TRANSMISSION OF ACQUIRED CHARACTERS. 401 



so far from lending any support to the assumption that acquired 

 characters can be transmitted, Detmer's experiment rather tends to 

 disprove this opinion. 



I think I have sufficiently shown that Detmer's reproach that 

 I have under-estimated the effects of external influences upon an 

 organism may be fairly directed against its author. If we can 

 believe that every structural arrangement in plants, which depends 

 upon certain external conditions, has been produced in a phyletic 

 sense by these latter, it becomes very easy to explain the trans- 

 formation of species ; but in accepting such an explanation we 

 are building without any foundation, for the proof that acquired 

 characters can be transmitted has yet to be given. 



As a further disproof of my views Detmer quotes the so-called 

 phenomena of correlation in plants, and he believes that these 

 instances help us to conceive how the acquired changes of the body 

 (soma) of the plant may also influence the sexual cells. If the 

 apical shoot of a young spruce fir be cut off, one of the lateral 

 shoots of the whorl next below the section rises and becomes an 

 apical shoot : it not only assumes the orthotropic growth of such 

 a shoot, but also its mode of branching. The phenomenon itself is 

 well known, and I have often observed it myself in my garden 

 without making any botanical experiments ; for this experiment 

 is not uncommonly made by Nature herself, when the apical 

 shoot is destroyed by insects (for example the gall-making 

 Chermes). The change of the lateral into an apical shoot occurs 

 here in consequence of the loss of the true apical shoot, and is 

 therefore really dependent upon it. The only difficulty is to 

 understand how these and many other kindred phenomena can 

 be considered to prove the transmission of acquired characters. 

 That correlation exists between the parts of an organism, that cor- 

 related changes are not only common but nearly always accompany 

 some primary change, has been perfectly well known since Darwin's 

 time, and I am not aware that it has been disputed by any one. I 

 further believe that hardly any one would maintain that it is im- 

 possible for the reproductive organs to be influenced by correlation. 

 But this is very far from the admission that such changes would 

 occur in the germ-cells as would be necessary for the transmission 

 of acquired characters. For such transmission to occur it would be 

 necessary for the germ-plasm (the bearer of hereditary tendencies) 



Dd 



