Associated with the conducting parenchyma are frequently found hydroids identical in character with those of the central strand of the stem, and no doubt serving to conduct water to or from the leaf according as the latter is acting as a transpiring or a waterabsorbing organ.
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.
As such its consideration falls outside the scheme of this article, but in one small and peculiar group of these plants, the Anthoceroteae, a distinct assimilating and transpiring system is found in the wall of the very long cylindrical capsule, clearly rendering the sporo-.
M and thin, flat, assimilating, and transpiring appendages osses.
The midrib bears above a series of closely set, vertical, longitudinally-running plates of green assimilative cells over which the wings close in dry air so as to protect the assimilative and transpiring plates from excessive evaporation of water.
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.
The water stored in such a time supplies the immediate need of the transpiring cells and prevents the injury which would result from their excessive depletion.
The transpiring surface of xerophytes is frequently reduced.
This is the main transpiring tissue, and is protected from direct illumination and consequent too great evaporation.