Bearers of Hereditary Characters 203 



quote from Wilson (3): "For the present, at least, all 

 the requirements of investigation are met if we think of 

 the chromosomes, or that which they carry, only as 

 differential factors in heredity, not as primary or exclusive 

 'determiners.'" It is a very dominant conception in 

 biology today that all plant and animal phenomena are 

 to be explained ultimately on a physico-chemical basis. 

 Cytology, therefore, should not be satisfied with observ- 

 ing and recording the peculiar contortions of chromo- 

 somes in their different phases. Such a study is justified 

 only in so far as it furnishes some useful working hy- 

 potheses. The ultimate thing to be striven for is to be 

 able to control plants and animals artificially, and this 

 can be done only by understanding the physics and 

 chemistry that underlie the chromosomes as well as all 

 other life-phenomena. 



With this presentation of the arguments for and 

 against the chromosome hypothesis of inheritance, a 

 conclusion seems to be difficult, but a suggestion may be 

 made that seems reasonable and may be useful. That 

 chromosomes are the visible bearers of hereditary char- 

 acters is probably true, at least in most cases upon which 

 there are data. Chromosomes, however, are not the 

 ultimate things; behind lies the physico-chemical 

 background, and it is this which is the ultimate aim 

 of biology to understand. 



Such a statement may seem unsatisfactory. It has 

 been said that chromosomes determine sex in some cases 

 and that physiological conditions determine sex in other 

 cases; then it was inferred that the same may be true of 

 other plant characters as well. Can we not unify these 

 two alternative conclusions in some single theoretical 



