A. B. Stout 91 



usually contain well developed seeds ; there is close correlation between 

 fruitfulness and seed production, as perhaps is the rule in the great 

 majority of seed plants. In the apple she finds that seedless fruits are 

 frequent and that in some varieties seedlessness does not involve any 

 decrease in the size of the fruit. In some varieties, however, there 

 appears to be a decided inter-relation between fruit-development and 

 seed-development as Ewert (1909) and Kraus (1915) have particularly 

 pointed out. The relation between the conditions which lead to par- 

 thenocarpy and those which lead to bulbil formation for example is by 

 no means clear. Evidently there are various types of parthenocarpy ; 

 in some cases it is apparently a purely vegetative phenomenon, in other 

 cases pollination seems necessary for its initiation. 



The conditions in the fruit-sterile (to self-pollination) and the seed- 

 sterile (seedless) varieties of apple also raise some question as to the 

 stage at which fertilization fails in these cases. Kraus is of the opinion 

 that in self-sterile varieties generally the union of the proper nuclei 

 within the embryo sac is apparently normal (Kraus, 1915, p. 554). If 

 this be true then the incompatibilities come to their expression after 

 fertilization, perhaps as embryo abortion. Ewert (1909) however holds 

 that the more or less rudimentary seeds in the so-called seedless, and in 

 the feebly self- fertile varieties, are largely, if not entirely, due to partheno- 

 genesis. Sutton states that " the stage at which fertilization fails 

 probably differe in various forms." 



Recent papers by East and Park (1917), and by East (1918), extend 

 considerably our knowledge of self- and cross-incompatibilities in certain 

 species of Nicotiana and their hybrids, and decidedly modify previous 

 statements of fact and theory for these species. 



It now appears that N. Forgetiana, N. alata, N. glutinosa, N. augusti- 

 folia, and various of their hybrid offspring may be self-compatible to 

 some degree and that cross-incompatibility may also be strongly in 

 evidence. The variability of the relations, both self and cross, is hence 

 much greater than was previously reported by East (1915), and in this 

 general condition these species of Nicotiana are apparently not funda- 

 mentally different from other self-incompatible species. 



East and Park also present very interesting evidence that sex 

 compatibilities may show cyclic changes, becoming stronger with the 

 full maturity of plants. They find a decided tendency for incompati- 

 bility, both self and cross, to appear during the period of vigorous bloom, 

 and then to disappear near the end of the blooming period. 



