VII.] TRANSMISSION OF ACQUIRED CHARACTERS. 



4ij 



this by an example. Let us suppose that the influence of 

 climate had caused a plant to change the form of its leaves 

 from an ovate into a lobate shape: now such a change could 

 not be transferred to the germ-plasm in the pollen and the 

 ovules, as anything similar to leaves or the form of leaves ; 

 for such specialized morphological features have no existence 

 in the germ-plasm. The only thing which could happen would 

 be changes in its molecular structure which bear no resem- 

 blance to those changes which arc implied by the direct 

 alteration of the form of the leaf in the parent plant. Any 

 one who clearly appreciates this difficulty will hesitate in 

 admitting the possibility of the transmission of acquired 

 characters, because it is possible that the sexual cells may be 

 affected by correlated influences. If the change in the form of 

 a leaf exercises any influence at all upon the germ-plasm, why 

 should it produce a corresponding (in the above-mentioned 

 sense) change in its molecular structure ? Why should it not 

 produce some other out of the immense number of possible 

 changes ? There must be as many possible changes in the 

 structure of germ-plasm as there are possible variations in each 

 part of a plant that arises from it. Why then should the corre- 

 sponding change always occur, — a change which had never 

 previously existed in the whole phyletic development of the 

 organic world ; for the plant with the latest modification can 

 have never existed before? The occurrence of a particular 

 change out of the countless possible changes would be about as 

 likely as if one out of a hundred thousand pins thrown out of a 

 window were to balance on its point when it reached the 

 ground. The assumption scarcely deserves to be called a 

 scientific hypothesis, and yet it must be made by all who accept 

 the transmission of acquired characters,— that is unless they 

 adopt the hypothesis of pangenesis, which is quite as im- 

 probable, and which even Darwin did not look upon as a real. 

 but only as a formal explanation. 



Detmer is also greatly mistaken when he says that I refuse 

 to admit the transmission of acquired characters, because I am 

 prejudiced in favour of my doctrine of the continuity of the 

 germ-plasm. This doctrine is either right or wrong, and there 

 is no middle course : to this extent I quite admit that I am 

 prejudiced. But the question as to whether acquired characters 



