The whole arrangement has a strong resemblance to the lacunae, mesophyll and stomata, which form the assimilative and transpiring (water-evaporating) apparatus in the leaves of flowering plants.
A richly chlorophyllous tissue, with numerous intercellular spaces communicates with the exterior by stomata, strikingly similar to those of the vascular plants (see below).
Frequently, also, a considerable differentiation of vegetative tissue occurs in the wall of the spore-capsule itself, and in some of the higher forms a special assimilating and transpiring organ situated just below the capsule at the top of the seta, with a richly lacunar chlorophyllous parenchyma and stomata like those of the wall of the capsule in the Anthocerotean liverworts.
At intervals it is interrupted by pores (stomata) leading from the air outside to the system of intercellular spaces below.
Each stoma is surrounded by a pair of peculiarly modified Stomata epidermal cells called guard-cells (fig.
The structure of the stomata of the sporophyte of vascular plants is fundamentally the same as that of the stomata on the sporogonium of the true mosses and of the liverwort A nihoceros.
Stomata are often situated at the bottom of pits in the surface of the leaf.
The stomata serve for all gaseous interchange between the plant and the surrounding air.
A very common function of hairs is to diminish transpiration, by creating a still atmosphere between them, as in the case of the sunk stomata already mentioned.
The pores of the water-stomata are the outlets of the hydathode.
A land plant has nearly always to protect itself against over-transpiration, and for this reason the stomata of the typical dorsiventral leaf (fig.
The stomata are in direct communication with the ample system of intercellular spaces which is found in the loosely arranged mesophyll (spongy tissue) on that side.
Leaves whose blades are normally held in a vertical position possess palisade tissue and stomata on both sides (isobilateral leaves) (fig.
It alse always possesses a well-developed lacunar system communicating with the external air through stomata (in the young stem) or lenticel~ (see below).
The lenticels of the stem are usually formed beneath stomata, whose function they take up after the stomata have been ruptured and cast off with the rest of the epidermis.
This system of channels is in communication with the outer atmosphere through numerous small apertures, known as stomata, which are abundant upon the leaves and young twigs, and gaseous interchange between the plant and the air is by their assistance rendered constant and safe.
They are without stomata on their submerged portions, and the entry of gases can only take place by diffusion from the water through their external cells, which are not cuticularized.
Those which are only partially submerged bear stomata on their exposed portions, so that their environment approximates towards that of a terrestrial plant, but the communication even in their case is much less easy and complete, so that they need amuchlarger reservoir of air in their interior.
The latter ultimately reaches the external air by diffusion through the stomata, whose dimensions vary in proportion as the amount of water in the epidermal cells becomes greater or less.
The entry of gases into, and exit from, the cells, as well as the actual exhalation of watery vapour from the latter, take place in the intercellular space system of which the stomata are the outlets.
The opening and closing of the stomata is the result of variation in the turgidity 01 their guard cells, which is immediately affected by the condition of turgidity of the cells of the epidermis contiguous to them.
This opening and closing of the stomata must be looked upon as having a direct bearing only on the emission of watery ~vapour.
The spot or patch is an area of injury; on (or in) it the cell-contents are suffering destruction from shading, blocking of stomata, loss of substance or direct mechanical injury, and the plant suffers in proportion to the area of leaf surface put out of action.
Sclerophyllous leaves are ually characterized by entire or sub-entire margins, a thick cuticle, riall but rarely sunken stomata, a we1l-developed and close-set ilisade tissue and a feeble system of air-spaces.
Stomata are often absent, absorption and excretion of gases in solution being carried on through the epidermal layer.
Switch plants, such as Retama Retam and broom (Cytisus scoparius), have reduced leaves and some assimilating tissue in their stems; and stomata occur in grooves on the stem.
Many xerophytes are hairy or have sunken stomata which may be further protected by partial plugs of wax:
The stomata are frequently in grooves: the leaves are frequently rolledsometimes permanently so, whilst sometimes the leaves roll up only during unfavourable weather.
These adaptations tend to lessen the amount of transpiration by protecting the stomata from the movements of the air.
Warming states that the stomata of true, succulent, littoral halophytic herbs, in cases so far investigated, are not sunken (1909: 221).
It is possible, however, that the absence of sunken stomata, and the occurrence of some other halophytic features, are related merely to the succulent habit and not to halophytism, for succulent species often occur on non-saline soils.
Their stomata are frequently not limited to the underside of the leaves, but may occur scattered all over the epidermal surface.
Stomata occur on both surfaces of the leaves, and, with the peculiar hair structure render the microscopic appearance of the plant highly characteristic.
The habitats which they affect are the hot, dry regions of tropical America, the aridity of which they are enabled to withstand in consequence of the thickness of their skin and the paucity of evaporating pores or stomata with which they are furnished, - these conditions not permitting the moisture they contain to be carried off too rapidly; the thick fleshy stems and branches contain a store of water.
Transpiration is loss of water by the plant by evaporation, chiefly from the minute pores or stomata on the leaves.
Cacti, euphorbias, &c.) from hot, dry and almost waterless regions where evaporation would be excessive, the leaf surface, and consequently the number of stomata, are reduced to a minimum, as it would be fatal to such plants to exhale vapour as freely in those regions as the broad-leaved plants that grow in places where there is abundance of moisture.
The other genera are more purely parasitic; the mycelium usually sends haustoria into the cells of the host and puts out branched, aerial conidiophores through the stomata, the branches of which abstrict numerous "conidia"; these either germinate directly or their contents break up into zoospores (fig.
Tophthora infestans passing K, Germination of the zoospores through the stomata D, on formed in the sporangia.
If the membrane is of some impermeable substance, like gold leaf, the hyphae cannot dissolve its way through, but the tip finds the most minute pore and traverses the barrier by means of it, as it does a stoma on a leaf, We may hence conclude that a parasitic hyphae pierces some plants or their stomata and refuses to enter others, because in the former case there are chemotropically attractive substances present which are absent from the latter, or are there replaced by repellent poisonous or protective substances such as enzymes or antitoxins.
The epidermis is continuous except where stomata or spaces bounded by specialized cells communicate with intercellular spaces in the interior of the leaf.
2, ei) that stomata, st, are produced, and it is there also that hairs, p, usually occur.
The upper epidermis alone possesses only small intercellular spaces, except where stomata happen to be present (fig.
2, p), leaving air-spaces between them, which communicate with stomata; on this account the tissue has received the name of spongy.
The flat surface is spread to allow the maximum amount of sunlight to fall upon it, as it is by the absorption of energy from the sun's rays by means of the chlorophyll contained in the cells of the leaf that the building up of plant food is rendered possible; this process is known as photo-synthesis; the first stage is the combination of carbon dioxide, absorbed from the air taken in through the stomata into the living cells of the leaf, with water which is brought into the leaf by the wood-vessels.
A large proportion of the water which ascends to the leaf acts merely as a carrier for the other raw food materials and is got rid of from the leaf in the form of water vapour through the stomata - this process is known as transpiration.
The lower surface of the potato leaf is furnished with numerous organs of transpiration or stomata, which are narrow orifices opening into the leaf and from which moisture is transpired in the form of vapour.
' ing longitudinal ridges, generally on the upper face; the stomata are in lines in the intervening furrows.
The rolling up acts as a protection from too great loss of water, the exposed surface being specially protected to this end by a strong cuticle, the majority or all of the stomata occurring on the protected surface.
The characters of leaves most useful for diagnostic purposes are the position of the stomata, the presence and arrangement of resin-canals, the structure of the mesophyll and vascular bundles.
The stomata are frequently arranged in rows, their position being marked by two white bands of wax on the leaf-surface.