But since the function creates the organ, and where function is not localized there is no variation of parts, life probably began in formless combinations having no visible distinction of parts. And as the cell is the first step in organization, it is the fundamental structure of living things, “it marks only where the vital tides have been or how they have acted,” the lowest organisms consisting of one cell only, and the higher consisting of many cells, which, increasing in complexity or diversity of form adapted to their different functions at later stages, are modified into the special tissues, with resulting unlikeness in parts or organs, of which all plants and animals are composed. Every variation in structure is, therefore, due to cellular changes, and every living thing is propagated in one way or another by cells, by their self-division or multiplication; or by gemmation, _i. e._, throwing off buds; or by the union of like cells; or, in more complex mode, by the spontaneous or aided union of unlike cells, as the sperm-cell of the male with the germ-cell of the female, giving rise to a seed or egg from which grows offspring more or less like its parents. In both plant and animal the cell-contents usually, although here again exceptions occur in some of the lowest organisms, exhibit a rounded body called the _nucleus_, which itself often incloses another body called the _nucleolus_, the functions performed by both of which in cell development are obscure. That even thus much is known of cell structure may awaken wonder when it is remembered that we are dealing with bodies for the most part beyond the range of our unaided vision. Bacon truly says that “the complexity of nature exceeds the subtlety of man”; the infinite divisibility and indivisibility of matter is apparent in the organic as in the inorganic; and size counts for little; the oak and pine, the acacia and the rose, are lower in scale of life than the thistle and the daisy; the elephant is 150,000 times heavier than the mouse, but the egg of the one is nearly as large as that of the other, and it has been calculated that if one molecule in the nucleus of the ovum of a mammal were to be lost in every second of time, the whole would not be exhausted in seventeen years. These molecules are the sufficing material media of transmission of resemblances, both striking and subtle, between parent and offspring; and of the vast sum total of inherited tendencies, good or bad, which are the product of no one generation, but which reach us charged with the gathered force of countless ancestral experiences. “Born into life! man grows Forth from his parents’ stem, And blends their bloods, as those Of theirs are blent in them; So each new man strikes root into a far fore-time.” CLASSIFICATION OF PLANTS --LOUIS FIGUIER