CHAPTER XXVII.

ALGÆ AND FUNGI

=The last big family of plants is that containing the simplest plants of all.= They are often very small and apparently unimportant, sometimes so small that we cannot study them at all without magnifying them very much with the microscope. In other cases they are quite large and easy to see; for example, the big red and brown seaweeds, and the many toadstools in the autumn woods. Sometimes they may even be very huge indeed, as are some of the seaweeds which grow in tropical seas. All the same, though we examine one which is as big as can be, it is really more simple in its detail than the mosses.

In very ~many of the algæ and fungi, the whole plant body consists only of one single cell~. When this is the case, the plant lives floating or swimming about in water, or in very damp places. In rain-water which has stood for a long time you may find numbers of these tiny algæ. If you put some of the water in a glass tube and hold it against the light you may just see them, with a magnifying-glass, as specks of green, often swimming actively about.

The fine green “scum” which floats on many ponds and slow-moving streams consists of masses of these simple plants, in this case generally of forms in which the single cells keep attached together in long rows or chains, forming hair-like plants. Colourless plants of this kind are the fungi, which are often built on the same plan as the hair-like green algæ, only they do no food-building work for themselves, but live as parasites on other things. This is the case in many moulds and the plants which form potato-disease, and, in fact, the greatest number of plant-diseases are caused by such simple parasites.

All these plants are very small and simple, and as you can see at once, are not at all to be compared even with the mosses, but there are others which seem to be more complicated, as are the big seaweeds and the toadstools. Let us see how it is they are put in the same family as the simplest plants of all.

You can see, even with your magnifying-glass, that they have no special “water-pipes” in what you may call their “stem,” (for want of a better name), but that their whole body is built up of numbers of soft cells all very much alike, which twine in and out, and build a kind of soft weft; they have no really marked out stem and leaves. Look at a toadstool, for example, there is just a stalk and a cap spreading out above ground, while under the ground there are many twining thread-like strands (~see~ fig. 133).

Even in the seaweeds, which may seem to have stems, you will find that such is not really the case. They have generally a flat body, which is thin at the edges, with a stronger mid-rib, and the flat edges get worn away in the older parts of the plant, and so leave the mid-rib looking like a stem, though it is not so really (~see~ fig. 134).

When we come to look for flowers or even spore capsules, we see still more clearly how simple these plants are; they have not nearly such a complicated history as the moss. For example, in the toadstools we find that there are many spores formed directly on its lower surface, on the “gills,” and these grow out to form new toadstool plants. You can see the spores if you cut off a toadstool or mushroom head which looks full grown and is quite expanded, and then lay it on a sheet of gummed paper over-night, with the gills downwards, and another beside it with the gills up. Next day you will find that the paper under the one where the gills were downwards is covered with radiating lines of spores, just as they fell from the gills, and repeating their pattern.

The seaweeds have the most complicated way of forming spores of any of this family. There are special little swellings at the ends of the plant, as in the ordinary bladder-wrack, for example (fig. 135 (~s~)), and in these are formed the cells which will give rise to new plants. The other simple bladders (fig. 135 (~f~)) are only full of air, and act as floats to keep the plant up in the water.

In this the simplest family of all, we find more variety in the appearance of its members than in any of the others, so that it may seem to be rather difficult to recognise the plants which belong to it. Perhaps the easiest way of settling this, is to see if the plant fits into any of the other families, and if it never has flowers nor cones, neither fern spore-capsules nor the big spore-capsules of the moss family, then you are fairly safe in classing it with the simplest plants.

Very many of the plants of this family are found living in water, which is perhaps one of the reasons that they can afford to be so simple, because the water protects them from many of the dangers land-plants have to prepare against, such as wind, drought, or too much sunshine. This is the simplest family of real, undoubted plants; but there is one class still simpler, and that is the family of ~bacteria~, about which you must have heard much, as many of them cause our diseases, though others do much valuable work for us. All the same, we will leave these little creatures alone, and content ourselves with the five great families of plants which we can see with our own eyes.