PRESIDENTIAL ADDRESS — SECTION D. 181 



It is simply inconceivable that there should be scattered 

 through the nuclei of the leaves of a Begonia, or the epidermal 

 cells of a Bryozoan, particles of matter which are at the same 

 time completely cut off from the action of the influences that 

 affect the rest of the substance of the nuclei in which they are 

 lodged; and yet this is the demand which Weismann's theory 

 of the continuity (in an unaltered and unalterable form) 

 of the germ-plasma makes of our credulity. The su23posed 

 continuity and unchangeableness of the germ-plasm rests on 

 its presumed isolation. When it is shown that in most of the 

 lower and some of the higher plants and animals there is no 

 such isolation, the whole doctrine, to my mind, necessarily falls 

 to the ground. 



Closely connected with his theory of the continuity of the 

 •germ-plasma is the explanation wdiich Weismann offers of the 

 occurrence of variation in organisms. This, he holds, is due 

 to two main causes — firstly, differences existing in the mature 

 ■sexual cells ; secondly, differences which result from impregna- 

 tion. The first set of differences are due to the probable com- 

 plexity of minute structure in the nuclei of the germ-cells — a 

 complexity so great that it is unlikely that division could take 

 place twice in precisely the same way, so that, to start with, no 

 two ova or spermatozoa are precisely alike. The second cause 

 of difference is the combination of the germ-plasmata of two 

 different individuals ; and this Weismann supposes to be the 

 meaning of the process of sexual reproduction : " Sexual repro- 

 duction has arisen, and holds its own, as the chief mode of 

 reproduction in both kingdoms of organic nature because by 

 means of it varieties are produced which form the material on 

 Avhich natural selection acts." 



That sexual reproduction may be a cause of variatioii is 

 highly probable ; it is difficult to see how it can be the cause 

 of the appearance of an entirely new^ character, for it can only 

 ■effect combinations and recombinations of what has already 

 •existed. It certainly is not the cause of all variation, as 

 Weismann has himself now acknowledged. 



It is a familiar fact that in the case of some of the most 

 •widely cultivated garden plants, such as the roses and chry- 

 santhemums, which present almost innumerable variations, 

 .and in which new varieties are constantly making their appear- 

 ance, there is no question of sexual reproduction at all, as 

 propagation of new varieties is effected entirely through the 

 medium of cuttings. Full details of these phenomena of " bud- 

 variation " are given by Darwin in his " Variation of Animals 

 and Plants under Domestication," and it is very singular tliat 

 these very significant facts should have been completely over- 

 looked by one professing to be a critic of Darwin and his 



