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Show 344 DARWINIAN A. world, it is clear enough that a common plant or tree is not an individual in the sense that a horse or man, or any one of the higher animals, is-that it is an individual only in the sense that a branching zoophyte or mass of coral is. Solvitur crescendo : the tree and the branch equa1ly demonstrate that they are not individuals, by being divided with impunity and advantage, with no loss of life, but much increase. It looks odd enough to see a writer like Mr. Sisley reproducing the old hypothesis in so bare a form as this : "I am prepared to maintain that varieties are individuals, and that as they are born they must die, like other individuals. . . . We know that oaks, Sequoias, and other trees, live several centuries, but how many we do not exactly know. But that they must die, no pne in his senses wiJl dispute." Now, what people in their senses do dispute is, not that the tree will die, but that other trees, established from its cuttings, will die with it. But does it fo1low from this that non-sexuallypropagated varieties are endowed with the same power of unlimited duration that is possessed by varieties and species propagated sexuaJly-i. e., by seed~ Those who think so jump too soon at their conclusion. For, as to the facts, it is not enough to point out the diseases or the trouble in the soil or the atmosphere to which certain old fruits are succumbing, nor to prove that a parasitic fungus (Peronospora infesta;ns) is what is the matter with potatoes. For how else would constitutional debility, if such there be, more naturally manifest itself than in such increased .liabi:ity or diminished resistance to such attacks~ And 1f you say that, anyhow, such varieties do not die of old age DURATION OF RACES. 345 -meaning that each individual attacked does not die of old age, but of manifest disease-it may he asked in return, what individual man ever dies of old age in any other sense than of a similar inability to resist invasions which in earlier years would have produced no noticeable effect~ Aged people die of a slight cold or a slight accident, but the inevitable weakness that attends old age is what makes these slight attacks fatal. Finally, there is a philosophical argument which tells strongly for some limitation of the duration of . non-sexually-propagated forms, one that probably Knight never thought of, but which we should not have expected recent writers to overlook. When Mr. Darwin announced the principle that cross-fertilization between the individuals of a species is the plan of Nature, and is practically so universal that it _fairly sustains his inference that no hermaphrodite species continually self-fertilize9. would continue to exist, he made it clear to all who apprehend and receive the principle that a series of plants propagated by buds only mur:;t have weaker hold of life than a series reproduQed by seed. For the former is the closest possible kind of close breeding. Upon this ground such varieties may be expected ultimately to die out; but " the mills of the gods grind so exceeding slow" that we cannot say that any particular grist has been actually ground out under human observation. If it be asked how the asserted principle is proved or made probable, we can here merely say that the proof is wholly inferential. But the inference is drawn from such a vast array of facts that it is wellnigh irresistibl~. It is the legitimate explanation of |