GRAPE BOTANY 303 



most valuable diagnostic characters of species and varieties of 

 grapes. Thus, species differ widely in resistance to phylloxera, 

 the grape-louse, to the grape leaf-hopper, the flea-beetle, 

 berry-moth, root-worm, powdery-mildew, downy-mildew, an- 

 thracnose and other insect and fungous troubles of this fruit. 



The structure of the bark is an important distinguishing 

 character for some species, but is of little importance in 

 identifying the variety and has no economic value to the 

 fruit-grower. In most species of grapes, the bark has distinct 

 lenticels and on the old wood separates in long thin strips 

 and fibers ; but in two species from southeastern North 

 America, the bark bears prominent lenticels and never shreds. 

 Smoothness, color and thickness are other attributes of the 

 bark to be noted. 



Canes of different species vary greatly in total length and 

 in length of internodes. They vary also in size, in number 

 and in color, while the shape in some species is quite distinctive, 

 being in some round, in others angular and in still others flat- 

 tened. The direction of growth in canes, whether sinuous, 

 straight or zigzag, is an important character. Nodes and 

 internodes are indicative characters in some species, being 

 more or less prominent, angular or flattened, while the inter- 

 nodes are long or short. 



The diaphragm distinguishes several species of grapes. The 

 cane contains a large pith and this in most species is in- 

 terrupted by woody tissue, forming a diaphragm at the nodes. 

 In the Rotundifolia grapes the diaphragm is absent, while in 

 several other American species it is very thin and in still 

 others quite thick. The character of the diaphragm is best 

 observed in year-old canes. In studying the (lia])hragm, 

 notice should be taken also of the ])ith, which is very variable 

 in size. 



Young shoots of the graj)e oll'er a ready means of distinguish- 

 ing species and varieties through their color and the amount 



