498 BOTANY OF CROP PLANTS 



and pistillate." He finds all gradations between "pseudo- 

 staminate" and "pseudo-pistillate" forms among wild 

 species. 



Grape Pollen .^ — In a study of grape pollen, Booth found 

 that self-sterile pollen differs from self-fertile pollen. In the 

 self-fertile form, the grain is surrounded by a mucilaginous 

 substance which causes them to stick together; the grain is 

 oblong in shape, symmetrical, and blunt at the ends. Self- 

 sterile pollen has no mucilaginous substance about it; it is 

 irregular in shape and more pointed at the ends. Self- 

 fertile and self-fertile pollen may be mixed in the same 

 variety. The degree of self-sterility or self-fertility seems 

 to vary with environmental conditions. 



"Couloure" of Muscat Grape. — This valuable raisin grape 

 has a tendency to drop its blossoms without setting fruit. 

 This trouble is known as "couloure." It results from a lack 

 of fertiHzation. This is due to the fact that in this variety 

 stamens are shorter than the pistil, that the pollen has a 

 tendency to stick together in masses which makes its dis- 

 tribution less certain, and to the rather frequent development 

 of imperfect pollen grains. The difficulty is largely overcome 

 by planting, in the Muscat vineyard, varieties that produce 

 an abundance of viable pollen, and that blossom at the same 

 time as the Muscat. These varieties will furnish pollen for 

 fertilization of Muscat flowers. 



Flowers in Wild Grapes. — Grapes in the native condition 

 differ from those in cultivation. The wild forms seldom bear 

 self-fertile perfect flowers. In these, there are just two sorts 

 of vines: (i) staminate, and (2) self-sterile hermaphrodite. 

 There are no self-fertile hermaphrodites. The staminate 

 flowers have abortive pistils, and the so-called pistillate forms 

 retain their stamens, but they are abortive. 



