stout: pollinations in cichorium: intybus 449 



incompatibility, from strains previously fully self-fertile has not 

 been observed in cultures or produced either by inbreeding or by 

 wide crossing, showing that it is quite in the category of such 

 deep-seated characters as those of heterostyly and proterandry, 

 and such sex differentiation as that of individuals as wholes. 

 East's ('15a) results with tobacco are most suggestive of the 

 origin of self-sterility through crossing, but as he is inclined to 

 consider the parent species as also somewhat self-sterile, this point 

 is in doubt in this case. Still the production of types of impotence 

 by wide crossing is proverbial, and we may find that the production 

 of self-sterility due to physiological incompatibility is equally 

 frequent. Impotence is no more directly and simply hereditary 

 in outcrosses than is self-sterility. As in chicory, all known cases 

 of sterility from physiological incompatibility have been studied 

 only in species and strains in which it was already well developed, 

 at least to the extent that some plants were thus self-sterile. 



It must be fully recognized that the wide variations in the 

 expression of incompatibility through sterility may, to a marked 

 degree, mask the underlying tendencies of development. This is 

 especially true when we consider the behavior of sterility and 

 fertility in heredity. In my cultures of chicory self-fertile plants 

 arose from self-sterile parents. The study of the offspring of such 

 plants gives direct evidence on the heredity of the characteristic 

 of self-fertility immediately after its appearance in a line of descent. 

 The tendency is strong for complete self-sterility to develop among 

 various individuals of the offspring of these self-fertile parents: 

 but on the other hand there is a nearly equal tendency for self- 

 fertility to develop among such offspring. These two tendencies 

 illustrate what may be called the inertia of cell organization as 

 expressed in heredity. The particular somatic conditions in an 

 individual and the particular grade of sex differentiation are not 

 fully transmitted through spore formation and the formation of a 

 new zygote. No doubt this sporadic nature of the character is 

 chiefly due to the fact that the particular type of organization and 

 differentiation which existed in the parent is not duplicated in the 

 various offspring. The agreement is, however, sufficient to main- 

 tain a marked degree of fertility. On the other hand the varia- 

 tions are sufficient to give constant fluctuations in self-fertility 

 about a rather fixed mode. To what extent the mode in chicory 

 30 



