Weismann s theory of Heredity (1891). 53 



ductivc efficiency throughout the general tissues of 

 the organism, Weismann cannot refrain from taking 

 the further step of supposing that the germ-plasm, 

 like the gemmules of Darwin, is capable of any 

 amount of multiplication in the general cellular tissues 

 of plants — seeing that plants can be propagated by 

 cuttings, buds. &c, indefinitely. And this, as we have 

 seen, Professor Weismann, in his second essay, does 

 not shrink from doing. Moreover, although I cannot 

 remember that he has anywhere expressly said so. it 

 is obvious that the allied phenomena of regeneration 

 and repair admit of explanation by his hypothesis 

 of " ontogenetic grades," after the manner already 

 stated in Chapter II. Indeed, it is evident that in 

 no other way can these phenomena be brought 

 within the range of his theory. But from this it 

 follows that not only in the case of organisms which 

 are capable of somatic reproduction is the formative 

 nucleo- plasm (idio-plasm-B) diffused throughout the 

 somatic-tissues : on the contrary, it must be univer- 

 sally diffused throughout all the somatic-cells of all 

 living organisms ; and whether as it there occurs it is 

 capable of reproducing entire organisms, single organs, 



plants ; but it is certainly much greater than Weismann supposes. 

 " How is it that all plants cannot be reproduced in this way? '' he asks, 

 and then adds, — "No one has ever grown a tree from the leaf of a lime 

 or an oak, or a flowering plant from a leaf of the tulip or the 

 convolvulus." But I am told by botanists that the only reason why 

 the phenomenon thus appears to be a rare one, is because it is not 

 worth anybody's while to grow plants in this way at a necessarily 

 unsuitable season of the year. Thus, the Rev. George Henslow 

 writes me: — "The fact is that any plant will reproduce itself by its 

 leaves, provided that the cells be 'embryonic,' (i.e., the leaf not 

 too near its complete development), and that it be not too thin, 

 so as to provide enough nutriment for the bud to form till it has 

 roots." 



