EFFECTS OF AMPHIMIXIS ON ONl'OGENY 2g'J 



must occur in the individual cells, in which the decision both 

 as regards the preponderance or suppression of certain of the 

 primary constituents, and the number derived from each parent 

 which are to become effective, takes place. For it does not 

 appear to me to be essential that any one of them imist be 

 entirely suppressed, although this will probably occur in most 

 cases. 



If I am not mistaken in my interpretation of a statement 

 made by de Vries, there is no doubt that the primary constitu- 

 ents from both parents may undergo development in one and the 

 same cell. By crossing a red-flowered with a white-flowered 

 species of bean, this observer obtained a hybrid with pale red 

 blossoms, on which the red colouring matter could be recog- 

 nised in solution in the vacuoles of the cells.* If parts only of 

 the cells were coloured, while other parts were colourless, it 

 proves that at least two different (heterodynamous) kinds of 

 biophors. derived from both parents, may control the same cell. 

 There is here, however, an extensive field for further investiga- 

 tion. 



My explanation of the process of mingling of the parental 

 characters is based on the assumption of hereditary units or ids, 

 each of which contains the whole of the ' primary constituents ' 

 of the species, which are, however, modified in the individual. 

 In this connection it may therefore be as well once more to 

 summarise the reasons which lead to this assumption. 



In the first place, such an assumption naturally follows from 

 the view that the germ-plasm is made up of ^ determining parts ' 

 or determinants, for the latter necessitate a definite architecture 

 of the germ-plasm. There must therefore be at least one limited 

 unit of the germ-plasm, to which nothing can be added and from 

 which nothing can be removed without producing an alteration 

 in its capacity for directing ontogeny. But since the process of 

 amphimixis unites the paternal and maternal germ-plasms, each 

 of which contains all the primary constitueiits of the species, each 

 being which is produced sexually must contain at least two ids 

 in its germ-plasm. 



The phenomena of reversion, which will be treated of in 

 greater detail in the following chapter, show that there must be 



* C/; de Vries, I.e., pp. 177, 178. The two species referred to are Pha- 

 seolus jnultijlorus and Phaseolus vulgaris nana. 



