The peaches of New York

by U. P. Hedrick

TREE- AND FRUIT-CHARACTERS OF THE PEACH

Fruit-growers must largely depend on printed descriptions for knowledge of varieties. A well-made description of tree or fruit, to one mentally equipped to interpret it, is second only to having the real objects at hand. But the difficulty is that few excepting professional pomologists know the characters of even the common fruits and their relative importance. Before taking up either botanical or horticultural descriptions of peaches, then, it is necessary to direct attention to the characters of the peach, differences in which distinguish species and varieties. Be it remembered in this study of the characters of the peach, however, that, as fields and woods offer better facilities for the botanist than the herbarium, so the peach-orchard is a fitter place to study the characters of the peach than a printed page.

The single species of the peach in which we are greatly interested has a very characteristic tree, the variations in which are, however, less well marked than those of the tree of any other of our common fruits. The peach-tree is distinguished by its low, roundish and never pyramidal head. Of its gross characters, size is most important in distinguishing varieties, the several more or less distinct types in the species usually being separable by size alone. In considering size, proper allowance must, of course, always be made for environment. There are no true dwarfs among the varieties of Prunus persica cultivated in America.

Habit of growth is nearly as important as size of tree in determining varieties. Thus, a variety may be round-topped, upright-spreading or drooping in habit; the head may be open or dense; the branches long or short, stout or slender; the trunks may be short or long, straight or crooked, much branched or little branched. These habits of growth serve not only to distinguish sorts but often determine whether the tree is sufficiently manageable to make a good orchard-plant.

Hardiness is an important character both in classifying and in determining the orchard-value of a variety. All peaches are tender to cold as compared with other tree-fruits of temperate climates but there is sufficient difference in varieties to permit the designations hardy, half-hardy and tender. In the classificatory scheme in most common use in America, that of Onderdonk and Price, variation in hardiness is the chief determinant of groups.

All peaches come in bearing so early and bear so regularly that varietal differences in these characters scarcely count in classifying, but productiveness varies very characteristically in different varieties. Environment and care greatly influence fruitfulness yet, notwithstanding, the quantity of fruit borne is often a means of identifying a variety and, of course, must always be considered by the cultivator and the breeder.

Resistance to disease and insects is a taxonomic and an economic character of much importance. Thus there are great variations among varieties in resistance to peach-yellows, brown-rot and leaf-curl, the three commonest diseases of this fruit in New York, as there is also in resistance to San Jose scale, the worst insect-pest of the peach in this region and to the peach-borer, the commonest. These examples are multiplied in the discussions of varieties, pains having been taken in the peach-orchards at this Station to determine the relative resistance of all varieties to the pests of this region.

But little attention need be paid to the old bark on peach-trees, since in all varieties it is much the same and is unimportant to the cultivator. The bark of all varieties varies in color on different soils and is always of a lighter hue in cold than in warm regions, in dry than in wet situations.

The branches and branchlets of varieties are very characteristic. The length, thickness, direction, rigidity and the branching angle are all stable characters of varieties, changing but little with differences in soil and climate. The length of the internode is important as is also color, smoothness, amount of pubescence, size and appearance of the lenticels, and the presence of excrescences,—though all are exceedingly variable.

Both leaf-buds and fruit-buds are used in separating groups of peaches but are too nearly alike in the several groups to be of aid in distinguishing the varieties of any group. Fruit-buds are borne in pairs on the wood of the previous year with a leaf-bud separating the members of the pair. The only characters of buds worth noting are size, shape, color and the angle at which the buds stand out from the branches.

After the fruits, the leaves offer the best means of determining groups and varieties of peaches. Leaves are variable, it is true, but usually within limits quite easily set, since the conditions causing the variations are easily discovered. The most usual ones are extremes in soil, moisture, light, heat and the age of the wood upon which the leaves are borne. Much care has been taken to illustrate as accurately as possible the leaves of the varieties given color-plates in this text, size and form being reproduced exactly and color as nearly as color-plate printing permits.

Leaf-size and leaf-form are the first characters of the foliage to study in determining varieties. The former varies somewhat in accordance with the conditions named in the foregoing paragraph but the shape of the leaf changes but little. Fortunately for the student of varieties, leaves differ most in relative length and breadth so that the shape may be accurately indicated by figures which are used in most of the descriptions in The Peaches of New York. Comparisons of the bases and the apices of leaves of different varieties often show distinguishing marks.

The color of leaves in varieties is very constant for both surfaces. The color of the foliage gives an aspect to peaches whereby a variety may often be distinguished in its summer dress at considerable distance. Unfortunately, the colors of leaves in the color-plates in this book cannot be relied upon to give much help in studying this character. Autumnal tints are uniformly the same in peaches and not to be relied upon in classifying varieties.

Several other characters of the leaves must be studied by the systematic pomologist. The leaves of some varieties are thinner than those of others, hence thickness becomes a distinguishing character. Venation of leaves—size and arrangement of veins—is important. Pubescence of leaves cuts quite a figure in the descriptions of many fruits but in the peach is of minor importance because the leaves are not very hairy and the quantity and character of the pubescence is exceedingly variable. Some varieties have relatively few leaves—others many. The leaves of some varieties fall early—others relatively late.

The margins of peach-leaves offer valuable evidence in determining varieties. They may be serrate or crenate, doubly or singly divided, glandular or glandless. Both serrations and glands are best studied in the middle of the sides of leaves, those at the base or apex often being crowded or wanting.

Petioles differ in length, thickness, rigidity, pubescence and color, so that this organ is often a substantial help in identifying varieties. Some say the color of the petiole is correlated with that of the fruit, as it certainly is in such extreme sorts as Snowball and Indian Cling, but it is doubtful whether this correlation goes further than groups and even here does not always hold. Stipules offer no distinguishing marks of importance.

Much use is made in classifying peaches of the presence or absence, the size, color, shape, position and number of glands on the base of the leaf or on the leaf-stalk. These glands may be either stalked or sessile. The terms used in describing glands are easily understood and need no definition unless it be a few words in regard to the shape. Globose glands are small globes, reniform glands are kidney-shaped. In determining the form of glands examinations must be made several times in the season, the end of the summer offering the best opportunity and even then care must be taken to secure old leaves. Glands are less variable in adult trees than in trees not yet in bearing. Pomologists for a hundred years have noted the fact that peaches with glandless leaves are very susceptible to mildew. We find this to be the case on the grounds of this Station. This correlation between glandlessness and mildew may account for the fact that peaches with glandless leaves are rapidly disappearing from American peach-lists. Wickson says it has been found that peaches with glandless leaves resist leaf-curl.[163]

Gregory has made a careful study of the glands on peach-leaves.[164] We publish here the most important facts he brings out.

"In a large number of cases the glands are stable and can be safely used to aid in the identification of certain varieties. There are also varieties in which the glands are exceptionally unstable, being on the border line between the two types—reniform and globose—and having what might be termed mixed glands. These mixed glands are of two kinds: one in which the majority of the glands are reniform, with some globose intermingled; the other in which the globose form predominates. It would be quite possible, as Carriere (1867) suggests, to distinguish a third type of glands—the mixed type.

It is important that leaves should be chosen from healthy branches on bearing trees. It is also best to obtain a large number of leaves or to examine the tree carefully before making the final selection of leaves. Mature leaves are best because their glands are full-sized and correctly shaped, while on young leaves the form of the glands is usually obscure. This is particularly true of the reniform glands. On the other hand, old, partly decayed, globose glands frequently have much the appearance of reniform glands.

The structure of the glands shows that they are true glands, having an upper layer of long, rectangular, secretory cells that produce a sweet substance, the function of which is not apparent. After the glands have ceased secreting they begin to decay, becoming brown on the upper surface and slowly disappearing until almost nothing is left. This decaying is a very complicated process, being preceded in every case by a suberization and thickening of the cell walls.

"The spines of the leaf are very similar to the glands in structure, having the same upper layer of long cells, but with much more heavily cutinized walls. A study of the transitional forms indicates that the glands are merely modified leaf spines.

The leaves with reniform glands are apparently the highest type and the glandless leaves the lowest, with the transition through the globose type. In support of this view is the fact that whenever typically glandless leaves become possessed of glands they are always of the globose type.

The serrations of the glandless leaves are very strikingly different from those on a leaf with glands. The former leaves are deeply and doubly serrate, while the margins of the latter are always single and crenate. Almost invariably, when glands develop on a normally glandless leaf, the serrations are transformed to crenations, indicating that there is a very close correlation between the glands and the crenations on the edges of the leaves."

The French pomologists, Poiteau and Turpin,[165] seem to have first made note of the glands in describing peaches, recording their discovery by M. Desprez in the nurseries at the Luxembourg in 1810, after which, for a half-century, French, English and German pomologists regarded them as an infallible means of distinguishing varieties. But, by the middle of the Nineteenth Century, classifiers began to give them up because of their variability on leaves of trees of the same variety or even on the same tree. Even Darwin made note of their insufficiency in taxonomic work.[166] Now, no one familiar with any considerable number of varieties of peaches would attach very great importance to glands in a system of classification.

The flowers of peaches are very characteristic, helping to delineate the groups in the several classificatory schemes of various pomologists and being ample to identify not a few varieties. Peach-flowers differ in time of appearance; in length of blooming-season; they may be large, medium or small; pink, rose and rarely white; borne on pedicels of varying length, thickness, color and pubescence; and both the floral and reproductive organs have modifications of their several structures. The size, color and shape of peach-flowers are well shown in the first six color-plates. In some species of Prunus, as some of the plums, the reproductive organs differ greatly in ability to perform their functions, but the blossoms of edible peaches are seemingly always self-fertile and there are less often the mal-formations found in the reproductive organs of some plums.

A well-marked correlation[167] between the color in the inside of the calyx-cup and the color of the flesh of the fruit is one of the distinguishing features of peaches. Yellow-fleshed peaches develop from blossoms in which the inside color of the calyx-cup is orange; white-fleshed peaches develop from those in which the color is greenish or greenish-yellow sometimes approaching a very light orange easily distinguished from the dark orange of the other group. Since the discovery of this correlation in the Station orchards by Mr. Charles Tubergen it has been in yearly use and has enabled us to tell a year or two in advance the flesh-color of seedling peaches, since the first peach-blossoms seldom set fruit.

The fruits, however, furnish by far the best characters upon which to found a classification of peaches. The simplest classification of peaches begins by separating them into smooth-skinned and pubescent sorts; each of these divisions is redivided into clingstones and freestones; these four groups may then be separated into yellow-fleshed, white-fleshed and red-fleshed peaches; still further, most, not all, of the twelve groups made in the first three divisions, separate into round, flat or beaked peaches. These are the major characters of the fruits, little influenced by cultivation or environment, after which there are many minor characters such as size, shape, color, quality and season, all very responsive to changed conditions, that help to describe definitely the many varieties of Prunus persica. The most variable of the minor characters is shape, all peaches tending to lose rotundity in southern climates and to become oblong and beaked. The length and quantity of the pubescence on peaches vary considerably in different soils—the warmer and lighter the soil, the less pubescence. The skin adheres closely to the flesh in some varieties; in others it is non-adherent.

The characters found in the stones of the many species of Prunus are of great value in determining species but they help but little in determining the horticultural varieties of any one species. The stones of the peach do vary, however, very materially in size, shape, grooves and ridges, pitting and in characteristics at base and apex. The color-plates in this text illustrate these differences very well. One may generalize and say that the stones of the freestones are more deeply furrowed and that the sides are smoother than in the clingstones.

The characters of the peach are set forth on the opposite page by reproducing a description as made at this Station in describing a variety for The Peaches of New York. Such a description is, however, but a skeleton, as dead as dry bones, unless a living picture of the variety be made by filling out and covering the skeleton with ample remarks made as the describer studies the plant in the field.

A more detailed discussion of the horticultural and botanical characters of the peach logically follows here.