losing his mind and living a nightmare' accurately described his feelings.
He took her to the holding cell.
Elisabeth stared straight ahead, then picked up her cell phone and walked out of the kitchen.
They walked in silence to the holding cell.
He slunk down to the holding cell to face the music.
Okay, let me give you my cell number.
The three sat in the kitchenette of the holding cell since Sarah refused to leave Connor, even for a minute.
He found Sarah and Connor on the sofa in the holding cell.
Maybe you could just give me her cell number.
Only the two gran it will take to put the lines down this way, and cell phone reception is unreliable.
Toby huddled against the black stone wall of his cell in Hell.
Ully called from the cell across the narrow hallway.
Toby looked up as the familiar demon named Jared passed his cell, trailed by two demons carrying a body with another familiar face.
"Gabriel!" he exclaimed, bounding to his cell door.
His long time friend, the assassin, was bloodied and unconscious. The demons tossed Gabriel's body into a dark cell two down from Ully's before they left.
I have more freedom than you when I'm not in this cell.
He gripped the bars of his cell and pressed his face against them, trying to see into the neighboring cells.
Gabriel's furious curse made Toby jump. Toby looked his direction the best he could through the bars of his cell and saw the walls around the dark cell shake.
Rhyn awoke from the island dreamscape in the shadow world. He rose, uncertain what happened but recalling his urgency. He crossed through the glowing black portal into the one place he'd hoped never to see again: Hell. Unwilling to get stuck in the cell where he'd spent many lifetimes, he chose to open the portal into the office of the Council's betrayer, Sasha. The office was as he remembered it, down to the black flames in the hearth.
He motioned dismissively towards the cell block.
Rhyn considered how he might use the demon, as he had once before. He didn't answer, pushing the door open to the cell block. Nearly all the cells were empty. "Where is everyone?" he asked.
"Not in the slightest. You put Gabe in my old cell," he said, stopping in front of it.
Rhyn stopped in front of Toby's cell and saw the young angel bouncing around.
"Oh, thank gods," Ully said from the cell across from Toby.
Rhyn stepped closer to his old cell, hating it and the fact his friend was trapped in it.
"You can't go after Death," Gabe said quietly as he stepped from the cell. The death-dealer was more unkempt than Rhyn had ever seen him.
Rhyn stopped in front of the dejected angel's cell.
"Hannah," Ully said and motioned to a cell farther down.
Toby asked, pressing his face against the cell door.
Rhyn left the cell block to Toby's protests and walked with Gabe through the antechamber and into the hallway on the other side. Gabe's gaze was dark, his air brooding. Rhyn opened a portal, and they crossed through to Gabe's cabin in the underworld.
Baffled, Toby shrugged and moved to the bars of his cell, looking to Ully for help. Ully rolled his eyes.
Toby felt almost as distraught at having to stay in the cell while his human was lost in the underworld. Not that he didn't trust Rhyn or Gabe, just that, he might be able to find her first.
As Toby watched, Ully stuck his hand out of the cell and placed it on the wall.
His cell door clicked open. Toby bounced to his feet.
Ully returned a couple of minutes later. He strode to Toby's cell and dangled the talisman before it. Toby's door opened.
Toby stepped out of the cell and closed it.
Rhyn opened the door, surprised to find the jailer's room empty. He'd expected Jared at least. He closed the door quietly behind him. He snatched the talisman hanging near the door, the one that freed inmates from their cells. He ignored the quickening of his pulse as he entered the familiar cell block.
He heard Hannah crying and smelled the unmistakable scent of human blood before he took a step onto the block. He strode down the block and paused in front of Hannah's cell. She was curled up on the bed, sobbing. When he looked at the cell across from her, he saw why. Jared stood in the cell, covered in blood. The cell looked as if a human had exploded, and Rhyn saw a pile of bones Jared had gnawed clean then stacked neatly.
He placed the talisman on the door frame of Hannah's cell. The door opened.
Rhyn ignored the demon and left the cell block, returning to the hallway before opening a portal. He crossed through the shadow world to the beach of the Caribbean Sanctuary. Toby was dragging Kiki up the beach by one leg.
Do you have your cell phone?
I'm not used to having a phone in the house, much less carrying a cell phone.
Her cell phone was in her pocket, but Alex probably figured she didn't have it with her.
Do you have your cell phone with you?
Turn your cell phone on and ignore the land line.
After she hung up, she made sure her cell phone was on and then headed for the kitchen.
It was like a prisoner's cell in some medieval castle.
He pulled the cell phone from its pouch on his pocket and flipped it open.
Carmen had only taken a few bites before the telephone rang – a reminder that her cell phone was in her room.
In her room, Carmen picked up her cell phone.
She pulled the cell phone out of her purse.
Once again he had been unable to reach her on the cell phone – for whatever reason.
I wish you would make an effort to be available on your cell phone when we're apart.
A cell phone was an advantage for others, and one more thing to keep track of for her.
It had a strap over the top to keep the cell phone from falling out.
She touched the pouch on her side, confirming that the cell phone was there.
Later that evening, Alex answered his cell phone.
The last thing she did before she left was make sure her cell phone was charged and turned on.
The worst part was the fact that the cell phone tower in their area was out.
She took her time getting home, ignoring her cell phone when it rang.
He was probably upset that she didn't answer her cell phone, but he had given her strict orders not to use it when she was driving.
She had forgotten her cell phone on the dresser again.
Keep your cell phone handy.
Ten O'clock found her hanging over the telephone, her cell phone on her hip.
Finally, at ten minutes after twelve, her cell phone rang.
She threw her cell phone on the bed.
If she hadn't thrown her cell phone on the bed, she could have called him.
Can I borrow your cell? she asked.
Sofi had taught him to use his cell phone and Dusty had taught him the computer.
She pocketed the cell, grateful for his consideration.
Jenn scoured their cell.
There were no weaknesses to the cell.
Sofi appeared relaxed in the cell, her head resting against the wall and her brilliant eyes focused on Jenn.
In order to find her, the first guardsmen would have to enter the cell.
Another fell, and the third shoved her into the cell.
She strained to keep her hold on the guardsman, even as the other one left the cell and snatched a sword to finish her off.
Returning to the cell, she used the long-sleeved shirt to wipe the blood off her body quickly and then to clean the blades of the weapons she snatched off the ground.
The heavy, musty scent of earth was contained within a four-by-four-foot cell, not even large enough for him to lie down.
Sirian paced a small underground cell beside the one Taran had occupied his first night in the city.
Before she fell again for Sirian's lies, she pushed the lever to seal his cell and walked away, rage and confusion making her head spin.
The iron wall was open in front of Sirian's cell.
The cell holding Sirian was closed.
"The more I think, the worse your plan," Vara grunted from the opened cell.
Hilden caught up to them as they reached the dungeon, where Vara was opening the iron door to the cell containing Sirian.
Memon ignored him, darting into the cell where the unconscious Rissa lay.
Vara hurried to close the iron door while Hilden rushed to the cell holding Memon.
Vara pulled her body towards him until she cleared the cell then lifted her.
Both cell doors had exploded off the cells and lay crumpled across the room.
Memon's lifeless body was wedged between the bars of one cell.
I gave him your cell phone number.
Their lovemaking lasted only a few minutes before his cell phone rang.
What about this cell phone thing with Jonathan?
Did you know Jonathan told our twins that Alex wants to get him a cell phone but you're being a … unreasonable about it?
Jonathan had reached puberty in full rebellion, which was one of the reasons she didn't think he should have a cell phone.
Fortunately Morino saw the ad for Apple Hors Devours in the local paper and recognized Alfonso's cell phone number before they made their first sale.
Alfonso lost the use of his cell phone for a month and Alex grounded Jonathan for the same amount of time.
That evening at home they were eating supper when Jonathan again asked Alex if he could get a cell phone.
They had badgered the parents of their thirteen year old member into getting him a cell phone and then had started on Carmen.
Later Carmen and Alex had explained to Jonathan that he was too young for the responsibility of a cell phone.
Pulling the cell phone from the holster on her side, she called Felipa.
Alex would be upset, but even worse; it would give Jonathan ammunition in his battle for a cell phone.
Remembering her cell phone, she reached for it.
She might as well figure on getting that cell phone for Jonathan.
Monday morning while Felipa took the men riding and the children were coloring, Carmen used her new cell phone to call the employment office.
If I had a cell phone, I could call you when I was ready.
Her cell phone rang at the exact time she was certain that her head would burst.
Pulling the cell phone from her purse, she tried calling Mr. O'Hara.
Apparently the area where the cabin sat was a dead spot for cell phones.
Another cell could develop at any time and this could start again all over.
This time her cell phone worked and a deep voice answered.
Once again she tried the cell phone, with the same results.
Brandon shoved a hand between the cushions and fished out the cell.
Brandon peppered her with questions, until she finally gave him her cell and let him listen to the messages.
She held up her cell.
An iPad in a bright green case and a cell phone labeled work phone!!!!! was sitting on the table in the informal dining area, a sticky note on it.
Rule five, keep your cell on.
The work cell rang, and she picked it up, answering instinctively.
I'll give you my cell number.
When you feel like venting, call, Gerry said and picked up her cell.
She fished the cell out of her purse and frowned.
Suddenly, she smiled and grabbed her cell phone.
I GPS tagged my cousins' cell phones and wallets.
Yeah. Only it wasn't just your cell and wallet.
A text drew her attention to the cell phone.
Xander tossed him the cell, and Darian strode out of the barn.
Making sure she's not sneaking up behind me to kill me, Xander said and removed his cell from his jeans.
Several were in Southern California while two blue dots – the one in her cell phone and the other in a shoe – appeared on the map in Texas.
Heart pounding hard, she sat on the bed and pulled out her cell phone.
"Take these somewhere far from here," Jonny told the vamp, handing over the shoes and cell.
Ashley wasn't in the room, though Jessi recognized some of her cousin's things: a pink cell phone charger, a backpack that yawned open to reveal clothes, the stack of colorful beaded bracelets on the arm of the couch.
He took Jessi's arm then whipped out his cell with his free hand.
No cell phone activity on either Jessi or her cousin.
Thenard stated that yeast was the cause of fermentation, and held it to be of an animal nature, since it contained nitrogen and yielded ammonia on distillation, nor was it conclusively proved that the yeast cell was the originator of fermentation until the researches of C. Cagniard de la Tour, T.
Traube (1858), the active cause of fermentation is due to the action of different enzymes contained in yeast and not to the yeast cell itself.
He agreed with Pasteur that the presence of living cells is essential to the transformation of sugar into alcohol, but dissented from the view that the process occurs within the cell.
This investigator held that the decomposition of the sugar molecules takes place outside the cell wall.
This body is being continually formed in the yeast cell, and decomposes the sugar which has diffused into the cell.
In this respect the plasma behaves in a similar manner towards the sugars as does the living yeast cell.
He emphasized the opinion that yeast derived from one cell was of no good for top fermentation, and advocated Pasteur's method of purification.
In the United Kingdom the employment of brewery yeasts selected from a single cell has not come into general use; it may probably be accounted for in a great measure by conservatism and the wrong application of Hansen's theories.
The flasks were then well shaken, and the yeast cell or cells settled to the bottom, and gave rise to a separate yeast speck.
To obtain an absolutely pure culture with certainty it is necessary, even when the gelatin method is employed, to start from a single cell.
Fermentation now includes all changes in organic compounds brought about by ferments elaborated in the living animal or vegetable cell.
In most cases four spores are formed within the cell by free formation.
In a monastery at Naples, near the cathedral of St Januarius, is still shown a cell in which he is said to have lived.
In some species (Ascaris decipiens) the giant cell is replaced by an irregular mass of protoplasm containing a number of small nuclei.
Each cell contains a zinc plate, immersed in a solution of zinc sulphate, and also a porous chamber containing crystals of copper sulphate and a copper plate.
The electromotive force of each cell is i 07 volts and the resistance 3 ohms. The Fuller bichromate battery consists of an outer jar containing a solution of bichromate of potash and sulphuric acid, in which a plate of hard carbon is immersed; in the jar there is also a porous pot containing dilute sulphuric acid and a small quantity (2 oz.) of mercury, in which stands a stout zinc rod.
The electromotive force of each cell is 2.14 volts, and the resistance 4.
ohms. The Leclanche is of the ordinary type, and each cell has an electromotive force of I 64 volts and a resistance of 3 to 5 ohms (according to the size of the complete cell, of which there are three sizes in use).
The size of the accumulators employed varies from a cell capable of an output of 8 ampere-hours, to a size giving 750 ampere-hours.
in diameter, to a total resistance of zoo ohms. The actual current required to work the instrument is 3.3 milliamperes (equivalent approximately to the current given by 1 Daniell cell through 3300 ohms), but in practice a current of to milliamperes is allowed.
A totally reflecting prism placed inside the glass cylinder projects the light which penetrates the film upon a selenium cell situated at the end of the cylinder.
To eliminate the sluggish action of the selenium transmitter a selenium cell similar to that at the transmitting station is arranged at the receiving apparatus, and exposed to precisely similar variations of light, the arrangement being such that the lag of this cell counteracts the lag of the transmitting cell.
When such a tube is inserted in series with a single voltaic cell and galvanometer it is found that the resistance of the tube is nearly infinite, provided the filings are not too tightly squeezed.
On creating an electric spark or wave in the neighbourhood of the tube the resistance suddenly falls to a few ohms and the cell sends a current through it.
At the receiving station Marconi connected a single voltaic cell B 1 and a sensitive telegraphic relay R in series with his tube of metallic filings C, and interposed certain little coils called choking coils.
In series with the tube is placed a single voltaic cell and a telegraphic relay, and Marconi added certain coils placed across the spark contacts of the relay to prevent the local sparks affecting the coherer.
In later improvements the secondary circuit of this jigger was interrupted by a small condenser, and the terminals of the relay and local cell were connected to the plates of this condenser, whilst the sensitive tube was attached to the outer ends of the secondary circuit.
2 The tube provided with certain screw adjustments had a single cell and a telephone placed in series with it, and one end of the tube was connected to the earth and the other end to a receiving antenna.
This device was converted into an electric wave detector as follows :-The mercury-steel junction was acted upon by the electromotive force of a shunted single cell and a siphon recorder was inserted in series.
This increases the resistance of the electrolytic cell.
If, however, one electrode of this cell is connected to the earth and the other to a receiving antenna and electric waves allowed to fall on the antenna, the oscillations passing through the electrolytic cell will remove the polarization and L temporarily decrease the resistance of the cell.
Fessenden employed a simple fine loop of Wollaston platinum wire in series with a telephone and shunted voltaic cell, so that when electric oscillations passed through the fine wire its resistance was increased and the current through the telephone suddenly diminished (R.
The receiving arrangements comprised also an open or antenna circuit connected directly with a closed condenser-inductance circuit, but in place of the spark gap in the transmitter an electrolytic receiver was inserted, having in connexion with it as indicator a voltaic cell and telephone.
It is largely used for the purpose of making standard electric cells, such for example as the Weston cell.
4), in an early form, consisted of a cell of insulating material having at its bottom a flat-headed platinum screw G; on the top of G was a layer of carbon powder C, on the top of that a platinum disk D, and above that again, forming the cover of the cell, a disk of ivory B, held in position by a ring E.
5 He proposed to introduce into the circuit a cell containing carbon powder, the pressure on which could be varied by the micro- vibrations of a diaphragm.
He sometimes held the carbon powder against the diaphragm in a small tr ans' shallow cell (from a quarter to half an inch in diameter and about an eighth of an inch deep), and sometimes he used what he describes as a fluff, that is, a little brush of silk fibre with plumbago rubbed into it.
A large nematocyst, with everted thread, is seen in the right-hand ectodermal cell.
The cnidoblasts are the mother-cells of the nematocysts, each cell producing one nematocyst in its interior.
A further stage in evolution is that the muscle-cells lose their connexion with the epithelium and come to lie entirely beneath it, forming a sub-epithelial contractile layer, developed chiefly in the tentacles of the polyp. The of the evolution of the ganglioncells is probably similar; an epithelial cell develops processes of nervous nature from the base, which come into connexion with the bases of the sensory cells, with the muscular cells, and with the similar processes of other nerve-cells; next the nerve-cell loses its connexion with the outer epithelium and becomes a sub-epithelial ganglion-cell which is closely connected with the muscular layer, conveying stimuli from the sensory cells to the contractile elements.
The uppermost is a purely muscular cell from the sub-umbrella; the two lower are epidermo-muscular cells from the base of a tentacle; the upstanding nucleated portion forms part of the epidermal mosaic on the free surface of the body.
con, Concrement - cell with otolith.
If the germ-cells are undifferentiated, the offspring may arise from many cells or from a single cell; the first type is (4) germinal budding, the second is (5) sporogony.
The spore-cell multiplies by division, while the enveloping cell is nutrient and protective.
The spore cell gives rise to a " sporelarva," which is set free in the coelenteron and grows into a medusa.
In Hydra the odcyte is a large amoeboid cell, which sends out pseudopodia amongst the odgonia and absorbs nutriment from them.
The result of cleavage in all cases is a typical blastula, which when set free becomes oval and develops a flagellum to each cell, but when not set free, it remains spherical in form and has no flagella.
Thallophyta are the most lowly organized plants and include a great variety of forms, the vegetative portion of which consists of a single cell or a number of cells forming a more or less branched thallus.
The male gametophyte is represented by one or few cells and, except in a few primitive forms where the male cell still retains the motile character as in the Pteridophyta, is carried passively to the macrospore in a development of the pollen grain, the pollen tube.
After fertilization the female cell, now called the oospore, divides and part of it develops into the embryo (new sporophyte), which remains dormant for a time still protected by the ovule which has developed to become the seed.
The male gametophyte is sometimes represented by a transitory prothallial cell;, the two male cells are carried passively down into the ovary and into the mouth of the ovule by means of the pollen-tube.
The female gametophyte is extremely reduced; there is a sexual apparatus of naked cells, one of which is the egg-cell which, after fusion with a male cell, divides to form a large siispensorial cell and a terminal embryo.
The term Anatomy, originally employed in biological science to denote a description of the facts of structure revealed on cutting up an organism, whether with or without the aid of lenses for the purposes of magnification, is restricted in the present article, in accordance with a common modern use, to those facts of internal structure not concerned with the constitution of the individual cell, the structural unit of which the plant is composed.
An account of the structure of plants naturally begins with the cell which is the proximate unit of organic structure.
The cell is essentially an individualized mass of protoplasm containing a differentiated protoplasmic body, called a nucleus.
A, Cell (individual) of the unicellular Green Alga Pleurococcus, as an example of an undifferentiated autonomous assimilating cell.
The primitive cell sends colorless tubelets (rhizoids, rh.) into the mud on which it grows.
The basal cell has less chlorophyll than the others, and is expanded and fixed firmly to the rock on which the plant grows by the basal surface, rh, thus forming a rudimentary rhizoid.
In such cases the characters of the adult tissue clearly depend solely upon the characters of the cell-walls, and it is usual in plant-anatomy to speak of the wall with its enclosed cavity as the cell, and the contained protoplasm or other substances, if present, as cell-contents.
For a more detailed description of the cell see CYTOLOGY and the section on Cytology of Plants below).
L, Optical section of cell of parenchyma in the same moss.
Note thick walls and oblique slit-like pits with opposite inclination on the two sides of the cell seen in surface view.
U, Absorbing cell, with process (root-hair) from piliferous layer of root of Phanerogam.
Endodermal cell of Phanerogam, with suberized central band on radial and transverse walls.
In the Algae such a cell consists essentially of: (1) a mass of protoplasm provided with (2) a nucleus and (3) an assimilating apparatus consisting of a colored protoplasmic body, called a chromatophore, the pigment of which in the pure green forms is chlorophyll, and which may then be called a cliloroplast.
It is from such a living and assimilating cell, performing as it does all the vital functions of a green plant, that, according to current theory, all the different cell-forms of a higher plant have been differentiated in the course of descent.
The cells Cell and are commonly joined end to end in simple or branched Tissue filaments.
In the group of the Siphoneae both these types of differentiation may exist in the single, long, branched, tube-like and multinucleate cell (coenocyte) which here forms the plant-body.
In Caulerpa the imitation of a higher plant by the differentiation of fixing, supporting and assimilating organs (root, stem and leaf) from different branches of the single cell is strikingly complete.
Each branch grows simply by the transverse division of its apical cell.
The cells belonging to any given thread may be recognized at an early stage of growth, because each cell is connected with its neighbors belonging to the same thread by two depressions or pits, one at each end.
Many of the lower forms of Brown Seaweeds (Phoeophyceae) have a thallus consisting of simple or branched cell threads, as in the green and red forms. The lateral union of the branches to form a solid thallus is not, however, so common, nor is it carried to so high a pitch of elaboration as in the Rhodophyceae.
a solid mass of cells, formed by cell division in all directions of space.
In the Fucaceae, on the other hand, there is a single prismatic apical cell situated at the bottom of a groove at the growing apex of the thallus, which cuts off cells from its sides to add to the peripheral, and from its base to add to the central permanent cells.
The whole of the tissue of the plant is formed by the division of this apical cell.
In addition to the cell types described, it is a very common occurrence in these bulky forms for rhizoid-like branches of the cells to grow out, mostly from the cells at the periphery of the medulla, and grow down between the cells, strengthening the whole tissue, as in the Rhodophyceae.
the group, the exceptions being met with almost entirely among the higher Brown Seaweeds, in which is found parenchyma produced by the segmentation of an apical cell of the whole shoot, or by cell division in some other type of meristem.
It always consists of true parenchyma, and is entirely formed by the cutting off of segments from an apical cell.
The latter are plates of green tissue one cell thick, while the stem consists of uniform more or less elongated cylindrical cells.
The whole cavity of the cell is sometimes stuffed with proteid contents.
The end of the cell is slightly swollen, fitting on to the similar swollen end of the next leptoid of the row exactly after the fashion of a trumpet-hypha.
The leaf consists of a central midrib, several cells thick, and two wings, one cell thick.
The simplest type consists simply of a single elongated cell projecting above the general level of the lairs, epidermis.
The root-hair end~ blindly and is simply an outgrowth from a surface cell, havin~ no cross-walls.
The whole of the middle lamella or originally formed cell-wall separating one from another disappears before the adult state is reached, so that the walls of the hydroids consist of a framework of lignified bars, with open communication between the cell cavities.
leaf-gap; cor cell; per.
On germination of the seed the radicle first grows out, increasing in size as a whole, and soon adding to its tissues by cell division at its apical growing-point.
In most Pteridophytes there is a single large apical cell at the end of each stem and root axis.
In other cases, again, a group of two or four prismatIl cells takes the place of the apical cell.
Apical cell, p. Wall marking limit between the plerome k, initial segment of root-cap. P and the pleriblem Pb.
The periblem, one cell thick at the apex, produces the cortex, to which the piliferous layer belongs in Monocotyledons; and the plerome, which is nearly always sharply separated from the periblem, gives rise to the vascular cylinder.
A tissue mother-cell of the phloem may give rise to (i) a segment of a sieve-tube with its companion cell or cells; (2) a phloem fibre; (3) a single phloem-parenchyma (cambiform) cell, or a ve~rtical file of short parenchyma cells.
When a given initial cell of the cambium has once begun to produce cells of this sort it continues the process, so that a radial plate of parenchyma cells is formed stretching in one plane through the xylem and phloem.
The early histological researches of botanists led them to the recognition of the vegetable cell, and the leading writers in the middle of the ~9th century pointed out the probable identity of Von Mohls protopiarm with the sarcode of zoologists.
Very soon the single cell gives rise to a chain of cells, and this in.
turn to a cell mass, the individual units of which are at first quite uniform.
This is a primal necessity of the protoplast,and every cell gives evidence of its need by adopting one of the various ways in which such need is supplied.
The apparently structureless substance is saturated with it; and if once a cell is completely dried, even at a low temperature, in the enormous majority of cases its life iS gone and the restoration of water fails to enable it to recover.
The process involves the iqter-action of water also, and this, as we have seen, is always present in the cell.
But it is certain that it can only be present in a cell in very small amount at any moment, for an extremely dilute solution acts as a poison to protoplasm.
The formaldehyde at once undergoes a process of condensation oi- polymerization by the protoplasm of the plastid, while the hydrogen peroxide is said to be decomposed into water and free oxygen by another agency in the cell, of the nature of one of the enzymes of which we shall speak later.
As much sugar as is produced in excess of the immediate requirements of the cell is converted into the insoluble form of starch by the plastidsof the chlorophyll apparatus, and is so withdrawn from the sphere of action, thereby enabling the construction of further quantities of sugar to take place.
The presence of too much sugar in solution in the sap of the cell inhibits the activity of the chloroplasts; hence the necessity for its removal.
The idea of an identity of protoplasm does not involve a denial of special powers developed in it in different situations, and the possession of such a power by the vegetable cell is not more striking than the location of the powers of co-ordination and thought in the protoplasm of cells of the human brain.
The material and the energy go together, the decomposition of the one in the cell setting free the other, which is used at once in the vital processes of the cell, being in fact largely employed in constructing protoplasm or storing various products.
The supply of oxygen to a plant is thus seen to be as directly connected with the utilization of the energy of a cell as is that of food concerned in its nutrition.
In such cells as are capable of absorbing it, by virtue oi their chlorophyll apparatus, the greater part of it is converted int< the potential form, and by the transport from cell to cell of th compounds constructed every part of the plant is put into possessiol of the energy it needs.
the framework of the fabric of the cell, and the construction of a continuously increasing skeleton; part is used in maintaining the normal temperature of the~plant, part in constructing various substances which are met with in the interior, which serve various purposes in the working of the vital mechanism.
These include cell walls and the various stored products found in growing cells.
The growth of such a cell will be found to depend mainly upon five conditions: (I) There must be a supply of nutritive or plastic materials, at the expense of which the increase of its living substance can take place, and which supply the needed potential energy.
(2) There must be a supply of water to such an extent as to set up a certain hydrostatic pressure in the cell, for only turgid cells can grow.
(3) The supply of water must be associated with the formation of osmotic substances in the cell, or it cannot be made to enter it.
(4) The cell must have a certain temperature, for the activity of a protoplast is only possible within certain limits, which differ in the case of different plants.
(5) There must be a supply of oxygen to the growing cell, for the protoplast is dependent upon this gas for the performance of its vital functions, and particularly for the liberation of the energy which is demanded in the constructive processes.
This is evident from the consideration that the growth of the cells is attended by the growth in surface of the cell wall, and as the latter is a secretion from the protoplasm, such a decomposition cannot readily take place unless oxygen is admitted to it.
When these conditions are present, the course of the growth of a cell appears to be the following: The young cell, immediately it is cut off from its fellow, absorbs water, in consequence of the presence in it of osmotically active substances.
There is set up at once a certain hydrostatic pressure, due to the turgidity which ensues upon such absorption, and the extensible cell wall stretches, at first in all directions.
The growth or increase of the protoplasm at the expense of the nutritive matter for a time keeps pace with the increased size of the cell, but by and by it becomes vacuolated as more and more water is attracted into the interior.
The growth of the protoplasm, though considerable, is therefore not commensurate with the increase in the size of the cell.
The stretching of the cell wall by the hydrostatic pressure is fixed by a secretion of new particles and their deposition upon the original wall, which as it becomes slightly thicker is capable of still greater extension, much in the same way as a thick band of indiarubber is capable of undergoing greater stretching than a thin one.
The increase in surface of the cell wall is thus duefirstly to the stretching caused by turgidity, and secondly to the formation and deposition of new substance upon the old.
When the limit of extensibility is reached the cell wall increases in thickness from the continuation of the latter of the two processes.
The rate of growth of a cell varies gradually throughout its course; it begins slowly, increases to a maximum, and then becomes slower till it stops.
If we consider the be~aviour of a growing organ such as a root, we find that, like a cell, it shows a grand period, of growth.
This may possibly be the cell sap in their interior, which must exercise a slightly different hydrostatic pressure on the basal and, the lateral walls of the cells.
Many experiments point to certain small grains of starch which are capable of displacement as the position of the cell is altered.
The peculiarity of the protoplasm in almost every cell is that it is especially active in the regulation of its permeability by water.
It is the immediate cause of the phenomena of circumnutation, each cell of the circumnutating organ showing a rhythmic enlargement and decrease of its dimensions, due to the admission of more and less water into its interior.
Pythium in seedlingsor to a poison diffusing from cell to cell; in the case of unicellular plantse.g.
If a mass of living plant-tissue is cut, the first change observed is one of color: the white flesh of a potato or an apple turns biown as the air enters, and closer examination shows that cell walls and contents are alike affected.
Plcotrachelus causes the invaded Pilobolus to swell up, and changes the whole course of its cell metabolism, and similarly with Plasmodiophora in the roots of turnips, and many other cases.
If such a general parasite carries its activities farther, every cell may be killed and the plant forthwith destroyed e.g.
If the attack of a parasite is met by the formation of some substance in the protoplasm which is chemo- tactically repulsive to the invader, it may be totally incapable of penetrating the cell, even though equipped with a whole armoury of cytases, diastatic and other enzymes, and poisons which would easily overcome the more passive resistances offered by mere cell-walls and cell-contents of other plants, the protoplasm of which forms bodies chemotactically attractive to the Fungus.
But even when inside it does not follow that the Fungus can kill the cell, and many cases are known where the Fungus can break throtigh the cells first lines of defence (cell-wall and protoplasmic lining); but the struggle goes on at close quarters, and various degrees of hypertrophy, accumulation of plastic bodies or secretions, discolorations, &c.,, indicate the suffering of the still living cell.
Finally, cases occur where the invaded cell so adapts itself to the presence of the intruder that life in commonsymbiosisresults.
The elementary unit of plant structure, as of animal structure, is the cell.
The Cell Theory.For a general and historical account of the cell theory see CYTOLOGY.
It is sufficient to note here that cells were first of all discovered in various vegetable tissues by Robert Hooke in 1665 (Micrographia); Malpighi and Grew (1674-1682) gave the first clear indications of the importance of cells in the building up of plant tissues, but it was not until the beginning of the 19th century that any insight into the real nature of the cell and its functions was obtained.
The nucleus was definitely recognized in the plant cell by Robert Brown in 1831, but its presence had been previously indicated by various observers and it had been seen by Fontana in some animal cells as early as 1781.
The cell theory so far as it relates to plants was established by Schleiden in 1838.
He showed that all the organs of plants are built up of cells, that the plant embryo originates from a single cell, and that the physiological activities of the plant are dependent upon the individual activities of these vital units.
It is true that in the unicellular plants all the vital activities are performed by a single cell, but in the multicellular plants there is a more or less highly developed differentiation of physiological activity giving rise to different tissues or groups of cells, each with a special function.
The cell in such a division of labor cannot therefore be regarded as an independent unit.
General Structure and Differentiation of the Vegetable Cell.
The simplest cell forms are found in embryonic tissues, in.
The protoplasm of a living cell con.sists of a semifluid granular substance, called the cytoplasm, one or more nuclei, and sometimes centrosomes and plastids.
Very little is known of the finer structure of the cytoplasm of a vegetable cell.
The cytoplasm is largely concerned in the formation of spindle fibres and centrosomes, and such structures as the cell membrane, cilia, or flagella, the coenocentrum, nematoplasl~ or vibrioids and physodes are also products of its activity.
In other forms such as Elodea, Nitella, Chara, &c., where the cytoplasm is mainly restricted to the periphery of the sap vacuole and lining the cell wall, the streaming movement is exhibited in one direction only.
In some cases both the nucleus and the chromatophores may be carried along in the rotating stream, but in others, such as T.Titeila, the chloroplasts may remain motionless iii a non-motile layer of the cytoplasm in direct contact with the cell wall.i Desmids, Diatoms and Oscillaria show creeping movements probably due to the secretion of slime by the cells; the swarmspores and plasmodium of the Myxomycetes exhibit amoehoid movements; and the motile spores of Fungi and Algae, the spermatozoids of mosses, ferns, &c., move by means of delicate prolongations, cilia or flagella cf the protoplast.
They are spherical, oval, fusiform, or rod-like, and are always found in the cytoplasm, never in the cell-sap. They appear to be permanent organs of the cell, and are transmitted from one cell to another by division.
of the cell.
some plants of changing their position in the cell under the stimulus of a variation in the intensity of the light rays which fall upon them.
In the yeast cell it accumulates and disappears very rapidly according to the conditions of nutrition and is sometimes so abundant as to fill the cell almost entirely (Errera, 1882, 1895: Wager and Peniston, 1910).
The cell sap contains various substances in solution such as sugars, inulin, alkaloids, glucosides, organic acids and various inorganic salts.
It is probable that most, if not all, the metabolic changes which take place in a cell, such as the transformation of starch, proteids, sugar, cellulose; and the decomposition -of numerous other organic substances which would otherwise require a high temperature or powerful reagents is also due to their activity.
If it is absent, the cell loses its power of assimilation and growth, and soon dies.
HaberIandt has shown that in plant cells, when any new formation of membrane is to take place in a given spot, the nucleus is found in its immediate vicinity; and Klebs found that only that portion of the protoplasm of a cell which contains the nucleus is capable of forming a cell-wall; whilst Townsend has further shown that if the non-nucleated mass is connected by strands of protoplasm to the nucleated mass, either of the same cell or of a neighboring cell, it retains the power of forming a cell-membrane.
This has a strong attraction for basic aniline dyes, and can usually be distinguished from other parts of the cell which are more easily colored by acid anilines.
plants do not appear to be permanent organs of the cell.
In multinucleate cells the division of the nucleus is independent of the division of the cell.
It may also take place where rapid proliferation of the cell is going on, as in the budding of the Yeast plant.
The spindle figure is probably the expression of forces which are set up in the cell for the purpose of causing the separation of the daughter chromosomes.
Hartog has endeavoured to show that it can only he formed by a dual force, analagous to that of magnetism, the spindle-fibi es being comparable to the lines of force in a magnetic field and possibly due to electrical differences in the cell.
It is clear, however, that an equal quantitative division and distribution of the chromatin to the daughter cells is brought about; and if, as has been suggested, the chromatin consists of minute particles or units which are the carriers of the hereditary characteristics, the nuclear division also probably results in the equal division and distribution of one half of each of these units to each daughter cell.
The two divisions of the spore mother cell in which the reduction takes place, follow each other very rapidly and are known as Heterotype and Homotype (Flemming), or according to the terminology of Farmer and Moore (1905) as the meiotic phase.
Cell Division.With the exception of a few plants among the Thallophytes, which consist of a single multinucleate cell, Caulerpa, Vaucheria, &c., the division of the nucleus is followed by the division of the cell either at once, in uninucleate cells, or after a certain number of nuclear divisions, in multinucleate cells.
In the Thallophytes the cytoplasm may be segmented by constriction, due to the in-growth of a new cell wall from the old one, as in Spirogyra and Cladophora, or by the formation of cleavage furrows in which the new cell-wall is secreted, as occurs in the formation of the spores in many Algae and Fungi.
Cell budding takes place in yeast and in the formation of the conidia of Fungi.
In a few cases both among the higher and the lower plants, of which the formation of spores in the ascus is a typical example, new cells are formed by the aggregation of portions of the cytoplasm around the nuclei which become delimited from the rest of the cell iontents by a membrane.
This is known as free cell formation.
Cell Membrane.The membrane which surrounds the protoplasts in the majority of plants is typically composed of cellulose, together with a number of other substances which are known as pectic compounds.
These layers arc secreted by the protoplasm by the direct apposition of substances on those already in existence; and they may go on increasing in thickness, both by apposition and by the intussusception of particles probably carried in through the protoplasmic fibres, which penetrate the cell-wall as long as the cell lives.
Besides the internal or centripetal growth, some cell-walls are thickened on the outside, such as pollen grains, oospores of Fungi, cells of Peridineae, &c. This centrifugal growth must apparently take place by the activity of protoplasm external to the cell.
+h,r, 1)s~,~s-s Diatoms and Desmids, according to recent researches, the thickenings on the outer walls of the cells are due to the passage of protoplasm from the interior of the cell to the outside, through pores which are found perforating the wall on all sides.
fusing cells, the male cell FIG.
+1~ ii 1n a, Antipodal cell; sp, polar nuclei; eing e sma er.
cent; the male cell may be motile or non-motile.
In many of the Fungi the non-motile male cell or nucleus is carried by means of a fertilizing tube actually into the interior of the egg-cell, and is extruded through the apex in close proximity to the egg nucleus.
In the Florideae, Lichens and Laboulbenjaceae the, male cell is a non-motile spermatium, which is carried to the female organ.
In Monoblepliaris, one of the lower Fungi, in some Algae, in the Vascular Cryptograms, in Cycads (Zamia and Cycas), and in Ginkgo, an isolated genus of Gymnosperms, the male cell is a motile spermatozoid with two or more cilia.
In the Algae, such as Fucus, Volvox, Oedogonium, Bulbochaete, and in the Fungus Monoblepharis, the spermatozoid is a small oval or elongate cell containing nucleus, cytoplasm and sometimes plastids.
cell, which is non-motile, is carried to the oosphere by means of a pollen tube.
Belajeff regards it as a true centrosome; but this is doubtful, for while in some cases it appears to be connected with the division of the cell, in others it is independent of it.
The eggcell or oosphere is a large cell containing a single large nucleus, and in the green plants the rudiments of plastids.
In plants with multinucleate cells, such as Albugo, Peronospora and Vaucheria, it is usually a uninucleate cell differentiated by separation of the nuclei from a multinucleate cell, but in Albugo bliti it is multinucleate, and in Sphaero plea it may contain more than one nucleus.
The strongest direct evidence seems to be that the nuclear substances are the only parts of the cells which are always equivalent in quantity, and that in the higher plants and animals the male organ or spermatozoid is composed almost entirely of the nucleus, and that the male nucleus is carried into the female cell without a particle of cytoplasm.i Since, however, the nucleus of the female cell is always accompanied by a larger or smaller quantity of cytoplasm, and that in a large majority of the power plants and animals the male cell also contains cytoplasm, it cannot yet be definitely stated that the cytoplasm does not play some part in the process.
Boveri in fact has put forward the view that the chromosomes are elementary units which maintain an organic continuity and independent existence in the cell.
In the Cyanophyceae the contents of the cell are differentiated into a central colorless region, and a peripheral layer containing the chlorophyll and other coloring matters together with granules of a reserve substance called cyanophycin.
In the yeast cell the nucleus is represented by a homogenous granule, probably of a nucleolar nature, surrounded and perhaps to some extent impregnated by chromatin and closely connected with a vacuole which often has chromatin at its periphery, and contains one or more volutin granules which appear to consist of nucleic acid in combination with an unknown base.
The sieve tubes contain a thin lining layer of protoplasm on their walls, but no nuclei, and the cell sap contains albuminous substances which are coagulable by heat.
Protoplasmic Continuity.Except in the unicellular plants the cell is not an independent unit.
pit-threads and wail-threads may occur in the same cell, but more often the threads are limited to the pits.
v.; The Cell and some of its Constituent Structures, Science Progress (1897); Farmer and Moore, On the Melotic Phase in Animals and Plants, Quart.
ix.; The Genesis and Development of the Wall and Connecting Threads in the Plant Cell.
Hartog, The Dual Force of the Dividing Cell, Proc. Roy.
x.; The Cell Structure of the Cyanophyceae, Proc. Roy.
He took up his residence in Avila, where he had built a convent; and here he resumed the common life of a friar, leaving his cell in October 1497 to visit, at Salamanca, the dying infante, Don Juan, and to comfort the sovereigns in their parental distress.
The pupal stage is passed in an earthen cell, just beneath the surface of the ground.
All that do not happen to attach themselves to a bee of the genus Anthophora perish, but those that succeed in reaching the right host are carried to the nest, and as the bee lays an egg in the cell the triungulin slips off her body on to the egg, which floats on the surface of the honey.
The violent personalities of a pamphlet entitled Marie Joseph Chenier et le prince des critiques (1844), in reply to Jules Janin, brought him a six months' sojourn in La Pelagic, in the cell just quitted by Lamennais.
The setae ar ° invariably formed each within an epidermic cell, and they are sheathed in involutions of the epidermis.
Vezhdovsky's figures of Rhynchelmis agree with those of Bergh in showing the backward growth of the nephridium from the funnel cell.
Rarely the nephridium does not communicate with the coelom; in such cases the nephridium ends in a single cell, like the "flame cell" of a Platyhelminth worm, in which there is a lumen blocked at the coelomic end by a tuft of fine cilia projecting into the lumen.
In any case the nephridia which occupy the segments of the body generally are first of all represented by paired structures, the "pronephridia," in which the funnel is composed of but one cell, which is flagellate.
Each renal organ is a sac lined with glandular epithelium (ciliated cell, with concretions) communicating with the exterior by its papilla, and by ce, Cerebral ganglia.
Facing the castle, on the western side of the pill, stand the considerable remains of Monkton Priory, a Benediction house founded by Earl William Marshal as a cell to the abbey of Seez or Sayes in Normandy, but under Henry VI.
Further incursions made by the Danes in 998 and in 1015 under Canute probably resulted in the destruction of the priory, on the site of which a later house was founded in the 12th century as a cell of the Norman abbey of Lysa, and in the decayed condition of Wareham in 1086, when 203 houses were ruined or waste, the result of misfortune, poverty and fire.
- e,f, Owl moth (Heliothis armigera); a,b, egg, highly magnified; c, larva or caterpillar; d, pupa in earthen cell.
The change that is required to transform Exopterygota into Endopterygota is merely that a cell of hypodeimis should proliferate inwards instead of outwards, or that a minute hypodermal evaginated bud should be forced to the interior of the body by the pressure of a contracted cuticle.
Each fibre is formed by the outgrowth of a single epidermal cell of the testa or outer coat of the seed.
Thus during the six days of the week the Therapeutae "philosophized," each in his own cell, but on the Sabbath they met in a common assembly, where women also had places screened off from the men, and listened to a discourse from one who was the eldest and most skilled in their doctrines.
During his stay at Manresa, he lived for the most part in a cell at the Dominican convent; and here, evidently, he had severe illnesses.
Klaproth in 1799, is obtained when pure carbon (graphite or charcoal) is oxidized by alkaline permanganate, or when carbon forms the positive pole in an electrolytic cell (Ber., 1883, 16, p. 1209).
The converse is presented in the common electric cell.
Externally is a thin cuticle; this covers the epidermis, which consists of a syncytium with no cell limits.
Each cell measures 35 cub.
The most interesting room in the palace is Philip II.'s cell, from which through an opening in the wall he could see the celebration of mass while too ill to leave his bed.
Volta's cell consists essentially of two plates of different metals, such as zinc and copper, connected by an electrolyte such as a solution of salt or acid.
The electromotive force of Volta's simple cell falls off rapidly when the cell is used, and this phenomenon was shown to be due to the accumulation at the metal plates of the products of chemical changes in the cell itself.
Constant cells may be divided into two groups, according as their action is chemical (as in the bichromate cell, where the hydrogen is converted into water by an oxidizing agent placed in a porous pot round the carbon plate) or electrochemical (as in Daniell's cell, where a copper plate is surrounded by a solution of copper sulphate, and the hydrogen, instead of being liberated, replaces copper, which is deposited on the plate from the solution).
The reunited current was then led through another cell C, in which the strength of the current must be the sum of those in the arms A and B.
Faraday found that the mass of substance liberated at the electrodes in the cell C was equal to the sum of the masses liberated in the cells A and B.
of all these experiments may be summed up in the statement that the amount of chemical action is proportional to the quantity of electricity which passes through the cell.
He found that the amounts of the substances liberated in each cell were proportional to the chemical equivalent weights of those substances.
In order that the current should be maintained, and the electromotive force of the cell remain constant during action, it is necessary to ensure that the changes in the cell, chemical or other, which produce the current, should neither destroy the difference between the electrodes, nor coat either electrode with a non-conducting layer through which the current cannot pass.
As an example of a fairly constant cell we may take that of Daniell, which consists of the electrical arrangement - zinc zinc sulphate solution copper sulphate solution copper, - the two solutions being usually separated by a pot of porous earthenware.
When the zinc and copper plates are connected through a wire, a current flows, the conventionally positive electricity passing from copper to zinc in the wire and from zinc to copper in the cell.
Thus as long as a moderate current flows, the only variation in the cell is the appearance of zinc sulphate in the liquid on the copper side of the porous wall.
In spite of this appearance, however, while the supply of copper is maintained, copper, being more easily separated from the solution than zinc, is deposited alone at the cathode, and the cell remains constant.
Thus in the Daniell cell the dissolution of copper as well as of zinc would increase the loss in available energy.
Considered thermodynamically, voltaic cells must be divided into reversible and non-reversible systems. If the slow processes of diffusion be ignored, the Daniell cell already described may be taken as a type of a reversible cell.
Let an electromotive force exactly equal to that of the cell be applied to it in the reverse direction.
When the applied electromotive force is diminished by an infinitesimal amount, the cell produces a current in the usual direction, and the ordinary chemical changes occur.
If the external electromotive force exceed that of the cell by ever so little, a current flows in the opposite direction, and all the former chemical changes are reversed, copper dissolving from the copper plate, while zinc is deposited on the zinc plate.
The cell, together with this balancing electromotive force, is thus a reversible system in true equilibrium, and the thermodynamical reasoning applicable to such systems can be used to examine its properties.
During a small electric transfer through the cell, the external work done is Ee, where E is the electromotive force.
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.