Fig. 156.—A Moss. A,
a plant with spore-case
still covered by hood (c)
(× 1). B, a plant with ripe
spore-case (k); s, stalk;
d, lid; rh, hairs (× 1). C,
mature spore-case with
lid (d) removed; p, fringe
of teeth (× 3).
The liverwort also gives rise to a spore-bearing generation, but in this case it consists merely of a small, round, spore-box, dark-green in colour, which is carried on the summit of a white stalk—the whole looking somewhat like a stout pin. In February, or early March, the spore-boxes may be seen upon the upper surface of the plant as small balls, perhaps one-sixteenth of an inch in diameter, protruding from the mouth of a little pocket in which their early stages are passed. About May, their stalks lengthen so rapidly that in a few days the spore-boxes are lifted to a height of two or three inches. Then each box opens by its wall splitting into four, and the spores are liberated to germinate and form new liverworts. Having thus shed the spores, the box and stalk die down.
The complete life-cycle of a liverwort thus includes two unlike generations, as that of a fern does; but it is a different generation which attains the greater development in the two cases. The ordinary fern is the spore-bearing generation; the “ordinary” liverwort is the sexual generation, and its sporing offspring is not a separate plant at all, but a mere stalked box, almost entirely dependent upon its parent.
The mosses.—A moss-plant appears at first sight to be very similar in its general features to one of the higher plants; for it has a little stem, bearing flattened green leaves which build up carbonaceous food in the usual way. It has no true roots, but fine hairs penetrate the soil and do the work of roots by taking up solutions of mineral food. It is all the more remarkable, therefore, to find from its method of reproduction that the moss-plant belongs to the generation which corresponds to the prothallus stage of a fern’s life-history, and not to the leafy, sporing generation which it somewhat resembles superficially.
The sexual organs of a moss are essentially of the same type as those which a prothallus bears, and here also the tiny male cells gain access to the female cells by swimming through a drop of rain or dew. The result of fertilisation is an embryo which, however, grows up to form, not a plant with stem and leaves, but a stalked spore-case only.
In a tuft of the moss Funaria, which is so common in all country places, several stages of development of the spore-cases may usually be seen. [Fig. 156] represents a moss which is very similar to Funaria but larger. In A, the spore-case is still covered by a conical hood (c). In B, the stalk (s) has grown much longer, and the hood has dropped off. The spore-case or capsule (k) is now seen to be a pear-shaped body, closed by the lid (d). When the spores are ripe, the lid becomes detached. The mouth of the nodding capsule is still blocked, however, by a number of teeth ([Fig. 156], C, p) which remain close together in damp weather. In dry weather the teeth separate, and allow the spores to fall out. When a moss spore falls in a favourable situation it germinates to form a fine, branching network of green threads, from which new moss-plants arise as buds.
The obvious plant of a moss—like that of a liverwort—therefore corresponds to the prothallus generation of a fern or horsetail. Its sporing generation, corresponding to the obvious fern-plant or horsetail, is a stalked spore-case, which is always more or less dependent on its parent and dies down as soon as its work of scattering the spores is accomplished.
41. THE COMMON MUSHROOM.
1. Habit of growth.—In what situations do you find mushrooms growing? In what kinds of weather and at what time of the year are they most abundant? Take up a mushroom with a trowel, and carefully wash the earth from the lower part to see the tangle of white threads (called the mycelium), which is the underground part of the plant. See that several of these run into the bottom of the stalk. On the underground mycelium look for young mushrooms in the “button” stage. Look around, and try to get a series of mushrooms showing all stages from the smallest buttons to fully-opened specimens.
2. Structure.—Draw a side view (natural size) of a full-grown mushroom, showing the stalk and cap. Running round the stalk notice a ragged flap, called the collar. What is the height of the collar from the base of the stalk? Examine younger mushrooms to find what the collar really is. Notice that in young specimens a membrane or veil stretches from the edge of the cap to the stalk, and that as the mushroom grows larger this veil is torn away from the cap ([Fig. 157]), and remains as a ragged flap (the collar) on the stalk. In young specimens, therefore, the lower side of the cap is completely shut in by the veil, while in fully-grown ones it is exposed.