122 Plant Genetics 



by investigating and controlling all kinds of inheritance. 

 No more favorable material for determining the funda- 

 mental facts of inheritance can be found among plants 

 than the spores of the simpler forms. They are accessible 

 and therefore capable of control; a succession of spore- 

 produced individuals represents a line whose purity can- 

 not be questioned; the so-called "modification of the 

 germ plasm" can be accomplished with a precision that 

 is impossible in the case of an egg nucleus within an 

 ovule and an ovary. In short, free from all the entangle- 

 ments of sex, the possibilities of variations in pure lines 

 can be determined and the possibilities of inheritance 

 of such variations. Such observations will establish the 

 facts common to all inheritance and will enable us to 

 recognize the contribution of sex to inheritance. 



This is no criticism of the work that has been done 

 with seed plants. That work was the natural beginning 

 and the results have been remarkable. It is simply 

 calling attention to the necessary limitations of experi- 

 mental work in genetics with seed plants and the desira- 

 biUty of extending the field of genetics so as to include 

 the lower forms that will permit certain desirable 

 things to be done with greater exactness. 



1. Pace, Lula, Apogamy in Atamosco. Bot. Gaz. 56:376-394. 

 pis. 13, 14. 1913. 



2. Yamanouchi, Shigeo, Apogamy in Nephrodium. Bot. Gaz. 

 45:289-318. pis. Q, 10. 1908. 



