Plants not producing true flowers, but reproducing themselves by means of spores instead of seeds, the spores consisting merely of simple cells, and not containing an embryo.
This series is subdivided into three classes:
1. Pteridophytes, embracing Ferns, Horsetails, and Club-Mosses. 2. Bryophytes, embracing the true Mosses and Liverworts. 3. Thallophytes, embracing Algae and Fungi.
Types of all of these have already been described and illustrated in Part I. We shall here enumerate the common representatives of the Pteridophytes only.
These beautiful plants are favourites everywhere, and we shall therefore enter into a description of their characteristics with sufficient minuteness to enable the young student to determine with tolerable certainty the names of such representatives of the Family as he is likely to meet with commonly.
In Chapter XXI. of Part I. will be found a full account of the common Polypody, with which it is assumed the student is already familiar.
Fig. 262 shows a portion of the frond of the Common Brake (Pteris aquilina). Here the frond is several times compound. The first or largest divisions to the right and left are called pinnoe.
The secondary divisions (or first divisions of the pinnae) are the pinnules. The stem, as in the Polypody, and in fact in all our Ferns which have a stem at all, is a rootstock or rhizome. But here we miss the fruit-dots or sori, so conspicuous in our first example. In this case it will be found that there is a continuous line of sporangia around the margin of every one of the pinnules of the frond, and that the edge of the pinnule is reflexed so as to cover the line of spore-cases. Fig. 263 is a very much magnified view of one of the lobes of a pinnule, with the edge rolled back to show the sporangia. Some of the sporangia are removed to show a line which runs across the ends of the forking veins. To this the sporangia are attached. The veins, it will be seen, do not form a net-work, and so are free, as in Polypody. Observe, then, that in Polypody the sori are not covered, whilst in Pteris the opposite is the case. The covering of the fruit-dots is technically known as the indusium. The individual spore-cases are alike in both plants Fig. 264 shows a frond of one of our commonest Shield-Ferns (Aspidium acrostichoides). It is simply pinnate. The stipe is thickly beset with rusty-looking", chaff-like scales. The veins are free, as before. The sori or fruit-dots are on the back of the upper pinnae, but they are neither collected in naked clusters, as in Polypody, nor are they covered by the edge of the frond as in the Brake. Here each cluster has an indusium of its own. The indusium is round, and attached to the frond by its depressed centre (peltate). Fig. 265 shows an enlarged portion of a pinna, with the sporangia escaping from beneath the indusium. From one forking. vein the sporangia are stripped off to show where they have been attached. The separate sporangia discharge their spores in the manner represented in the account of Polypody. In some Ferns the fruit-dots are elongated instead of being round, and the indusium is attached to the frond by one edge only, being free on the other. Sometimes two long fruit-dots will be found side by side, the free edges of the indusia being towards each other, so that there is the appearance of one long fruit-dot with an indusium split down the centre.
Fig. 266 represents a frond of a very common swamp Fern, Onoclea Sensibilis, or Sensitive Fern. It is deeply pinnatifid, and on one of the lobes the veining is represented. Here the veins are not free, but as they form a net-work they are said to be reticulated. You will look in vain on this frond for fruit-dots, but beside it grows another, very different in appearance, - so different that you will hardly believe it to be a frond at all. It is shown in Fig. 267. It is twice pinnate, the pinnules being little globular bodies, one of which, much magnified, is shown in Fig. 268. You may open out one of these little globes, and then you will have something like what is shown in an enlarged form in Fig. 269. It now looks more like a pinnule than when it was rolled up, and it now also displays the fruit-dots on the veins inside. Here, then, we have evidently two kinds of frond. That bearing the fruit-dots we shall call the fertile frond, and the other we shall call the sterile one. You must not look upon the pinnule in which the sori are wrapped up as an indusium.
Sori which are wrapped up in this way have an indusium of their own besides, but in this plant it is so obscure as to be very difficult to observe.
The spore-cases burst open by means of an elastic ring as before.
Fig. 270 represents one of the Moon-worts (Botrychi-um Virginicum), very common in our rich woods everywhere. Here we have a single frond, but made up manifestly of two distinct portions, the lower sterile and the upper fertile. Both portions are thrice-pinnate. The ultimate divisions of the fertile segment are little globular bodies, but you cannot unroll them as in the case of the Onoclea. Fig. 271 shows a couple of them greatly enlarged. There is a slit across the middle of each, and one of the slits is partially open, disclosing the spores inside. Each little globe is, in fact, a spore-case or sporangium, so that here we have something quite different from what we have so far met with. Up to this point we have found the sporangia collected into dots or lines or clusters of some sort. In the Moonwort the sporangia are separate and naked, and instead of bursting through the action of an elastic ring, they open by a horizontal slit and discharge their spores. In other Ferns, as the Osmunda, the sporangia are somewhat similar, but burst open by a vertical instead of a horizontal slit.
Observe that the frond of Botrychium is not circinate in the bud.
We shall now proceed to describe the commonly occurring representatives of the Fern Family.