The cherries of New York

by U. P. Hedrick

TREE AND FRUIT CHARACTERS OF THE CHERRY

Species of cherries have very characteristic trees. The merest glance at the tree enables one to tell the Sweet Cherry, Prunus avium, from the Sour Cherry, Prunus cerasus. The first named is the larger of the two, especially reaching a greater height, is pyramidal in shape, with branches erect and bearing much less foliage than the Sour Cherry. The Sweet Cherry often lives for a century or more—the Sour Cherry attains but the three score years and ten of man. Prunus cerasus is easily distinguished from Prunus avium by its comparatively low, roundish and never pyramidal head. So, too, many of the varieties of either of these two species are readily told in the orchard by the size or habit of the plant. Other species are either shrubby or tree-like and their varieties may often be identified from the spaciousness or dwarfness of its trees. Size is rather more variable than other gross characters because of the influence of environment—food, moisture, light, isolation, pests and the like—yet size in a plant, or in the parts of a plant, is a very reliable character when proper allowances have been made for environment.

Habit of growth, unlike size, varies but little with changing conditions and thus becomes a most important means of distinguishing species and varieties and not infrequently sets the seal and sign of desirability for an orchard cherry. More than any other character, habit of growth gives what is called "aspect" to a cherry tree. Thus, a species or a variety may be upright, spreading, round-topped, drooping or weeping in habit of growth; the head may be open or dense and may be formed by a central shaft with several whorls of branches or by three or four trunk-like stems each with its scaffolding branches. The trees may grow rapidly or slowly and may be long-lived or short-lived. The trunks may be short and stocky, or long and slender, straight or crooked, gnarled or smooth, these characters often determining whether a cherry is manageable or unmanageable in the orchard.

The degree of hardiness is a very important diagnostic character for groups of cherries and often wholly indicates their value for agriculture. Thus, the varieties of Prunus avium are but little hardier than the peach while those of Prunus cerasus are as hardy or hardier than the apple. The range of varieties as to hardiness falls within that of the species and it is interesting to note that in Europe, where the wild Prunus avium is very common, in the many centuries since the fruit has been under domestication, a cultivated variety hardier than the wild Sweet Cherry has not been developed. Cherries are designated in the technical descriptions as hardy, half-hardy and tender.

Productiveness, age of bearing, and regularity of bearing are distinctive and valuable characters of orchard cherries but not of wild cherries. The care given the tree greatly influences fruitfulness, yet the quantity of fruit produced is often a helpful means of identifying a variety and is a character that must always be considered by the plant-breeder. Age of bearing and regularity of bearing are most important characters with the pome fruits, the apple, in particular, but while worth considering with the drupes are of relatively little value, all drupaceous fruits coming in bearing at about the same time for the species and all bearing regularly, as a rule, unless interfered with by some outside agency preventing the setting or causing the dropping of fruit.

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.

Leaf-buds vary greatly in different species in size, shape, color of the buds and of their outer and inner scales and in the outline of the scales. The angle at which the bud stands out from the branchlet is of some taxonomic value. Vernation, or the disposition of the leaf-blade in the bud, is a fine mark of distinction in separating the cherry from other stone-fruits and while all cherry leaves are supposed to be conduplicate, that is, folded by the midrib so that the two halves are face to face, yet there are slight but important differences in the conduplication of the leaves in both species and varieties. The manner of bearing buds—whether single, in pairs, or in rosettes—must be taken into account, with species at least, and differences in shape and position of leaf and fruit-buds must be noted.

Leaves in their season are very evident and either collectively or individually are valuable determinants of species and varieties. Fruit-growers take little note of leaves, however, though they should be taken into practical account, since their size and number often indicate the degree of vigor. The variability of leaves is usually within limits easily set and occurs most often in young plants, in extremes of soil and climate, and on very succulent growths or water-sprouts. Leaf-size is the most variable character of this organ but is yet dependable in separating several species, as, for example, Prunus avium from Prunus cerasus, the leaves being very much larger in the former than in the latter species. Leaf-forms are very constant in species and varieties, hence especially valuable in classification.

Much care has been taken to illustrate accurately the size and form of cherry leaves in the color-plates in this text but it is impossible to reproduce by color-printing the tints of the leaves, though these are quite constant in both species and varieties.

Other characters of leaves taken into account in describing cherries are thickness, roughness, and pubescence, all of which are somewhat variable, being greatly influenced by climate and soil. Quite too much stress is laid upon the value of pubescence on leaves in determining groups, unless comparisons can be made between plants growing in the same habitat. Possibly more important than any other part of the leaf-blade, in the study of species at least, is the margin. This in the cherry is always serrated and often sub-serrated. These serrations are best studied at the middle of the sides of the leaves, those at the base and apex often being crowded or wanting.

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.

Of all organs, the fruit of the cherry is most responsive to changed conditions and hence most variable, yet the fruits furnish very valuable taxonomic characters in both botany and pomology. In pomology, in particular, the fruits must be closely studied. Size, shape, color, bloom, stem, cavity, apex, suture and skin are the outward characters of which note must be made; while the color, aroma, flavor and texture of the flesh are usually very characteristic. Both species and varieties are well distinguished by the time of ripening though there is much variation in ripening dates. The keeping quality is scarcely taken into account with cherries but varies a great deal, chiefly in accordance with firmness of the flesh. The flesh of cherries, as in all drupaceous fruits, clings to the stone or is wholly or partly free—a character of interest both to the systematist and to the fruit-grower. The color of the juice, whether colorless or red, is a plain and certain dividing line in both species and varieties.

The pits of cherries are rather more lacking in distinction than in other stone-fruits, plums for example, yet they must be accounted of considerable value in determination and for this reason have been included in all of the color-plates of varieties. Cherry-pits from individual trees are almost lacking in differences except in size but between species and varieties show many distinctions not only in size but in shape, surfaces, grooves and ridges, in the ends and more or less in the seeds within. Cherries of any variety grown on poor soils or in incongenial climates tend to have large stones and little flesh, while the pits are smaller and there is more flesh with the opposite extremes in environment. As will be pointed out in the discussion of the group of cherries known as the Dukes, many varieties have pits with shrunken and abortive seeds coming, as we think, from the hybrid origin of these cherries.

The several pages given to the discussion of the characters of cherries are in preparation for a proper understanding of the classifications and descriptions of species and varieties. We are now ready for the classification of the species of cherries which contribute or may contribute forms for cultivation either for their fruits or as stocks upon which to grow edible cherries. The following is a brief conspectus of the edible species of Prunus followed by a fuller conspectus of the sub-genus Cerasus to which cherries belong.