In some species (Ascaris decipiens) the giant cell is replaced by an irregular mass of protoplasm containing a number of small nuclei.
Such a plasmodium bears, on its periphery, groups of rounded projections of protoplasm termed end-organs.
Opening closed by a plug of protoplasm (x, fig.
The cell is essentially an individualized mass of protoplasm containing a differentiated protoplasmic body, called a nucleus.
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.
The use of the term to mean the individualized nucleated mass of living protoplasm, which, whether with or without a limiting membrane, primitively forms the proximate histological element of the body of every organism, dates from the second quarter of the i9th century.
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.
The end wall is usually very thin, and the protoplasm on artificial contraction commonly sticks to it just as in a sieve-tube, though no perforation of the wall has been found.
When the sieve-tube has ceased to function and the protoplasm, slime strings, and callose have disappeared, the perforations through which the slime strings passed are left as relatively large holes, easily visible in some cases with low powers of the microscope, piercing the sieve.plate.
They possess a delicate Laticiferous layer of protoplasm, with numerous small nuclei lining Tissue the walls, while the interior of the tube (corresponding with the cell-vacuole) contains a fluid called latex, consisting of an emulsion of fine granules and drops of very various substances suspended in a watery medium in which various other substances (salts, sugars, rubber-producers, tannins, alkaloids and various enzymes) are dissolved.
These intermediate cells, like the ordinary parenchyma, frequently store starch, and the fibres themselves, though usually dead, sometimes retain their protoplasm, and in that case may also be used for starch accumulations.
They laid great stress on the nitrogenous nature of protoplasm, and noted that it preceded the formation of the cell-membrane.
The study of the differentiation of protoplasm was at that time seldom undertaken, and no particular attention was paid either to fixing it, to enable staining methods to be accurately applied to it, or to studying the action of chemical reagents upon it.
They have emphasized the statements of Von Mohl, Cohn, and other writers alluded to, that the protoplasm is here also the dominant factor of the body, and that all the peculiarities of the cell-wall can only be interpreted in the light of the needs of the living substance.
The study of simple organisms, many of which consist of nothing but a little mass of protoplasm, exhibiting a very rudimentary degree of differentiation, so far as our methods enable us to determine any at all, shows that the duties of existence can be discharged in the absence of any cell-wall.
We come, accordingly, to regard it as practically an exoskeleton, and its functions as distinctly subordinate to those of the protoplasm which it clothes.
With another similar protoplast, which constitutes what we call fertilization, the next stage in complexity already noted may be observed, the protoplasm becoming clothed by a cell-membrane.
What little differentiation can be found to exist in the protoplasm of the simple unicellular organism shows the importance of an adequate water-supply, and indeed, the dependence of life upon it.
The naked cells which have been alluded to live in water, and call therefore for no differentiation in connection with this necessity; but those which are surrounded by a cell-wall always develop within themselves a vacuole or cavity which occupies the greater part of their interior, and the hydrostatic pressure of whose contents keeps tha protoplasm in contact with the membrane, setting up a condition of turgidity.
The need for a constant supply of water is partly based upon the constitution of protoplasm, so far as we know it.
The protoplasm derives its food from substances in solution in the water; the various waste products which are incident to its life are excreted into it, and so removed from the sphere of its activity.
We have the formation of numerous mechanisms which have arisen in connection with the question of food supply, which may not only involve particular cells, but also lead to differentiation in the protoplasm of those cells, as in the development of the chloroplastids of the leaves and other green parts.
All physiology, consequently, must be based upon the identity of the protoplasm of all living beings.
Now, as the materials which plants absorb are carbon dioxide from the air, and various inorganic compounds from the soil, together with water, it is clear that if this view is correct, vegetable protoplasm must be fed in a very different way from animal, and on very different materials.
If we examine the seat of active growth in a young root or twig, we find that the cells in which the organic substance, the protoplasm, of the plant is being formed and increased, are not supplied with carbon dioxide and mineral matter, but with such elaborated material as sugar and proteid substances, or others closely allied to them.
We find them to consist of representatives of the great classes of foodstuffs on which animal protoplasm is nourished, and whose presence renders seeds such valuable material for animal consumptien.
The general vegetable protoplasm has not the capacity of being nourished by inorganic substances which are denied to the living substance of the animal world.
These bodies, known technically as chioroplaIts, are found embedded in the protoplasm of the cells of the mesophyll of foliage leaves, of certain of the cells of some of the leaves of the flower, and of the cortex of the young twigs and petioles.
The working of it is not at all completely understood at present, nor can we say exactly what is the part played by the pigment and what is the rfile of the protoplasm of the plastid.
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.
It is certain that their protoplasm cannot be nourished by inorganic compounds of nitrogen, any more than that of animals.
It may be, however, that there is no special mechanism, but that this power is a particular differentiation of a physiological kind, existing in all vegetable protoplasm, or in that of certain cells.
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.
As the tube grows down the hair it maintains its own independence, and does not fuse with the contents of the root-hair, whose protoplasm remains quite distinct and separate.
The cells in which the fungoid organism is vigorously flourishing are exceedingly active, showing large size, brilliant nuclei, protoplasm and vacuole, all of which give signs of iptense metabolic activity.
In many cases the digestion of reserve food materials is effected by the direct action of the protoplasm, without the intervention of enzymes.
There is no direct connection between the two, the oxygen is absorbed almost immediately by the protoplasm, and appears to enter into some kind of chemical union with it.
The protoplasm is in a condition of instability and is continually breaking down to a certain extent, giving rise to various substances of different degrees of complexity, some of which are again built up by it into its own substances, and others, more simple in composition, are given off.
These respiratory processes are associated with the liberation of energy by the protoplasm, energy which it applies to various purposes.
The assimilation of complex foods consequently may be regarded as supplying the protoplasm with a potential store of energy, as well as building tip its substance.
Indeed, the construction of protoplasm itself indicates the same thing.
It has been suggested by several botanists, with considerable plausibility, that the ultra-violet or chemical rays can be absorbed and utilized by the protoplasm without the intervention of any pigment such as chlorophyll.