Page:Popular Science Monthly Volume 43.djvu/498

482, we here find that agamogenesis may go on without end. Numerous plants and trees are propagated to an unlimited extent by cuttings and buds; and we have sundry plants which can not be otherwise propagated. The most familiar are the double roses of our gardens: these do not seed, and yet have been distributed everywhere by grafts and buds. Hothouses furnish many cases, as I learn from an authority second to none. Of "the whole host of tropical orchids, for instance, not one per cent has ever seeded, and some have been a century under cultivation." Again, we have the Acorus calamus, "that has hardly been known to seed anywhere, though it is found wild all over the north temperate hemisphere." And then there is the conspicuous and conclusive case of Eloidea Canadensis (alias Anacharis) introduced no one knows how (probably with timber), and first observed in 1847, in several places; and which, having since spread over nearly all England, now everywhere infests ponds, canals, and small slow rivers. The plant is diœcious, and only the female exists here. Beyond all question, therefore, this vast progeny of the first slip or fragment introduced, now sufficient. to cover many square miles were it put together, is constituted entirely of somatic cells; and this cell-multiplication, and consequent plant-growth, show no signs of decrease. Hence, as far as we can judge, these somatic cells are immortal in the sense given to the word by Prof. Weismann; and the evidence that they are so is immeasurably stronger than the evidence which leads him to assert immortality for the fissiparously-multiplying Protozoa. This endless multiplication of somatic cells has been going on under the eyes of numerous observers for forty odd years. What observer has watched for forty years to see whether the fissiparous multiplication of Protozoa does not cease? What observer has watched for one year, or one month, or one week?

Even were not Prof. Weismann's theory disposed of by this evidence, it might be disposed of by a critical examination of his own evidence, using his own tests. Clearly, if we are to measure relative mortalities, we must assume the conditions the same and must use the same measure. Let us do this with some appropriate animal—say Man, as the most open to observation. The mortality of the somatic cells constituting the mass of the human body is, according to Prof. Weismann, shown by the decline and final cessation of cell-multiplication in its various organs. Suppose we apply this test to all the organs: not to those only in which there continually arise bile-cells, epithelium-cells, etc., but to those also in which there arise reproductive cells. What do we find? That the multiplication of these last comes to an end long before the multiplication of the first. In a healthy woman, the cells which constitute the various active tissues of the body continue to grow