LEAVES 35 



The angle which the petiole forms with the twig has long been 

 recognized as a means of identifying apples, and Shaw has re- 

 cently discovered that this character is correlated in all varieties 

 with the form of the top.^ Varieties in which the angle is sharp 

 have an upright head; those in which the angle is broad, a 

 spreading head. Thus the form of the top can be foretold while 

 the tree is in the nursery. 



56. Leaf appearance and fall. — There are no true evergreens 

 among the hardy fruits, although the strawberry and a few 

 blackberries and dewberries bear leaves which have two growing 

 seasons. There are considerable differences in related species 

 and varieties as to the time the leaves push from the buds in the 

 spring and drop from the stems in the autumn. In plums, cur- 

 rants, grapes, and gooseberries, leaf appearance and fall are 

 characters of first magnitude in distinguishing species. The 

 fall of leaves is worth noting only as a natural process and 

 counts for nothing when leaves are killed by freezing, disease 

 or other outside agencies. 



In mild climates, as in the American South and far West, 

 the differences in leaf appearance and fall are much greater 

 than in colder regions where winter bursts suddenly into spring 

 and autumn into winter. Indeed, in mild climates the prepara- 

 tion for leaf fall, a process of ripening, is so imperfect that the 

 leaves are wrenched off by winter storms or pushed off in the 

 spring by the growing buds beneath them. 



Leafing time and leaf fall help greatly in classifying currants, 

 a fruit in which there is much confusion both as to species and 

 varieties. Thus, one group of varieties, of which Wilder is 

 representative, puts out its leaves very early; another group, 

 best represented by Prince Albert, holds the foliage very late 

 in the autumn. 



57. Color of leaves. — The color of leaves is very constant in 

 species and varieties, either when studied in individuals or taken 

 in mass. Species and varieties are given a distinct aspect by 

 their summer dress, which is chiefly dependent on the color of 

 the leaves, but may be changed greatly by the size and number 

 of leaves. The color of the upper and lower surfaces of leaves 



1 Shaw, J. K. Leaf Characters of Apple Varieties. Bull. 208 : Mass. Agr. 

 Exp. Sta. 1922. 



