The petiole may be used to good advantage in distinguishing both species and varieties. Thus, in consequence of the great length and slenderness of the petiole of leaves of Sweet Cherries, the leaves are always more or less drooping, while those of the Sour Cherry are usually erect by reason of the petiole being short and strong. The color of the petiole is said by some to be correlated with that of the fruit--a statement that needs verification. The pubescence of the petiole must be noted.
The position, size, shape and color of the glands on cherry leaves must be noted as they are fairly constant guides. They are usually on the petiole at the base of the leaf but are sometimes on the leaf itself. The glands are commonly given as globular or reniform in shape but there are often intermediate forms the shape of which is hard to classify.
Stipules in this plant have considerable taxonomic value, having some distinguishing marks not possessed by the leaves. Cherry leaves springing from dormant leaf-buds have very small stipules, sometimes so minute as hardly to be seen, but on the current year's growth the stipules are larger, being largest at the tip of the branchlet. There is considerable difference in the size of these organs in varieties of the same species. Stipules of the cherry are nearly always borne in pairs. The small stipules, appearing with the first leaves, drop, at this Station, about the middle of June while those accompanying the later leaves on the wood growth of the current year remain until in July, there being a difference in varieties as to how long they remain. All stipules are deeply toothed and bear glands of varying color and shape on the serrations, the characters of both serrations and glands offering some distinguishing marks for species and varieties.
The flowers of cherries are very characteristic, as a study of the color-plates of blossoms will show, furnishing a wholly distinctive mark of species and helping to distinguish varieties. The flowers are hermaphrodites and are borne in more or less dense, corymbose clusters. Individual flowers in species and varieties vary in size, shape, color and odor. The peduncles are long or short, as the case may be; the corolla furnishes distinctions in size, shape and color of petals; the calyces are chiefly distinguished by their glands and the amount and character of the pubescence; while stamens and pistils offer differences in size, color of their different parts and in the number of stamens. In plums the reproductive organs differ greatly in ability to perform their functions, some varieties being self-sterile. In New York there seem to be no marked differences in fecundity in cherries nor are there so frequently the malformations of reproductive organs which are found in plums. The season of flowering is a fine mark of distinction between species and varieties, a fact well brought out by the chart on pages 80-81.