6 Plant Genetics 



species by natural selection does not call for the inherit- 

 ance of acquired characters. 



The theory of pangenesis proper is quite in keeping 

 with the present point of view; but the weakness of 

 the transportation hypothesis was so evident that it 

 was soon set aside by biologists. In discarding the 

 transportation hypothesis, however, biologists in general 

 rejected also the doctrine of pangenesis, a common result 

 when a truth is found in combination with the obviously 

 false. 



The theory of heredity which was chiefly responsible 

 for replacing pangenesis was proposed by WEISMANN (3), 

 whose publications appeared during the decade 1880- 

 1890. WEISMANN developed two companion theories: 

 one called germinal continuity, which has to do with 

 heredity; and the other called germinal selection, 

 which is a very imaginative explanation of individual 

 variation. Our concern is chiefly with the theory of 

 germinal continuity. 



According to DARWIN'S transportation hypothesis, 

 any change arising in the organism at any time during 

 its life would become represented by gemmules in the 

 reproductive cells. In this way it would be possible for 

 acquired characters to be inherited. WEISMANN could 

 discover no mechanism in plants or animals which could 

 justify such a conception. 



It had been known for some time that germ cells and 

 body cells in animals remain separate during their later 

 development, but WEISMANN seems to have been the 

 first to point out the significance of this fact. He makes 

 the following statement: "The difficulty or the impos- 

 sibility of rendering the transmission of acquired char- 



