14 THE GERM-PLASM 



arising from it was not supposed to exist by any one at that 

 time, nor does it do so except in isolated cases. The ' transport 

 hypothesis ' was therefore also necessary in order to explain the 

 production of germ-cells of each kind, which must again contain 

 the gemmules of the parents. (^alton, who also rejected the 

 ' transport hypothesis,- thus found himself in the peculiar posi- 

 tion of being obliged to suppose that the germ-cells which the 

 organism produces can only contain the unused remainder of 

 the gemmules and their successors, i.e.^ those gemmules which 

 had been unable to take part in the construction of the organism, 

 and which had remained dormant and were individually of ? 

 different nature from the other gemmules. He made use of this 

 supposition to explain the difference between children of the 

 same parents, but found himself obliged to resort to a very 

 artificial assumption to account for the main problem of the 

 resemblance between such children and their parents. 



That part of Darwin's theory which de Vries retains is the 

 existence of an hereditary substance composed of ' gemmules,'' or 

 minute vital particles which are capable of growth and multi- 

 plication by fission, and which become active consecutively in 

 ontogeny, and so build up the organism. The theory is thus 

 deprived of, its merely speculative elements, and by transferring 

 the gemmules, in accordance with the most recently ascertained 

 facts, to the germ substance, which, as we know, is passed on 

 by division from cell to cell, the theory of pangenesis is placed 

 on a firm footing. 



De Vries, however, was not content with simply modifying 

 Darwin's theory of pangenesis in a negative manner, by doing 

 away with one — almost the greater — portion of it; he also 

 reformed it positively by giving a new meaning to the ' gem- 

 mules.' There is an essential difference between Darwin's 

 gemmules of cells, and de Vries's pangenes, which are gemmules 

 of elements much smaller than cells — that is to say, of the 

 smallest parts of which a single cell is composed. These pan- 

 genes are the bearers of the individual qualities or ' characters ' 

 of the cell. 



The train of thought which led de Vries to imagine the con- 

 struction of the hereditary substance from such ' bearers of the 

 qualities' (' Eigenschaftstrager ') of the cells is too interesting to 

 be passed over. He bases this idea on the assumption of ' a 

 mutual independence of the hereditary qualities, ' According to 



