A. B. Stour 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 differs 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 NV. Forgetiana, N. alata, N. glutinosa, N. auguste- 
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. 
