120 Self-Incom^mtihility in Hermaphrodite Plants 



Discussion and Conclusion. 



It seeins clear that both self- fertility and cross-fertility within a 

 species are original and primitive conditions as compared with self- 

 incompatibility and cross-incompatibility. Further it seems clear that 

 self- fertility is more primitive than cross-fertility just as hermaphro- 

 ditism is obviously the more primitive condition out of which dioecism 

 has developed.. In hermaphrodites incompatibilities have arisen in 

 species, and evidently are arising at the present time, through fluc- 

 tuating variation in the physiological differentiation of the sex organs. 

 These phenomena run parallel to the anatomical variations leading to 

 intersexualism and dioecism. 



The evidence supporting this general conclusion from my own studies 

 and from the facts revealed by other recent studies as well may here be 

 summarized under the following heads : 



1. The indisputable evidence that compatibility and incompati- 

 bility in many species are highly variable both in expression and in 

 heredity. 



2. The evidence is conclusive that self-incompatibility is not always, 

 if ever, induced by self-fertilization and inbreeding. 



3. Variations, now recognized as phenomena of intersexualism, in 

 morphological sex differentiation in species which are prevailingly 

 hermaphrodite or dioecious, are quite analogous to variations in physio- 

 logical differentiation. 



4. The obvious conclusion is that sex differentiation and determina- 

 tion, and hence compatibility and incompatibility in hermaphrodites, are 

 fundamentally of ontogenetic and biogenetic development. 



1. The evidence is conclusive that in the various so-called self- 

 incompatible homomorphic species there are individuals that are to 

 some extent self-compatible, and that there is among these wide 

 variability as to the number of sex organs that will function together. 

 This is true at least of nearly all species whose self-fertility has been 

 studied. The same general conditions are found in cases of cross- 

 incompatibility within such species. Even reciprocals between pairs 

 of plants may give opposite results. 



As a rule feeble or partial compatibility manifests itself quite 

 indiscriminately throughout the entire period of bloom. Marked cases 

 of a periodic change in compatibility do occur such as end-season 

 self- fertility (in Nicotiana Forgetiana Hyb. Hort. and in Lythrum 



i 



