Page:Popular Science Monthly Volume 3.djvu/484

470 to vegetate is a ceaseless power. It has been in operation from the earliest ages of the earth, ever since living beings were capable of existing upon its surface; and so active in the past history of the globe has been this tendency, that most of the superficial rocks of the earth's crust are composed of the remains of plants. It operates with undiminished and tireless energy still. Vegetation takes place upon almost every substance; upon the bark of trees, upon naked rocks, upon the roofs of houses, upon dead and living animal substances, upon glass when not constantly kept clean, and even on iron which had been subjected to a red heat a short time before. Zoologists tell us, when speaking of animalcules, that not a drop of stagnant water, not a speck of vegetable or animal tissue, not a portion of organic matter, but has its own appropriate inhabitants. The same may be said of plants; for we can hardly point to a single portion of the earth's surface which is not tenanted by some vegetable form whose structure is wonderfully adapted to its situation and requirements. Even in the hottest thermal springs, and on the eternal snows of the arctic regions, peculiar forms of vegetation have been found. From the deepest recesses of the earth to which the air can penetrate, to the summits of the loftiest mountains; from the almost unfathomable depths of the ocean to the highest clouds; from pole to pole, the vast stratum of vegetable life extends; while it ranges from a temperature of 35° to 135° Fahr., a range embracing almost every variety of conditions and circumstances.

The most cursory and superficial glance will recognize in every scene a class of plants whose singular appearances, habits, and modes of growth, so prominently distinguish them from the trees and flowers around, that they might seem hardly entitled to a place in the vegetable kingdom at all. On walls by the wayside, on rocks on the hills, and on trees in the woods, we see tiny green tufts and gray stains, or party-colored rosettes spreading themselves, easily dried by the heat of the sun, and easily revived by the rain. In almost every stream, lake, ditch, or any collection of standing or moving water, we observe a green, slimy matter, forming a scum on the surface, or floating in long filaments in the depths. On almost every fallen leaf and decayed branch, fleshy, gelatinous bodies of different forms and sizes meet our eye. Sometimes all these different objects appear growing on the same substance. If we examine a fallen, partially-decayed twig, half-buried in the earth in a wood, we may find it completely covered with various representatives of these different vegetable growths; and nothing surely can give us a more striking or convincing proof of the universal diffusion of life. All these different plants belong to the second great division of the vegetable kingdom, to which the name of Cryptogamia has been given, on account of the absence, in all the members, of those prominent organs which are essential to the production of perfect seed. They are propagated by little embryo plants