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Updated: May 13, 2025
It has long been known that the leaves of these plants, and of several allied species, are attacked by a fungus, the mycelium of which spreads in the leaf passages, and gives rise to powdery masses of orange yellow spores, arranged in vertical rows beneath the stomata: these powdery masses of spores burst forth through the epidermis, but are not clothed by any covering, such as the Æcidia of Peridermium Pini, for instance.
Goodale says: "Whether it is best to try to explain to the pupils the structure of these valves, or stomata, must be left to each teacher. It would seem advisable to pass by the subject untouched, unless the teacher has become reasonably familiar with it by practical microscopical study of leaves.
So that while we have undeniable proof that the contrasted influences of the medium on the two sides, initiate the differentiation, we have also proof that the completion of it is determined by the transmitted structure of the type; since it is impossible to ascribe the development of stomata to the direct action of air and light.
This term is used to denote the evaporation of water from a plant. The evaporation takes place principally through breathing pores, which are scattered all over the surface of leaves and young stems. The breathing pores, or stomata, of the leaves, are small openings in the epidermis through which the air can pass into the interior of the plant. Each of these openings is called a stoma.
In such emergencies these little stomata, or mouths, shut up partly or completely, and so do much to check the exhalation. When moisture is given to the roots, these mouths open again, and if our eyes were fine enough we should see the vapor passing out." "I never appreciated the fact before that plants are so thoroughly alive."
The commonest forms are Erigeron Asteroides, Vernonia cinerea, Laurea pinnatifida, Vicoa auriculata, Heylandia latebrosa and Chrysopogon montanus. In direct contrast with the ordinary desert-types they have a thin epidermis, with exposed stomata, features that ordinarily were characteristic of species of moister regions.
If a diseased potato leaf be examined with the naked eye, it will be seen that, on the upper surface, there is an irregular brownish black spot, and if the under surface of the leaf be looked at carefully, the brown spot is also visible, but it will be seen to be covered with a very faint white bloom, due to the growth of the fungus from the microscopic openings or "stomata," which exist in large numbers on the under surface of most green leaves.
"As only one areola belongs to each cell, and as in many cases where it exists in the common cells of the epidermis, it is also visible in the cutaneous glands or stomata, and in these is always double one being on each side of the limb it is highly probable that the cutaneous gland is in all cases composed of two cells of peculiar form, the line of union being the longitudinal axis of the disk or pore.
It is known that with fallen leaves the starch-grains are preserved in the guard-cells of the stomata. Now in several cases the starch had partially or wholly disappeared from these cells, in the parts which had been moistened by the secretion; while it was still well preserved in the other parts of the same leaves. Sometimes the starch was dissolved out of only one of the two guard-cells.
There is one leaf on which there are over one hundred and fifty thousand. They are called stomata, or breathing-pores, and are on both sides of the leaf in most plants, but usually are in far greater abundance on the lower side. The plant draws its food from the air and soil from the latter in liquid form and this substance must be concentrated and assimilated.
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