20 HEREDITY. 



crosses the inheritance of certain characters is exclusively 

 through the mother, and that no segregation occurs at the time 

 of gamete formation. The fact that in those instances, we are 

 concerned with the transmittance of extra-nuclear material 

 (colour of the cotyledon of soy-beans) certainly points to the 

 cell-nucleus as to the organ responsible for Mendelian segrega- 

 tion. And, if inside the nucleus, we see such a very complicated 

 process as karyokinesis, and such significant modifications of 

 the process at the moment of production of germ-cells, all the 

 circumstantial evidence certainly points to the conclusion, 

 that the chromosomes are ultimately bound up with the pro- 

 cess, which leads to a distribution of genes over cell-generations. 

 Wehestitate to go further, and declare with so many authors, 

 to believe the chromosomes to be the bearers of heredity. In 

 these matters it is extremely difficult to see clearly, what is 

 cause and what is effect, what is of primary and what of second- 

 ary occurrence. Cytology, microscopic Technique and Mor- 

 phology are certainly ahead of Bio-chemistry of the cell, of 

 Micro-chemistry. But this admittance need not bring us to the 

 point, where we attach more importance to the more complete 

 morphological evidence than to the chemical facts, which are 

 obtained with so much more difficulty. The striking pictures 

 which Cytologists select for us from among their tens of thou- 

 sands of stained sections of cells, certainly ought not to make 

 us sceptical concerning the chemical processes which we can 

 not see or make visible, but which assuredly accompany and 

 possibly cause the morphologic phenomena. 



There is no incompatibility between the view, that the genes 

 are of a relatively simple chemical nature, and that they are in 

 someway localized on, or in, the chromosomes, but no one who 

 has read Trow's criticism of the evidence of "crossing over" 

 can prevent himself from being ever afterward rather sceptical, 

 when confronted with evidence for the localization in the Nth 

 locus on the Pth chromosome of a certain gene. 



In this connection we may not forget, that the number of 

 genes we can study in any group of organisms is necessarily 



