144 An Examination of Weismannism. 



supposed to be exercised — provided that it may be 

 so directly, and not necessarily through first having 

 to influence the whole material organism. Therefore 

 I quite agree with Weismann that the facts — sup- 

 posing them to be facts — are quite as explicable by 

 the theory of germ-plasm as by that of pangenesis \ 

 Again, with respect to xenia. Weismann writes : — 



As such eminent botanists as Focke, and more recently 

 De Vries, have expressed much doubt with regard to these obser- 

 vations—or rather interpretations — we must wait until these 

 cases have been critically re-investigated before attempting to 

 account for them theoretically. The chief difficulty we should 

 meet with in any such explanation would be due to the fact that 

 we are here concerned with the influence of the germ-ftlas?n of the 

 sperm-cell on a tissue of another plant which only constitutes 

 a part of this plant. It would thus be necessary to assume that 

 all the determinants of this germ-plasm are not active, and that 

 only those take effect which determine the nature of the fruit. 



Now, it does not appear that De Vries has looked 

 into the matter on his own account, as he merely 

 refers to what Focke has said. And this amounts 

 merely to showing the dubious character of some 

 half-dozen cases which Focke gives as those which 

 alone have fallen within his cognizance. Why he 

 does not mention any of the numerous cases which 

 are quoted by Darwin, I do not understand. Nor 

 can I understand why he does not consider what seem 

 to be the particularly conclusive facts given on 

 p. 80, — i.e., where xenia appears to constitute "a 

 needful preliminary to fertilization." But the whole 

 matter is one for botanists to deal with, and if any 

 doubt attaches to it, at least the grounds of such 

 doubt should be fully stated. Still more, in my 

 1 See Appendix II. 



