A. B. Strout 125 
to a conception of multiple factors directly concerned with the trans- 
mission and expression of incompatibilities this must necessarily be a 
result in inbreeding or line-breeding. East and Park (1918) assume 
that this is true for cross-incompatibility. The evidence from chicory 
shows conclusively that repeated self-fertilization in line-breeding does 
not lead to an increase of self-incompatibility. The average self-fertility 
of a race may be maintained very uniformly under repeated self- 
fertilization. No tests for cross-incompatibility were made in those 
families of chicory for which new data are reported above. It may be 
stated, however, that all the self-incompatible plants produced an 
abundance of seed to open cross-pollination which could only have been 
between sister or closely related plants of the variety red-leaved Treviso. 
Thus far the studies of self- and cross-incompatibilities have been in 
species in which the incompatibilities were already present as a character 
variable in constitutional or genetical value. No one has observed the 
origin of such a condition in a species. No one has produced such a 
condition experimentally. Numerous excellent studies have been made 
(see especially Kraus and Kraybill, 1918) of the influence of various 
conditions of nutrition on vegetative and reproductive vigour. Plants 
of highly self-fertile species have been rendered sterile and fruitless 
but in such cases the plant was fully sterile. It not only failed to set 
fruit to self-pollination but*to all cross-pollination as well. The sterility 
was not relative, it was indiscriminate and absolute. 
The evidence therefore that conditions of incompatibility are not 
directly induced by repeated self-fertilization, and are not to be ascribed 
to the condition of hermaphroditism as such, is further proof that variation 
is operating in the physiological sex differentiation of sex organs. 
3. Variations in morphological sex differentiation, especially recog- 
nized as phenomena of intersexualism, occur frequently in species 
prevailingly either hermaphrodite or dioecious, and are quite analogous 
to those variations in physiological differentiation revealed by incompati- 
bilities, 
Concerning the relation between seed-sterility from incompatibility 
and sterility from various types of impotence there is much need of 
further information, In general the two classes are distinct. Incom- 
patibility operates between sex organs either of the same hermaphrodite 
or of different individuals which are highly functional in certain relations. 
It is characteristic of self-incompatible and cross-incompatible plants — 
that the respective sex organs may be fully developed and potent. ; 
Many cases of pollen and embryo sac development are associated 
