Immunity and susceptibility to diseases and insects are valuable taxonomic characters of both species and varieties of cultivated cherries. Thus, the varieties of _Prunus cerasus_ are very susceptible to black knot (_Plowrightia morbosa_), while those of _Prunus avium_ are almost immune. On the other hand, _Prunus avium_ is an inviting prey to San José scale (_Aspidiotus perniciosus_), while _Prunus cerasus_ is but little injured, indeed, seldom attacked; _Prunus mahaleb_ appears to be almost wholly immune to the powdery mildew (_Podosphaera oxyacanthae_), while _Prunus avium_ and _Prunus cerasus_ are much attacked, though Wood, a variety of _Prunus avium_, is almost immune. The English Morello, a variety of _Prunus cerasus_, is very subject to leaf spot (_Cylindrosporium padi_), while Montmorency, of the same species, is nearly immune. These examples can be multiplied many times by references to the discussions of varieties, and represent only observations on the grounds and in the neighborhood of this Station. They serve to show the great importance, to the fruit-grower, the plant-breeder and the systematist, of natural resistance to disease and insects. Both the outer and the inner bark have considerable value in determining species but are of little importance in identifying varieties and have no economic value to the fruit-grower and hence but little to the breeder. Smoothness, color, thickness and manner of exfoliation are the attributes of the outer bark to be noted, while the color of the inner bark is the only determinant and that relatively unimportant. In young trees the bark of the cherry of all species is smooth, glossy or even brilliant; but later it becomes uneven, scaly and dull, usually ash-gray but varying in all of these characters to an extent well worth noting for taxonomic purposes. Cherries, in common with most trees, have a lighter colored bark in cold than in warm regions, and in dry than in wet areas. Branches and branchlets are very characteristic in both species and varieties. The length, thickness, direction, rigidity and the branching angle are valuable determining characters and very stable ones, changing but little even with marked variations of soil and climate. Thus, a Sweet Cherry tree can be told from a tree of the Sour Cherry, or the English Morello can be distinguished from Montmorency by branch characters as far as the outlines of the trees are discernible. Few cherries bear spines but all are more or less spurred and these spurs are quite characteristic even in varieties. With the branchlets the length of the internodes should be considered and their direction, whether straight or zigzag; also color, smoothness, amount of pubescence, size and appearance of the lenticels, the presence of excrescences, are all to be noted in careful study though all are more or less variable, pubescence especially so, this character being too often relied upon in descriptions by European botanists and pomologists.