The degree of hardiness is a very important diagnostic character in determining both species and varieties of grapes and very largely indicates their value for the vineyard. Thus, the varieties of the European grape are less hardy than the peach, while our American Labruscas and Vulpinas are as hardy as the apple. The range of varieties as to hardiness falls within that of the species, and cultivated varieties hardier than the wild grape are not found. Grapes are designated in descriptions of varieties and species as hardy, half-hardy and tender.
Habit of growth varies but little with changing conditions and is thus an important means of distinguishing species and varieties and not infrequently stamps the variety as fit or unfit for the vineyard. Habit of growth gives aspect to the vine. Thus, a vine may be upright, drooping, horizontal, stocky, straggling, spreading, dense or open. The vine may grow rapidly or slowly and may be long-lived or short-lived; the trunk may be short and stocky or long and slender. These several characters largely determine whether a vine is manageable in the vineyard. Productiveness, age of bearing and regularity of bearing are distinctive characters with cultivated grapes. The care given the vine influences these characters; yet all are helpful in identifying species and varieties and all must be considered by the grape-grower.
Immunity and susceptibility to diseases and insects are 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, anthracnose 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 flattened. 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 internodes are long or short.
The diaphragm distinguishes several species of grapes. The cane contains a large pith and this in most species is interrupted 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 diaphragm, notice should be taken also of the pith, which is very variable in size.
Young shoots of the grape offer a ready means of distinguishing species and varieties through their color and the amount and character of the pubescence. Shoots may be glabrous, pubescent or hairy and even spiny.
The tendril is one of the organs most used in determining species and varieties of grapes. In some species, as V. Labrusca, there is a tendril or an inflorescence opposite nearly every leaf, continuous tendrils. All other species have two leaves with a tendril opposite each and a third leaf without a tendril, intermittent tendrils. To study this organ it is necessary to have vigorous, healthy, typical canes. Tendrils may be long or short, stout or slender; simple, bifurcated or trifurcated; or smooth, pubescent or warty.
The number of inflorescences borne by species is an important character in some cases. All species, excepting V. Labrusca, average two inflorescences to a cane, but V. Labrusca may bear from three to six inflorescences, each in the place of a tendril opposite the leaf.