CROSSING. 67 



he offered a "Grundfactor-Supplement Theorie". If we sub- 

 stitute "residual genotype" for Plate's "base-factor" his hy- 

 pothesis is in full accord with ours. If two organisms have an 

 identical set of genes with the exception that one has an addit- 

 ional gene, we have no great objection to calling this gene a 

 "supplement." But no matter how we call things, we can have 

 only a faint idea of the complexity of the whole development, 

 up to the point where the presence of the gene under discus- 

 sion makes itself felt. What we should do, is to try to study the 

 way, in which a gene does affect the development, and thus, 

 in the language of the Weismann-Mendelians "determines its 

 unit-character". 



The cases in which we happen to know three or six genes 

 which all influence the same quality of an organism, may 

 seem more complicated than the cases, in which we know of 

 only one. They are certainly more difficult to analyse. If we 

 know from Nilsson Ehles work, that there are at least three 

 genes in wheat which tend to deepen the red colour, whereas 

 we know of only one gene in wheat which tends to make the 

 colour black, this does not mean, that the processes which 

 ultimately lead to the production of red giain are any more 

 complex than those which produce black grain. 



Many of the Geneticians still hold to the Weismannian idea 

 of determinants for characters, and to them the genes are 

 transmitted things which are in themselves responsible in some 

 way for definite characters. They think with Castle that it 

 would be theoretically possible to "analyse the characters of 

 an organism into the component units." This conception of 

 characters of organisms as things in themselves, and of organ- 

 isms as mosaics of charcters has unavoidably grown out of 

 the circumstance that the "rediscovery" of Mendel's work by 

 Correns and Tschermack came just at the right time to dove- 

 tail in with de Vries' revival of Darwin's pangene- theory. 

 Further, just when de Vries had set forth his conception of in- 

 heritance as the transmission of numerous different pangenes, 

 each responsible for a character, and his belief that evolution 



