A. B. Stout 95 



When the first self-fertile plants appeared in my cultures, I was of 

 the opinion that the characteristic of self- fertility would be decidedly 

 discontinuous, and that it would be transmitted as a fixed quality. In 

 other words, it was thought that the occurrence of such self-fertile plants 

 could be interpreted as " mutation," or possibly as a recombination of 

 fixed heredity units which had been separated as a result of previous 

 crossing. However, the various self-fertile plants which first appeared 

 exhibited various gi-ades of compatibility which are suggestive rather 

 that compatibility is a highly variable q-uality. Furthermore, the self- 

 fertilities of the offspring of self-fertile plants in all lines of descent are also 

 of various gi-ades. There is obviously a series of quantitative variations 

 in the behaviour of the plants as wholes that grade from complete self- 

 incompatibility to a very decided self-compatibility. Such a variability 

 of expression of fertilities and such incomplete transmission of the 

 characteristic of self-fertility, as is revealed in all my self-fertilized lines 

 of descent, indicate that occurrence of self- fertility is not due to mutations 

 which are at once fixed, or to recombinations of hereditary units. At 

 least, such recombinations are decidedly not stable. 



Darwin (1SG8, 1877) held that all the facts regarding the occurrence 

 of self-incompatibility then known in such plants as Eschscholtzia 

 californica and Reseda odorata show that the phenomenon is widely 

 distributed and is of decidedly sporadic occurrence. In his opinion, 

 self-sterility is due to " some change in the condition of life acting on 

 the plants themselves or on their parents." The causes were held to be 

 environmental, and the self-incompatibility was assumed to rest in too 

 great a uniformity or similarity of the two kinds of sexual organs pro- 

 duced by a plant. The characteristic of functional fertility, according 

 to Darwin, exhibits fluctuations and chance variation as do other 

 characters. 



Jost's (1907) theory of individual stuffs assumes that the causes of 

 self-sterility (physiological incompatibility) are individual, internal, and 

 epigenetic in that the sex organs fail to function because they are 

 produced on the same plant : the sex organs have the same chemical 

 individual stuff, and thereby lack the differentiation assumed to be 

 necessary for successful fertilization. The causes were fluctuating, but 

 were held to be solely internal. 



Morgan's (1904, 1910) studies of self-incompatibility in the animal 

 Ciona intestinalis, led to much the same conclusion as was reached 

 by Jost. The failures to function are assumed to be due to too 

 great similarity that involves cytoplasmic relations established in the 



