70 THE SURVIVAL OF THE UNLIKE. [u. 



germ -plasm is not necessary to the species, or else that 

 it is not localized but distributed throughout the entire 

 body of the individual, as I have shown above ; and 

 either horn of this dilemma is fatal, it seems to me, to 

 Weismannism. If the germ -plasm is not necessary to 

 this reproduction, then we must discard the hypothesis 

 of the continuity of the germ -plasm; if the germ -plasm 

 is distributed throughout the plant, then we are obliged 

 to admit that it is not localized in germ -cells beyond the 

 reach of direct external influences. 



This asexual or vegetative propagation of plants has 

 been brought to Weismann's attention by Strasburger, 

 who cited the instance of the leaf- propagation of 

 begonia, and said that plants thus asexually nmltiplied 

 afterwards produce flowers and seeds, or develop germ- 

 plasm. Weismann meets the objection by supposing 

 that it is possible for "all somatic nuclei to contain a 

 minute fraction of unchanged germ -plasm," but he con- 

 siders the begonia, apparently, to be an exception to 

 most other plants, inasmuch as he declares that "no one 

 has ever grown a tree from the leaf of the lime or oak, 

 or a flowering plant from the leaf of the tulip or con- 

 volvulus." Henslow meets this latter statement by 

 saying that this has not been accomplished simply 

 because "it has never been worth while to do it. If, 

 however, a premium were offered for tulips or oak trees 

 raised from leaf-cuttings, plenty would soon be forth- 

 coming. ' ' What Weismann wishes to show is that the 

 begonia is an exception to other plants in allowing of 

 propagation from leaf- cuttings, although he should have 

 known that hundreds of plants can be multiplied in this 

 way, and that — what amounts to the same thing — all 

 plants can be propagated by asexual parts, as stems or 



