THE CHERRIES OF NEW YORK II 



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 Jos6 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 Mont- 

 morency, 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 deter- 

 mining 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 Hghter 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 intemodes 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 



