zation (Figs. 32-39). Such varieties are slightly or even not at all 

 fruitful if left to themselves for self-pollination. The pistils, however, 

 are well formed and are capable of forming fruits containing seeds 

 if properly cross-pollinated with good pollen. Since the stamens 

 are more or less impotent these plants are called imperfect herma- 

 phrodites. Such varieties have been called " self -sterile " and the 

 pollen has been spoken of as " impotent " or " lacking in affinity " 

 with pistils. There is, however, very general agreement among 

 those who have investigated the condition of the pollen (Beach 

 1902, Booth 1902, Dorsey 1914, and Detjen 1917) 1 that the sterility 

 is due to the poor condition of the pollen which is thus unable to function 

 at all. 



The so-called " self-sterility " in these varieties of grapes is, there- 

 fore, very different from the " self-sterility " of certain varieties of 

 plums, apples, pears, and cherries, in which the flowers are perfect 

 but the viable pollen is capable of functioning only in certain cross- 

 fertilizations with other varieties or other individuals. In the 

 grape the sterility, it appears, is due solely to imperfect development 

 of stamens and pollen. In the plum the pollen is physiologically 

 incompatible with the female elements of the same plant, of plants 

 of the same clonal variety, and also of certain other plants of diverse 

 origin. In progenies grown from the seed of plants having this type 

 of sterility (Stout 1918. 1920) all degrees of self- and cross-compati- 

 bilities and incompatibilities are often in evidence. 



Studies made of grapes indicate that the imperfections in the 

 stamens very generally, but not always, involve a recurving of 

 filaments which gives a very different flower from that of the perfect 

 hermaphrodite with its erect stamens. 



Among all wild species of American grapes and in seedlings of 

 cultivated sorts another type of flower, the purely staminate, has long 

 been recognized. In this the pistil is much aborted and entirely 

 functionless or is even lacking, but the stamens are well developed 

 and yield much viable pollen. A plant with such flowers is highly 

 fertile as a male parent in cross-pollination but is itself fruitless. 

 It appears that wild species of American grapes consist only of stami- 

 nate plants and imperfect hermaphrodites except perhaps for rather 

 rare cases when individuals are found bearing some or even all 

 perfect flowers. 



1 See Literature Cited, p. 15. 



