264 Heredity and Eugenics 



substance, even though they are capable of unKmited meta- 

 thetic change in heredity. 



There is another point upon which MacDougal and I 

 differ. MacDougal says, that "his new plants do not 

 hybridize freely, if at all, even when grown with branches 

 interlocking with the parental type," which differs from the 

 conditions which I have found, where intercrossing occurs 

 freely with the parent species. Comparison is difficult 

 between organisms so widely separated as those used by 

 MacDougal and myself, and it is entirely possible that the 

 results of particular processes may result differently in 

 different organisms. 



The results obtained by Gager through the use of radium 

 upon different plants, the modifications of Sempervivum by 

 Klebs, the changes in yeasts and bacteria, etc., can hardly 

 be incorporated at the present time in this discussion in 

 that they have not been carried far enough. Gager 's 

 opinion that the inheritable results obtained by him were 

 possibly due to a disturbance in the chromosome complex, 

 is simply an explanation based upon an old morphological 

 conception. It has not yet been shown that specific chromo- 

 somes are endowed with specific characters resident in 

 them, and until that point is decided definitely the explana- 

 tion of germinal variations on the basis of chromosome 

 behavior must stand aside. 



In animals the experiments of Kammerer, Pshibram, 

 Woltereck, Morgan, and the older experiments of Fischer, 

 Standfuss, Weismann, and others, do not furnish data for 

 a discussion of and far less for a solution of the problem. 

 However, an important point is established by all of these 

 investigations which show uniformly that the germ cells are 

 most susceptible to the influences that produce germinal 



