Page:Treatise on Cultivation of the Potato.djvu/37

 their structures, whence arises the possibility of a multiplication of individual plants by simple subdivision of the vegetative structure of a single specimen—a process which is so frequently and abundantly manifested as to throw the proper reproduction by the seed into the background,—that the duration of herbaceous perennials may be regarded as unlimited, since they are always placed in a position to form new absorbing organs (roots) in the vicinity of their buds." But the buds of the Wellingtonia Gigantea, 300 or 400 feet high, are not in the vicinity of their roots, and the trees have already existed some thousands of years longer than any plants which have been derived from a succession of buds; and when the time comes when the vitality imparted to these derivative plants, and to the Wellingtonia Gigantea, by the sexual union, becomes exhausted, will not the force fail them which has heretofore enabled them to form new absorbing organs? And what does the above quoted phrase, "may be regarded as unlimited," mean? It means "is eternal." The limit of life—the exhaustion of the vital force engendered by the sexual union—is not perceived, and the defective perception is attempted to be concealed by the use of words of an indefinite signification.

It is true, nevertheless, and in an agricultural point of view it is a most important fact, that the original stem dies always, or almost always, many years, possibly thousands, before the plants which have been derived from it by a succession of buds;—and why? Not because these derivative plants have been endowed with an extension of the term of life allotted to the seed from which they and the original plant sprang; for from what source should that endowment come? And not because of the exhaustion of the stock of life of the stem, because the existence of these derivative plants proves that it is not exhausted; but because, as I imagine, of the exhaustion of the supply of food within reach of the roots, perhaps partly because of the noxious action of the excrements of the plant itself, of which the soil surrounding its roots must eventually be almost entirely composed, inconveniences from which the derivative plants, transplanted into fresh soil, are exempt: an exemption which enables them, or some of them, to reach the full term of existence. Also the stem of the old plant becomes in time almost all converted into heart-wood; the circulation of the sap is almost entirely arrested, and this in itself seems sufficient to account for death