THE PLUMS OF NEW YORK. 7 



of consideration though quite too much has been made of these char- 

 acters, especially of pubescence, in determining species, for they are all 

 extremely variable. 



The size, shape and color of leaf -buds and of their outer and inner 

 scales and the margins of the scales differ in different species. Possibly 

 the most evident, and therefore readiest means of identifying species, at 

 least, is by the leaves. It is true that leaves are very variable but always 

 within limits, and either individually or collectively in giving the general 

 aspect to a tree they are characteristic. Modifications of leaves most often 

 occur in very young plants, those growing in bright sunshine or deep shade 

 and on sprouts or suckers, but none of these are usually sufficient to mis- 

 lead as to species. Leaf-size and leaf-form are the first characters to be 

 noted in determining a plum but these are closely followed in value by 

 leaf -color, leaf -surface, leaf -thickness and leaf -margin. Leaf -size is variable, 

 depending much upon the conditions noted above but leaf -form varies but 

 little in the several species. So, too, the color of leaves is very constant 

 throughout a species, for both surfaces, though impossible to describe accu- 

 rately in words and very difficult to reproduce in color-printing. There 

 is a marked difference in autumnal tints not only of species but of varieties 

 but these are not very constant in any one location and must vary greatly 

 under different environments. The thickness of the leaves of the several 

 species is a distinctive character. Species of plums have very different 

 leaf-surfaces as regards reticulation, rugoseness, pubescence and coriaceous- 

 ness, all of these characters being quite constant, though it is to be noted 

 that roughness of leaves and pubescence are increased by exposure to the 

 sun and by the influence of some soils. There is, indeed, considerable 

 variation in the pubescence of the leaves of all species of plums in different 

 parts of the country and probably too much has been made of pubescence 

 as a determining character. 



The margins of leaves are very characteristic of species and scarcely 

 vary under normal conditions if the teeth at the middle of the sides be taken 

 rather than those toward the base or apex, these very often being crowded, 

 reduced or wanting. The presence of glands, their position, size, shape 

 and color, help to characterize several species and seem to be fairly con- 

 stant guides. Some species and a great number of varieties have the 

 distinguishing marks of gland-like prickles tipping the serrations in the 

 leaf-margins. Length, thickness, rigidity and pubescence of petiole have 

 some taxonomic value. Stipules usually offer no distinguishing marks 

 other than those mentioned under leaves. 



