"A. B. Srovur 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 
completely self-sterile. 
The offspring of self-fertile plants were grown for a study of heredity. 
Three families were grown to the second generation (his 13) and two 
Were 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 (A) was 
judged as 0-4 °/, self-fertile; the one plant of the J, was 79°8 °/. self- 
fertile in field isolation ; the self-fertility of the 8 plants of the J, ranged 
from 10 to 68 °/, and that of the 10 plants of the I, ranged from 14°6 to 
a2): ; : 
6—2 
