VITACE^ 497 



there is an equal number of nectar glands between. The 

 one pistil is two-celled and two-ovuled. The fruit is a 

 berry. 



Dorsey has cited marked variations in the flowers of the 

 genus Vitis: stamens may vary from three to nine; petals, 

 nectariferous glands, and carpels have a corresponding 

 numerical variation. 



Opening of Flower and Pollination. — Flower Opening. — 

 The opening of the grape flower is indicated by the breaking 

 away of the petals at the base (Fig. 2 10). In some instances, 

 all the petals break away at about the same time; at other 

 times, one petal may initiate the. process, and be followed 

 by the others. The cap of five petals, adhering at their 

 apices, finally falls off. The rate of flower opening varies 

 from a few minutes to several hours. The anthers seldom 

 open until the cap falls off. Most grapes are insect pollinated. 



Self -sterility. — Many cultivated varieties of grapes are 

 self-sterile; this is due, for the most part, to impotent pollen. 

 Some cultivated varieties are perfectly self-fertile, others 

 partially self-fertile, and still others entirely self-sterile. 

 As has been indicated, perfect flowers bearing reflexed 

 stamens usually have impotent pollen. However, in some 

 cases, perfect flowers with erect stamens also bear impotent 

 pollen. As a rule, the self-fertile varieties, those that can 

 develop marketable clusters when self -fertilized, have long 

 stamens. Self-sterile varieties, those that cannot produce 

 marketable clusters of fruit when self-fertilized, usually 

 possess short stamens. However, long stamens and short 

 stamens are not absolute criteria of self-fertility and self- 

 sterility respectively. With but few exceptions, the strongly 

 self-sterile varieties are hybrids. Booth suggests that the 

 grape is "now in a'state of evolution from an assumed older 

 hermaphrodite form to forms which are essentially staminate 

 32 



