Fig. 64. A moss plant. Fig. 65. A mushroom, a common type of the fungi, which include also puffballs, molds, and many disease-causing microscopic organisms. Fig. 66. A common seaweed, a representative of the algæ, which include the green scum on the top of ponds, and the kelp from which fertilizer is now being made. Fig. 67. A lichen, a common cryptogamous plant on logs and rocks. Our native kinds are usually grayish-green in color.
known trees. And yet other inhabitants of the water, certain kinds that float freely, are microscopic in size. The latter occur in such enormous numbers that their tiny decomposed skeletons after dropping to the bottom of the sea form the diatomaceous earth, so much used in polishing machinery. The commercial product now comes from deposits of these skeletons laid down in past ages, which, due to changes in the land and water surfaces of the earth, are now found in Virginia, Nevada, California, and in Bohemia. All these must have been in the bed of waters long since gone, which teemed with these microscopic organisms. To-day there are over ten thousand different kinds known, yet so small are they that their dimensions are measured in thousandths of an inch!
Somewhat lower in the scale of life—and by this we mean simpler in structure—than the ferns are the mosses. ([Figure 64].) There are thousands of different kinds, but everyone is familiar with the collective growth of the commoner sorts which makes the velvety mossy carpet in our woods. The individual plants are small, but in many kinds sufficiently large to be seen without a microscope. Most important of all, practically every one of them has the ordinary green color of the better known plants, and as we shall see in the section devoted to “Leaves as Factories for the Making of Food,” that stamps them at once as plants, if other things did not.
Mosses are almost infinite in their habits, some growing on the dry rocks or trunks of trees, many growing in moist woods, some in the water, and immense quantities of certain kinds in bogs. The peculiar bog mosses, known as sphagnum, play an important part in forming peat and perhaps coal. While mosses are otherwise not of much commercial importance, they are among nature’s most beautiful ground covers, carpeting many a nook and dell with a soft, velvety, almost cushionlike growth.
Although they are rather small, they appear to have a somewhat definite stem and tiny leaflike appendages of it, without, however, having the vascular system found in all ferns. Mosses might almost be considered miniature ferns, of which they are perhaps only simple ancestors. Their vegetative or green parts vary much in shape, size, and the arrangement of the tiny leaflike appendages, and while most of them are a beautiful bright green, nearly all the bog or sphagnum mosses are rather ashy gray in color. In most of the typical mosses there arises from among the vegetative growth of them a slender stalk, at the top of which is a small capsulelike organ. This contains the spores, and it is upon this long slender stalk and its spore-filled capsule, really marvelous in its internal structure and mechanism for the discharge of the spores, that mosses depend for their reproduction. As in the case of the ferns this process will be considered later, along with that of some other plants. This whole story of how plants produce their young, perhaps the most fascinating of any part of the study of plant life, is so fundamentally a part of their history and shows nature in her most maternal moods, that a special chapter will be devoted to it. There we shall see, as a whole, how these vastly different acts of fertilization and reproduction are, in different groups of plants, all responses to that insistent command for life, more life, in a never-ending stream.