DorRSEY: VARIATION IN FLORAL STRUCTURES OF VITIS 39 
Flowers possessing no stamens do not occur, or at least have not 
been recorded. Among these existent floral types which way is 
the evolution taking place? Goebel (’98) states ‘as a further 
peculiarity of the angiospermous flower that it is predominantly 
hermaphrodite, and unisexual flowers can be proved to be fre- 
quently the result of arrest of either the microsporophylls or the 
megasporophylls.”’ 
The perfect form of flower occurs in the cultivated varieties of 
many species of grape. In fact, this form of flower, according to 
Engelmann, has, by some, been considered of taxonomic value in 
V. vinifera. As has been noted, however, in wild vines of V. bi- 
color and V. vulpina the perfect flower with upright stamens was 
not observed in 347 individuals. Nevertheless, Beach (’98 and 
’99) and Booth (’02) have shown that in many cultivated forms 
with perfect flowers, having reflexed stamens, the pollen is abortive 
to a variable extent, this often rendering the flower pistillate,— 
at least functionally. Under similar conditions, also, vines are 
found bearing flowers with partially developed stigmas; and func- 
tionally these may be considered on the border line between the 
perfect and staminate forms. (PLATE 1, FIG. 9.) 
Even taking into consideration these variations, there were 
observed to occur among the wild vines native to the region about 
Ithaca and Geneva, N. Y., only the staminate form and the perfect 
form with reflexed stamens. This would seem to indicate that 
the evolution is toward the dioecious habit. 
In the genera closely related to Vitis there is a similar condition 
with respect to differentiation. According to Small, Cissus L. 
is perfect or sometimes polygamous, Ampelopsis Michx. mostly 
perfect, and Parthenocissus Planch. perfect or polygamo-monoe- 
cious. In this regard the degree of differentiation in Vitis and in 
the genera related to it is therefore considerable. These varia- 
tions are both structural and functional. It is not clear which is 
the most primitive form, so that attempts to determine precisely 
the direction toward which evolutionary changes are now taking 
place would be largely speculation. 
THE FLOWER CLUSTER: The branching habit of the grape is 
sympodial. The tendrils, or early in the growth of the shoot, the 
clusters, are the terminal growths of the stem. Upon further 
