The sexual organs are rarely met with, but should be looked for late in autumn or early spring. The antheridial branches are often bright-colored, red or yellow, so as to be very conspicuous. The capsules, which are not often found, are larger than in most of the common mosses, and quite destitute of a stalk, the apparent stalk being a prolongation of the axis of the plant in the top of which the base of the sporogonium is imbedded. The capsule is nearly globular, opening by a lid at the top ([Fig. 64], B).
A microscopical examination of the leaves, which are quite destitute of a midrib, shows them to be composed of a network of narrow chlorophyll-bearing cells surrounding much larger empty ones whose walls are marked with transverse thickenings, and perforated here and there with large, round holes ([Fig. 64], C). It is to the presence of these empty cells that the plant owes its peculiar spongy texture, the growing plants being fairly saturated with water.
The Andreæaceæ are very small, and not at all common. The capsule splits into four valves, something like a liverwort.
The Phascaceæ are small mosses growing on the ground or low down on the trunks of trees, etc. They differ principally from the common mosses in having the capsule open irregularly and not by a lid. The commonest forms belong to the genus Phascum ([Fig. 65], A).
The vast majority of the mosses the student is likely to meet with belong to the last order, and agree in the main with the one described. Some of the commoner forms are shown in [Figure 65].
CHAPTER XII.
SUB-KINGDOM V.
Pteridophytes.
If we compare the structure of the sporogonium of a moss or liverwort with the plant bearing the sexual organs, we find that its tissues are better differentiated, and that it is on the whole a more complex structure than the plant that bears it. It, however, remains attached to the parent plant, deriving its nourishment in part through the “foot” by means of which it is attached to the plant.
In the Pteridophytes, however, we find that the sporogonium becomes very much more developed, and finally becomes entirely detached from the sexual plant, developing in most cases roots that fasten it to the ground, after which it may live for many years, and reach a very large size.
The sexual plant, which is here called the “prothallium,” is of very simple structure, resembling the lower liverworts usually, and never reaches more than about a centimetre in diameter, and is often much smaller than this.