A. B. Stout 87 



2. There is evidence for considering that in some cases at least 

 embryo abortion is due to physiological incompatibility. 



3. The behaviour of further pedigreed progenies of self-compatible 

 parentage in chicory shows that repeated selection does not eliminate 

 the extreme fluctuations though tending toward the establishment and 

 maintenance of highly self-fertile races, 



4. Continued self-fertilization in chicory has not led to a decrease 

 in the self-compatibility that exists in any given line and has not given 

 general evidence of decrease in vegetative vigour. 



5. All the results favour the view that incompatibilities arise 

 primarily in the ontogenetic processes of physiological differentiation of 

 sex organs, and are not determined by either individual stuffs or line 

 stuffs of definite hereditary value. As far as general constitution is 

 concerned similarity in parents favours fertility. In respect to the 

 ontogenetic processes of sex differentiation the results may be taken as 

 evidence that successful fertilization depends fundamentally on the 

 element of similarity. 



Review of the more Recent Literature bearing on 

 Physiological Incompatibility in Fertilization. 



The more recent report of studies with rye (Heribert-Nilsson, 1916) 

 favours the doctrine that self-incompatibility is a relative quality rather 

 than that any individual, or any race of this species, is absolutely 

 self-incompatible. Heribert-Nilsson finds, in general agreement with 

 previous investigators, that rye is decidedly self-sterile. Highly self- 

 fertile and feebly self-fertile individuals are however to be found in 

 any population, and he questions whether any plant of rye is really 

 coiApletely self-sterile. 



The offspring of self-fertile plants were grown for a study of heredity. 

 Three families were grown to the second generation (his I3) and two 

 wei-e continued into the third generation. One family which was the 

 largest in regard to the numbers grown and tested (8 plants in the 

 second and 10 in the third generation) maintained a rather high grade 

 of self-fertility, and all plants were self-fertile. The parent (/i) was 

 judged as 0-4% self-fertile; the one plant of the I^ was 79-8 7„ self- 

 fertile in field isolation ; the self-fertility of the 8 plants of the L, ranged 

 from 10 to 68 °/^ and that of the 10 plants of the /^ ranged from 14-6 to 

 74-1%. 



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