360 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



tive constancy and purity. It is also clear that the assignment of 

 different and independent degrees of influence in the development 

 of sterility to the various assumed units would theoretically 

 account for any sort of fluctuation or variation in the individual 

 development of self-fertility. Such explanations, however, do not 

 add to the understanding of the actual chemical and physiological 

 processes and only very indirectly to the practical problems of 

 the effects of inbreeding and the development of highly self-fertile 

 races. It would appear also that this view limits the constitutional 

 differences to hereditary elements quite independent of any cyto- 

 plasmic relations that may exist, which in this respect is in accord 

 with the conception of Baur and Correns and Compton, but not 

 agreeing with the views of Darwin and Jost and Morgan. If this 

 be true, it is not clear why somatic cells of the pistil cannot react 

 favorably with pollen tubes if the former possess some element 

 different from the pollen; but as such a relation always exists and 

 most especially so with hybrids such as East reports, there would 

 be, from this basis, universal self-fertility. 



East assumes that the tobacco hybrids are self-sterile because 

 none of the pollen grains produced by a plant possess any heredi- 

 tary element not present in the somatic cells of that plant. But no 

 pollen of a plant ever does, unless there are vegetative mutations, 

 segregations, or other variations among the branches and among 

 the pistils and stamens of a plant, so the conception fails to account 

 for self-fertility, especially of lines breeding true, which is a wide- 

 spread phenomena in plants and which East has repeatedly in- 

 sisted is the rule in Nicotiana species. 



From the reviews just given, it is evident that intensive studies 

 regarding the facts of cross- and self-incompatibility in plants 

 have been attempted only in the two cases reported by Correns 

 and East, and that even in these cases much desirable data were 

 not obtained. It is very obvious that before we can arrive at any 

 comprehensive conception of the principles involved, much more 

 evidence is needed. It is with especial reference to such data that 

 the writer here presents the results of studies with chicory (Ci- 

 chorium Intybiis) which j^ertain to the expression and the heredity 

 of physiological self- and cross-incompatibility. 



