202 Plant Genetics 



appeal to many of the most prominent physiologists and 

 physiological chemists. 



(2) Physiological chemists claim that chromosomes 

 in all plants are chemically identical. If chromosomes 

 differ so much in the factors they carry, one should 

 expect them to show some chemical differences in the 

 various races of plants, but they show no such differences. 

 On the other hand, there are other plant constituents 

 that show a remarkable chemical specificity. Plant 

 proteins, for example, are chemically different in about 

 every plant species. Plant starches, also, have been 

 shown to be pecuhar in their chemical constitution to 

 the race of plants in which they occur. It is natural 

 to ask why are not these proteins and starches, with 

 their remarkable specificity, more like what the carriers 

 of hereditary characters ought to be than the chromo- 

 somes which are chemically the same throughout the 

 plant kingdom. 



(3) Such work as that of Riddle is directly against 

 the chromosome hypothesis. If it is found that char- 

 acters which were supposed to be determined by chromo- 

 somes can be controlled artificially by regulating the 

 physiological conditions, it makes one conclude that 

 chromosomes are not of controlhng importance in 

 inheritance. 



(4) Finally, there is the growing impression that 

 chromosomes are consequences instead of causes. 

 Instead of actually determining hereditary characters, 

 chromosomes may well be merely a rather useful super- 

 ficial index of the hereditary situation. It may be that 

 this is all the claim made for the chromosome hypothe- 

 sis by many cytologists. In this connection we may 



