90 Self-hicomiKitibility in Hermaplirodite Plants 



different results if reciprocal matings were made at different times 

 during the period of bloom. 



These cases of difference in the compatibility of reciprocal matings 

 point very clearly to a source of fluctuating variability by no means 

 sufficiently recognized, and that is the complexity of the fertilization 

 processes as revealed by cytological study. It may well make a difference 

 which parent furnishes the male and which the female when we realize 

 the possibility of variation offered in the complex processes of cyto- 

 plasmic fusion, nuclear fusion, pairing of homologous chromosomes and 

 the arrangement of the pairs with reference to each other, to the nucleus, 

 and to the cell as a whole. 



Sirks recognizes that the conditions in F. phoeniceum indicate that 

 " auto-incompatibilite " is a phenomenon of physiological sex differentia- 

 tion which cannot be ascribed to fixed genotypic constitution nor to the 

 inheritance of specific line stuffs. He suggests that the poor growth of 

 pollen tubes very generally observed in cases of incompatibility may 

 involve osmotropism. 



Evidence that self-sterility is somewhat exclusive of, and more 

 specific than, cross-sterility is given by Sutton (1918). The evidence 

 of a wide range of variation in self-compatibility among the various 

 cultivated (propagated asexually) varieties of plum, of cherry and of 

 apple has been confirmed by studies of varieties commonly grown in 

 England. Self-fertile, partially self-fertile and self-sterile varieties are 

 reported in each of these quite as have been found by other investigators. 

 Sutton finds, however, no evidence of cross-incompatibility between 

 varieties except in crosses between the Jefferson variety and the Coe 

 group of varieties of plums. She concludes that otherwise inter-varietal 

 cross fertility under field conditions depends solely on the production of 

 plenty of pollen and on simultaneous blooming. The varieties of the 

 cherry reported cross-incompatible by Gardner (1913) were not studied 

 by Sutton. 



Sutton's data show clearly that a distinction is to be made between 

 fruitfulness involving only parthenocarpy, and fruitfulness with and 

 dependent upon seed reproduction. In the case of the navel orange the 

 size and quality of the carpels are quite independent of any process of 

 fertilization, or even of parthenogenetic production of seed ; the pistils 

 however contain normal ovules, and when pollination occurs fertilization 

 results and seeds are formed even in the accessory carpels (Shamel, 

 1918). Sutton finds in plums and cherries that well formed fruits 



