There is a point whence life and vegetation seem to diverge--the simple cell; where the algæ meet the monads, and most mysterious processes and elaborations are carried on by means the simplest but most astounding. Of cell upon cell are the sea-weeds built, and by cells or spores cast loose from their substance are their species reproduced, as certainly and as surely as plants by the marriage of the flowers. Of cellular tissue entirely does the sea-weed consist; of cell upon cell alone is woven all the varied drapery of the deep. A mere sac, empty, or containing a fluid or granular substance, absorbs the surrounding fluids, assimilates them in its membranous walls, consolidates their carbon and nutritious substances, grows, divides, each portion swells again to its parent size, each again divides, and so the splitting cells increase and multiply. The rapidity with which some of the common confervæ of our ponds are thus developed is well known; and it is not unusual to find loathsome pools, that were black at dawn with decomposing filth, covered at eve with a floating verdure rapidly and energetically extracting its nutriment out of the pollution, and liberating the gas of animal life--oxygen--into the atmosphere, in lieu of pestilential effluvia. The snow-plant, the _Protococcus nivalis_, is perhaps the best-known instance of the rapid development of cell-plants properly so called. In a few hours whole tracts of the white snow of northern lands will assume the hue of the battle-field; and from another species the waters of the Arabian Gulf have acquired their memorable name of Red Sea.
Above the limits of the lichen incrusting the peaks of mountains, and in the unplumbed abysses of the deep below the region of the nullipore, there the cell-plants swarm by myriads; and even the air powders the ropes of ships at sea with the atomic dust that had vegetated among the clouds.
I have claimed for the sea-weeds the attractions of simplicity, and I claim beauty of outlines and gracefulness of forms even for the simplest of the simple--the cell-plants. Forms! outlines of cell-plants! Would not a single species content the naturalist? The ever-varying Hand that is traced in all around has touched these lowly objects with charms and wonders in the most exquisite modifications of form and the most delicate sculpture. The invisible is not the less beautiful that it is unseen; the physician owes much to these little things--why not the artist? Are there no laws of symmetry in natural objects, as there are of mechanics and of force? no sympathetic principles of harmony of colour with form, as of structure with locomotion or fixity? Even in these humble plants there are traces of that divine delicacy which may be observed and appreciated--an expression of that one word which cannot be spoken.