AND THE LOWER ANIMALS. 273 



quently, after a longer or shorter lapse of time, repro- 

 duction by seeds becomes necessary; therefore, in 

 plants as in animals, this alone is a function of the 

 first class, whilst agamic reproduction is but a sub- 

 ordinate office. It is almost idle to comment on the 

 harmony existing in this respect between facts and 

 our theoretical deductions, at least in regard to plants 

 in a state of nature.* 



We see then that these cycles of reproduction which 

 Steenstrup first pointed out in animals, appear in 

 plants also. In both kingdoms these cycles commence 

 by the development of an ovum or a fertile seed, 



* The artificial propagation of vegetables by cutting, laying, 

 and grafting, constitutes a true process of multiplication by genea- 

 genesis. Is this process applicable indefinitely ? This question 

 which was put in the last century, has been answered in various 

 ways. Knight went so far as to say that the life of individuals 

 produced by different methods could not exceed in length that 

 of the parent from which the graft, slip, bud, &c, was taken. — 

 (Chevreul's report on Count Odart's work entitled " Ampelogra- 

 phie.") M. Puvis, while opposing Knight's evident exaggerations, 

 partly embraced his opinions, and applied to animals in general, 

 and to man himself, the views which Chevreul justly refuted; But 

 is not the exclusive employment of these various modes of repro- 

 duction likely to result in the general deterioration or exhaustion 

 of the individuals thus obtained ? All that we have learned in 

 these essays on geneagenesis, forces me to reply in the affirmative. 

 Moreover I have heard that M. Cosson maintains this opinion, 

 which he supports very ably on facts borrowed from the history of 

 cultivated plants. It is to the abuse of the geneagenetic method of 

 reproduction that this distinguished botanist attributes, at least 

 in part, those general diseases which commit such havoc among 

 our plants ; it is to the same cause also that he refers the gradual 

 disappearance of the weeping willow (Salix Babylonica), formerly 

 so very common, but of which there are now in Europe only a few 

 female individuals, which it becomes more and more difficult to 

 reproduce by cuttings. 



T 



