reality depends for existence. Moreover the whole of the mould in which the higher orders of plants grow, is formed by the decomposition of the more humble grades, especially the lichens, which first take possession of the surface of bare rocks and stones, and furnish by their death food fit for the sustenance of those which follow them. Like the higher orders of vegetation, these minute plants excrete oxygen, and thus in the ocean may supply this vital element for the respiration of the various corresponding minute animal organisms which inhabit the depths of the sea and which cannot come to the surface to get it, so that the two thus supporting each other, form food for all the higher marine animals, which are finally eaten by man. So that upon some of these minute and apparently useless creatures hang the lives and well-being of many of the most important vegetables and animals. Dr. Lindley divides the acrogens into the following orders:-- 1. ALGÆ (Algals), including Sea-weeds, &c. The Algæ include the lowest of all the vegetative organisms, the "Protophytes" (first plants). These have no individual parts, but consist of living cells, propagating by sub-division or by the union of two cells into one, causing the formation of "nuclei" or smaller cells within them, each of which becomes a parent cell after the rupture of the cell-membrane which contained them. Dr. Carpenter, in his "History of the Microscope," says:--"The life-history of one of these uni-cellular plants in its most simple form, can scarcely be better exemplified than in the _Palmogloea macrococca_, one of those humble forms of vegetation which spreads itself as a green slime over damp stones, walls, &c. When this slime is examined with the microscope, it is found to consist of a multitude of green cells, each surrounded by a gelatinous envelope; the cell, which does not seem to have any distinct membranous wall, is filled with granular particles of a green colour, and a 'nucleus' may sometimes be distinguished through the midst of these. When treated with tincture of iodine, however, the green contents of the cell are turned to a brownish hue, and a dark-brown nucleus is distinctly shown. Other cells are seen, which are considerably elongated, some of them beginning to present a sort of hour-glass contraction across the middle; in these is commencing that curious _multiplication by duplicative subdivision_ which is the mode in which increase nearly always takes place throughout the vegetable kingdom." [Illustration: Fucus Vesiculosus.]