This power of individual increase, or reproduction, is the very summit of vital manifestation; indeed Coleridge, in his Theory of Life, (in which he says, "I define life as the _principle of individuation_, or the power which unites a given _all_ into a whole that is presupposed by all its parts,") places reproduction in the first rank, and expresses his hypothesis thus: "the constituent forces of life in the human living body are, first, the power of length or reproduction; 2nd, the power of surface, or irritability; 3rd, the power of depth, or sensibility--life itself is neither of these separately, but the copula of all three." Extensive research is not required to shew that many thinking men believe in the existence of living organic beings, as the elements of contagious and epidemic diseases; the idea indeed seems to flow spontaneously in that direction. Whenever thought, and enduring contemplation, have been concentrated on the subject, the result appears to have been the same, a firm conviction in each individual mind that a vital force must be in operation; or as Schlegel would define it, "a living reproductive power, capable of and designed to develope and propagate itself."--"Its Maker originally fixed and assigned to it the end towards which all its efforts were ultimately to be directed." Referring further to beings having the property of reproduction and propagation, he says, (using {15} the word nature here evidently as the vital principle for want of a better term,) "Nature indeed is not free like man, but still is not a piece of dead clockwork. _There is life in it._"--"Thus we know that even plants sleep, and that they too as much as animals, though after a different sort, have a true impregnation and propagation." When Schlegel wrote this, how little could he have imagined the intricacy of this proceeding among the lower forms of vegetation. It has been shewn by Suminski, and verified by many others, that the mode of impregnation, and the period at which it occurs in the ferns, do not at all correspond to the general notion on this subject. He has discovered in the early development of the frond of ferns certain cells, which he denominates antheridia, or sperm cells; these contain in their cavity a number of subordinate cells, each containing a spermatazoon. At a certain period of the progress of the frond, the parent cells become ruptured and liberate the spermatoza, these move about in a mucilaginous fluid, which bedews the inferior surface of the frond, and become the means of impregnating the germ cells, or pistillidia, with which they readily come in contact. Thus the process of impregnation in these plants occurs during the germination, or what corresponds to the period of germination in the seeds of exogenous and endogenous plants.