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INTRODUCTION.

LIFE is everywhere. "Nature lives," says Lewes ; every pore is bursting with life; every death is only a new birth; every grave a cradle." "The earth-dust of the universe," says Jean Paul, ❝is inspired by the breath of the great God. The world is brimming with life; every leaf on every tree is a land of spirits." The tendency 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.

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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° Fah., a range embracing almost every variety of conditions and circumstances.

The most cursory and superficial glance will recognise 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 grey stains, or parti-coloured 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 called spores or sporules, generally invisible to the naked eye, and differing from true seeds in germinating from any part of their surface instead of from two invariable points. Besides this grand distinguishing mark, they possess several other peculiar qualities in common. They consist of cells only, and hence are often called cellular plants, in contradistinction to those plants which are possessed of fibres and woody tissue. Their development is also superficial, growth taking place from the various terminal points; and hence they are called acrogens and thallogens, to distinguish them from monocotyledonous and dicotyledonous plants. Popularly, they are known as mosses, lichens, algæ, and fungi. They open up a vast field of physiological research. They constitute a microcosm, an imperium in imperio, a strange minute world underlying this great world of sense and sight, which, though unseen and unheeded by man, is yet ever in full and active operation around us. It is pleasant to turn aside for a while from the busy human world, with its ceaseless anxieties, sorrows and labours, to avert our gaze from the splendours

of forest and garden, from the visible display of green foliage and rainbow-coloured blossoms around us, and contemplate the silent and wonderful economy of that other world of minute or invisible vegetation with which we are so mysteriously related, though we know it not. There is something exceedingly interesting in tracing nature to her ultimate and simplest forms. The mind of man has a natural craving for the infinite. It delights to speculate either on the vast or the minute; and we are not surprised at the paradoxical remark of Linnæus, that nature appeared to him greatest in her least productions.

These plants once occupied the foremost position in the economy of nature. Like many decayed families whose founders were kings and mighty heroes, but whose descendants are beggars, they were once the aristocracy of the vegetable kingdom, though now reduced to the lowest ranks, and considered the canaille of vegetation. Geology reveals to us the extraordinary fact, that one whole volume of the earth's stony book is filled almost exclusively with their history. Life may have been ushered upon our globe through oceans of the lowest types of confervæ, long previous to the deposit of the oldest paleozoic rocks as known to us; and for myriads of ages these extremely simple and minute plants may have represented the only idea of life on earth. But passing from conjecture to the domain of established truth, we know of a certainty that at least throughout the vast periods of the carboniferous era, ferns, mosses, and still humbler plants, occupied the throne of the vegetable kingdom, and, by their countless numbers, their huge

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