Chapter II: Botanical and Horticultural Classifications of the Peach (1)

PLACE OF THE PEACH IN THE GENUS PRUNUS

The genus Prunus is without peer in the number of distinct, natural, esculent products it furnishes man. Here belong the stone-fruits--peaches, plums, cherries, almonds and apricots, represented by some forty edible species, which, through long domestication, have been broken up into not less than 5000 orchard-varieties, of which at least 3000 are now under cultivation. Of the two-score cultivated species of this genus, _Prunus persica_, the common peach, is easily the most remarkable when judged either by the senses which make foods palatable and pleasant or by the criteria that establish the commercial worth of a product. As virtues which give the peach leading place among stone-fruits, we may specify: Wider distribution and consequently commoner cultivation and a greater number of varieties; larger size, greater beauty, pleasanter and more diversified taste, and more culinary uses than other stone-fruits; and greater productiveness, more rapid growth and earlier fruiting of the trees than most of the species of the genus. The place of the peach in the genus Prunus is thus easily established from a horticultural point of view, but it is a much more difficult matter to make clear its botanical standing among the species with which it is considered botanically related.

The botanical relations of the several stone-fruits to each other have been set forth in the foregoing books of this series on plums and cherries, but, for the convenience of those who may not have these treatises, a summary of the relationships of the species of Prunus is presented. Besides, greater emphasis on several differences between the peach and its congeners is needed. In particular, since some notable naturalists have held that the peach is a modified almond, the differences between these two fruits must be more clearly set forth.

Nearly every botanist who has done much towards classifying plants has grouped the stone-fruits according to a plan of his own and there are, therefore, many classification schemes and consequently a most confused nomenclature for this genus. Happily, the pitfalls in synonomy dug by botanists need not worry horticulturists; for each of the stone-fruits constitutes a distinct horticultural group. In tree or fruit of peach, plum, cherry, apricot, or almond, who could mistake one for another? For horticultural purposes we accept as best one of the oldest and yet one of the most commonly used classifications which places in one genus all of the stone-fruits. What are the lines of cleavage between the several stone-fruits of common cultivation?

Stone-fruits fall naturally into two distinct groups. In the first the leaves are rolled in the buds--convolute. The plums and the apricots belong to this section. In the buds of the other group the leaves are folded lengthwise along the midrib--conduplicate. To this section belong almonds, peaches and cherries. The two sections seem to be united in this matter of disposition of leaves in the bud, it should be said in passing, by a few species of American plums which are conduplicate in vernation. The second section is further subdivided by very marked differences in the fruits. The fruits of the peach and almond are larger than those of the cherry, less juicy,--in the case of the almond almost dry,--hirsute (except in the nectarine), and are borne without stems; and the blossoms usually appear long before the opening of the leaves. Cherry-fruits are always juicy, usually glabrous, and are borne on more or less distinct stems; and the blossoms appear with the leaves. Botanists who put these fruits in one genus usually redivide according to the characters given so that the plum and apricot stand in one sub-genus (Euprunus), the almond and peach in another (Amygdalus), and the cherry in a third (Cerasus).

Differentiating more closely, we find that it is not so easy to distinguish between the peach and the almond. The likenesses are so many and so apparent that it is not to be wondered that Knight, whose theory we have discussed on a foregoing page, came to the conclusion that the peach is a modified almond, or that Darwin, with his belief that plants came sooner or later to express their environmental conditions, should be inclined to believe that the peach is an evolution from the almond. It is easy to imagine that countless ages ago--how long since is but an invitation to argue--the two species merged into one. Offspring of the parent-species once established in distinct soil and climatic conditions--the peach in China, the almond in southwestern Asia--differentiation began and in time each region was represented by a species of its own. Such an occurrence is but one of the commonplaces of evolution; but Knight, Lindley and Darwin thought they saw evidence that the separation came after the almond, the supposed parent-species, had been domesticated, the steps being from fleshy almond to bad clingstone, to good clingstone, to freestone, to nectarine. The arguments against such a descent have been given elsewhere.

The chief differences between the two species are to be found in the matured fruits though, at first thought, it might appear that these are not greater than those found in widely separated varieties of either of the two species. The fruits of the peach and the almond are, however, much more widely separated than any of the varieties of either species, inasmuch as the differences are several and have to do with parts not usually affected by cultivation and not the subject of selection by the cultivator. Thus, the fruit of the peach is a delectable esculent; that of the almond inedible; the flesh of the peach, the mesocarp, is soft, fleshy, juicy; that of the almond thin, tough and leathery; the pit of the peach must be removed while that of the almond drops naturally from the hard flesh which splits at maturity. The differences between the pits of the two species are quite as marked as in the flesh of the fruit. The pit of the peach is deeply sculptured, pitted, and of a bone-like consistency; that of the almond is nearly smooth and in most varieties is much thinner and of softer texture. The differences in the kernels are such as could easily be brought about by selection, some peach-kernels being sweet and edible and some almond-kernels being too bitter to be palatable.

Coming to the tree-characters we find that there are several which differ sufficiently to give each of the two fruits distinct specific rank. The winter aspect of the two trees is wholly different. The almond resembles a young apple tree in color of bark more than it does the peach and has, too, a head much like that of a broad-topped, much-branched apple. In foliage the distant aspect is much the same, but examined closely there are several distinctions that hold in comparing the two species. The leaves of the peach are more broadly lanceolate than those of the almond, coarsely serrate or crenate while the margins of almond-leaves are finely serrate. The glands on the leaf-stalk or leaf of the peach are globose, reniform or mixed; on the almond, the glands are globose. The flowers in the two species are similar but the time of flowering is markedly different. The color of the petals in both varies from pale pink to deep pink with occasional pure white forms; the flowers of true almonds are always large while those of the peach are about equally divided between large and small. The almond, in New York, is out of bloom before flowers of the peach appear, the difference in blooming-time being from one to three weeks.

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.

PRUNUS PERSICA Stokes.

1. _P. Persica_ Stokes _Bot. Mat. Med._ =3=:100. 1812.
2. _P. Persica_ var. _vulgaris_ Maximowicz _Mel. Biol._ =11=:668.
1883.
3. _P. Persica_ var. _necturina_ Maximowicz l. c. 669. (nectarine)
4. _P. Persica_ var. _laevis_ Gray
5. _P. Persica_ var. _nucipersica_ Dippel _Handb. Laub._ =3=:606.
1893. (nectarine)
6. _P. Persica_ var. _platycarpa_ Bailey _Cyc. Am. Hort._ 1456. 1901.
(Flat Peach, Peento)
7. _Amygdalus Persica_ Linnaeus _Sp. Pl._ Ed. =1=:472. 1753.
8. _A. Persica_ var. _nucipersica_ Linnaeus l. c. 676.
(nectarine)
9. _A. nectarina_ Aiton _Hort. Kew_ Ed. =2=, =3=:194. 1811.
(nectarine)
10. _A. Nuci-persica_ Reichenbach _Fl. Germ. Exc._ 647. 1832.
(nectarine)
11. _A. laevis_ Dietrich _Syn. Pl._ =3=:42. 1852. (nectarine)
12. _Persica vulgaris_ Miller _Gard. Dict._ Ed. =8=: No. 1. 1768.
13. _P. nucipersica_ Borkhausen _Forstb. Beschrb._ 205. 1790.
(nectarine)
14. _P. laevis_ De Candolle _Fl. Fran._ =4=:487. 1805. (nectarine)
15. _P. platycarpa_ Decaisne _Jard. Fr. Mus._ (Pechers) 42. 1872-75.
(Flat Peach, Peento)

Tree low, attaining a height of thirty feet, diffuse,
open-headed, broad-topped, often without a central leader;
trunk at maturity sometimes a foot in diameter; bark dark
reddish-brown, in old trees rough and scaly; branches
spreading, slender and sometimes drooping; twigs round, rather
slender, glabrous, glossy green changing to shades of red, with
numerous, large or small, conspicuous, usually raised lenticels.

The leaves are alternate, simple, four to seven inches long,
one to two inches wide, broad-lanceolate or more often
oblong-lanceolate; upper surface dark green, smooth, dull or
shining, some rugose along the midrib; lower surface paler,
with little or no pubescence; apex long-tapering, base abrupt
or acute; margins coarsely or finely serrate, or crenate,
sometimes doubly toothed, teeth tipped with glands or sometimes
glandless; petioles stout, from a quarter-inch to an inch long,
grooved, glandless or more often with from one to eight globose
or reniform glands, sometimes mixed, a part of which may be on
the base of the leaf.

The flowers develop from scaly buds on the wood of the
previous season; flower-buds plump, conical or obtuse, free
or appressed and usually appearing before the leaves; flowers
of two distinct sizes, with some intermediates, the smaller
size ranging under an inch in diameter, the larger, an inch
and a half or more; the floral color ranges from an occasional
pure white through shades of pink to deep red; fragrant and
always pleasantly so; pedicels very short, sometimes seemingly
wanting, glabrous, green; calyx-tube urn-shaped, usually smooth
but sometimes pubescent without, green overlaid with red
outside, greenish-yellow or dark orange within; calyx-lobes
five in number, short, broad, glabrous within, pubescent
without; petals ovate, five in number, rounded at the apex
which is sometimes notched, tapering to a claw, sometimes
notched at the base; stamens twenty to thirty, about one-half
inch long, slender, distinct, usually colored; anthers yellow;
ovary sessile, pubescent, one-celled, surmounted by a simple
style which is terminated with a small stigma, the whole pistil
equaling the stamens in length or longer.

Fruit a fleshy drupe, sub-globular but much modified in shape
and size under cultivation; suture usually distinct; cavity
well marked, abrupt; apex with a mamelon or mucronate tip;
color varying from greenish-white to orange-yellow, usually
with a red cheek on the side exposed to the sun, sometimes
covered with red; very pubescent except in the nectarine;
skin adherent or free from the pulp; flesh greenish-white or
yellowish, often stained with red at the pit, occasionally red,
sweetish, acidulous, aromatic; stone free or clinging, elliptic
or ovoid, sometimes flat, compressed, pointed; outer surfaces
wrinkled and pitted, inner surfaces polished; ventral and
dorsal sutures grooved or furrowed, sometimes winged; the seed
almond-like, aromatic, bitter.

The characters given in the foregoing description are those of the cultivated peach--the consummate fruit of _Prunus persica_. The generic name, Prunus, is the ancient Latin name of the plum, _Prunus domestica_, the type species. The specific name, _persica_, commemorates the old belief that the peach came from Persia. The common name, peach, in English, as in most European languages, is a derivative from _persica_. Amygdalus, found several times in the synonomy, is the Syrian name of the almond. The drupe-fruits are put in two, three and sometimes four genera by various botanists but in the fruit-books issued by this Station, following most botanists and pomologists, all are put in a single genus, Prunus. Such lumping of several distinct fruits into one genus has its disadvantages but the several fruits cannot be reasonably separated because outliers closely connect all. Hybridization between the cultivated stone-fruits adds to the perplexities of classification.

_Prunus persica_ is variously divided by botanists and pomologists. Quite commonly two botanical varieties of edible peaches are split off, as shown in the synonomy, to separate the nectarine and the flat peaches from the pubescent and globular peaches. But these sub-species, originating over and over in the case of the nectarine as a bud or seed-mutation and the flat peaches probably having originated as a mutation, are not more distinct from the parent species than the red-fleshed sorts, the snowball peaches, the Yellow Transvaals from South Africa, the nippled peach, the cleft peach, the beaked peach, the winter peaches of China, or the pot-grown dwarfs from China; in fact, are not more different from other peaches than a clingstone is from a freestone, a yellow flesh from a white flesh or a large-flowered from a small-flowered sort. All constitute merely pomological groups, which, more and more, are becoming interminably confused by hybridization.

We name but one sub-species of _Prunus persica_, and that doubtful. Mr. Frank N. Meyer of the United States Department of Agriculture has recently introduced into the United States cuttings of a wild peach from the province of Kansu, China, which he thinks has horticultural value. The peach is _Prunus persica potanini_ Batalin (_Act. Hort. Petrop._ =12=:164. 1892) which Mr. Meyer describes as follows:[168]

"A wild peach of the _davidiana_ type, but differing from it in various points. Collected at the base of sheltered mountains at an elevation of 4300 feet. A tall shrub or even small tree, up to 30 feet in height, bark of stem or trunk dark reddish-brown and quite smooth in the younger shoots; leaves like those of _Amygdalus davidiana_ but often broader in the middle and always less pointed. Fruits of round-elongated form; skin covered with a heavy down, no edible flesh; stones of elliptical shape, grooves longer than in _A. davidiana_, shells very hard and thick, kernels elongated and relatively small. Found growing at elevations from 4000 to 7000 feet, in side valleys away from the Siku river; thrives especially well in sheltered and warm mountain pockets. Of value especially as a stock for stone-fruits and possibly able to stand even more dry heat than _A. davidiana_; also recommended as an ornamental spring-flowering tree, especially for the drier parts of the United States. Chinese name _Mao t'ao_, meaning 'hairy peach.'"

There are many ornamental forms of the peach-tree--sorts with single or double flowers, white, pink or red in color, normal, red or variegated foliage and standard or dwarf trees. The best-known named ornamental peaches are _camelliaeflora_ with large, carmine flowers and its sub-variety, _plena_, with double flowers; _versicolor_ with different colored flowers on branches of the same tree; _atropurpurea_ with brownish-red foliage; _foliis rubris_, similar or possibly the same as the preceding, the color in both extending to the fruit; _magnifica_, a semi-double with brilliant carmine-crimson flowers; _pyramidalis_, a pyrimidal form; _pendula_, a weeping peach; and still others, of the distinctness of which we cannot be certain, as _dianthi-alba-plena_, _rubro-plena_, and _coccineo-plena_. With these ornamentals we are not to be further concerned.

Of Japanese garden-forms the following varieties have been described: _P. Persica_ var. _densa_ Makimo _Tokyo Bot. Mag._ =16=:178. 1902. _P. persica_ var. _vulgaris_, f. _stellata_ Makimo l. c. =22=:119. 1908. _P. Persica_ var. _vulgaris_, f. _praematura_ Makimo l. c. =22=:119. 1908.

Species are but convenient groups, their limits reflecting the judgment of the species-maker. Were the authors of this text to divide _Prunus persica_, the cleavage lines would be other than those indicated in the foregoing paragraphs. _Prunus persica_ might be divided, though there is no intention of furthering confusion by the addition of new names, into two species. One would include the white-fleshed, clingstone peaches, with large flowers and calyx greenish-yellow inside; the other the yellow-fleshed, freestone peaches, with small flowers and calyx-cups orange inside. Primitive forms in China indicate such a division, the evolution of varieties suggests it and the present disposition of the characters named as separating these theoretical species attest the reasonableness of such a separation. The primitive forms have been described and the descent of varieties may be traced in the last two chapters, so that we need only amplify the statement as to the present disposition of characters.

The characters in the two hypothetical species have been thoroughly shuffled by hybridization but even if there is not correlation, as there certainly is between color in calyx-cup and color of flesh, it might be expected that those associated in the primitive plant, the Adam of the race, would, despite the shuffling, still be most often associated. What are the facts? In the Station orchard are 109 white-fleshed peaches; 40 per ct. of these are semi-cling or clingstones leaving 60 per ct. nearly or quite free (there is constant selection for freestones); 64 per ct. have large flowers; all have calyx-cups yellowish-green inside. There are in this orchard 106 yellow-fleshed peaches; but 17 per ct. of these are cling or semi-cling, the remainder being either quite free or nearly so; 73 per ct. have small or medium-sized flowers; all have calyx-cups deeply colored with orange inside.

Similarities in characters indicate so close a relationship between the almond and the peach that one might well suspect many hybrids between the two. Yet there appear to be but few clear cases of peach and almond crosses. Knight[169] reports crossing the two, the doubtful results of which led him to believe, as we have seen, that the peach is but a modified almond. Several such crosses are indicated in botanical literature[170] but whether all refer to one or several supposed crosses there is no way of knowing--probably to one. The almond blooms so much earlier than the peach that crosses could hardly occur in nature. A hybrid between the two from which could be evolved a late-blooming almond is a consummation to be wished.

THE NECTARINE

The nectarine is a hairless peach. The tree differs in no respect from that of the peach and besides the absence of pubescence the only other distinguishing marks between the fruits are smaller size, firmer flesh, greater aroma and a distinct and richer flavor in nectarines. Even the varieties of the two fruits correspond in characters. Thus, there are clingstone and freestone sorts of each; both may have red, yellow, or white flesh; the flowers of both may be large or small; nectarine leaves, in one variety or another, show all the variations in glands and serrations known to the peach; and the stones and kernels are indistinguishable. There seem to be no records so far, however, of flat or beaked nectarines, abnormalities each represented in several varieties of peaches. The two fruits are adapted to the same soil and climatic conditions and wherever the peach is grown, the world over, the nectarine is found.

The established history of the nectarine goes back 2000 years and then merges into that of the peach. Despite the fact that De Candolle[171] "sought in vain for a proof that the nectarine existed in Italy in the time of ancient Rome," we are convinced that Pliny's "duracinus" is the nectarine. Matthiolus[172] in 1554 discusses Pliny's statements concerning the kinds of peaches at length and concludes that the author's "duracinus" is the peach. Dalechamp, in 1587, and J. Bauhin, in 1650, both describe nectarines after which botanists and pomologists invariably include this fruit. In the Sixteenth and Seventeenth Centuries the nectarine was called "nucipersica" because it resembled in smoothness and color of the outer skin as well as in size and shape, the walnut. "Nectarine," the meaning of the word obvious, appears first to have been used for this fruit, in the English language at least, by Parkinson in 1629 who describes six varieties[173] and gives us the information "they have been with us not many years." Gerarde, the great English herbalist, 1597, does not mention them. We find the nectarine first mentioned in America in 1722 by Robert Beverly in his _History of Virginia_, who, after discussing the culture of peaches, nectarines and apricots, says (pages 259, 260): "Peaches and nectarines I believe to be spontaneous, somewhere or other on that continent, for the Indians have, and ever had greater variety, and finer sorts of them than the English."

The nectarine is one of the most interesting phenomena in horticulture. It is the classical example of bud- and seed-variation, furnishing more instances of mutation, and these more instructive, than have yet come from any other fruit. Darwin, with the magnificent exhaustiveness which characterized his method, brought together in _Animals and Plants under Domestication_[174] a striking array of facts which leaves nothing to be added as to the manner in which the peach and nectarine are reciprocally reproduced the one from the other. He shows by numerous examples: (1) That nectarines may spring from peach-stones and peaches from nectarine-stones. (2) That peach-trees produce nectarines by bud-variation and nectarine-trees likewise produce peaches, and that either the nectarines or peaches so arising will come true to seed. (3) That either peach or nectarine-trees may produce individual fruits half-nectarine and half-peach. (4) A case is cited of a nectarine tree bearing a half-and-half fruit and subsequently a true peach.

It must be noted that in all of the variations so far recorded there are no intermediate forms between the two fruits. The peach produced in these bud-variations is a peach and nothing but a peach; the nectarine, a nectarine and nothing but a nectarine. Even in those remarkable phenomena, of which several are recorded, in which the fruits are divided into halves or quarters, one or more segments being peach and one or more nectarine, there can be no mistake as to peach and nectarine in pubescence, color or flavor. The nectarine from the peach, thus becomes as clear-cut a case of discontinuous variation as can be. If we accept the mutation theory of the origin of species--new species arising suddenly at a single step--the nectarine is a species in process of birth.

As yet we are entirely ignorant in regard to the conditions under which the peach or the nectarine sports, the one producing the other. It is wholly a natural phenomenon, for no one has been able to cause the peach to produce the hairless form or the nectarine to bring forth a downy fruit. The relations of the two fruits have furnished a fertile field of inquiry for over a century but the problem is one of those mysterious ones in which there are many facts that cannot be fitted into a theory, so that our ignorance is as profound now as ever. There are, however, several theories which, without going into full detail, need to be stated.

The oldest notion is that the production of a nectarine on a peach-tree is due to the direct action of pollen from some nearby nectarine-tree on the ovary of the peach. This theory, wholly at variance with present knowledge, is also discredited by the many instances in which the sports occur when the two fruits are not growing in the same neighborhood or even region. Thus, within ten years, several cases of nectarines on peach-trees have occurred in this State where the nectarine is scarcely known. Besides, crossing these fruits shows no direct effect of pollen--as is true with nearly all other plants. Still further, when a branch of a peach has borne a nectarine it usually goes on year after year producing nectarines; and certainly impregnation of a flower by foreign pollen could not so profoundly modify a branch. There is so little foundation for this belief that it would not be mentioned were it not that many fruit-growers still look to the action of pollen as the explanation of the phenomenon.

Another, and a much more probable explanation, is that every sporting peach or nectarine-tree is a more or less remote hybrid. There is a growing belief that species are fixed and that crossing is the only source of new seed- or bud-forms. Certainly all who have crossed plants in any considerable numbers know that hybridity is at least one cause, and a frequent one, of mutations. It is possible that sometime in the past the peach and the nectarine were crossed, the offspring showing no trace of the cross, and that now there is an occasional disassociation of the characters brought together by such crossing. There are several objections to this hypothesis. One is that two forms sufficiently distinct to induce so striking a variation as a nectarine from a peach, must have differed in tree as well as in fruit-characters and that these differences would crop out just as smoothness of fruit so frequently does. Another, and less potent objection, is that the nectarine has never been found wild, that it never becomes naturalized, that it is shorter-lived and less vigorous and behaves in general like an artificial plant.

The third, and at present the most acceptable theory, is that we have in the nectarine from the peach what De Vries calls a retrogressive mutation. That is, an active character, in this case pubescence on the fruit, becomes latent and appears to be lost--a type of mutation frequent among cultivated plants. The nectarine, then, is a peach with one character subtracted. When the nectarine yields a peach, the character is restored. The one is a negative, the other a positive step; one is retrogressive, the other progressive mutation. The speculations as to what causes these mutations are as yet too vague to be profitable. Probably we can never make use of the cause by which mutations arise or of the conditions leading to them until we can induce these strange variations. That they are due to disturbances in the processes of cell-division is the theory now current--sufficiently comprehensive and sufficiently vague to be a most convenient explanation, at any rate.

Nectarines do not attain the perfection in New York reached west of the Rocky Mountains. The trees, possibly, are a little less manageable in the orchard, less vigorous and certainly more susceptible to pests. Nectarines, in particular, suffer more than peaches from the scourge of the crescent sign, curculio, a pest which finds all smooth-skinned stone-fruits much to its taste and the nectarine more than others. Then, too, whether fresh, canned or dried, fruit-buyers in America prefer the peach. This discrimination in favor of the peach is largely due to lack of knowledge of the nectarine, which, though different from the commoner fruit, is equally delectable, fresh or preserved, and certainly is a handsomer product preserved either by canning or evaporating. Indeed, the dried nectarine, with its beautiful, translucent, amber hue is the most attractive of all cured fruits. The nectarine-industry, however, belongs to California, where all conditions favor production, canning and curing.

PRUNUS DAVIDIANA (Carrière) Franchet

_P. Davidiana_ Franchet _Nouv. Arch. Mus. Paris_ ser. 2,
=V=:255 (_Pl. David._ =1=:103). 1883.

_Persica Davidiana_ Carrière _Rev. Hort._ 74. 1872.

_Prunus Persica_ var _Davidiana Maximowicz Bul. Acad. Sci. St.
Petersbourg_ =29=:81; _Mel. Biol._ =11=:667. 1883.

Tree attaining a height of twenty-five feet on the Station
grounds, vigorous, upright, with slight spreading tendency,
dense-topped, hardy in tree but not in flower-bud,
unproductive; trunk stocky; branches thick, smooth,
bronze-colored; branchlets slender--inclined to rebranch, long,
with rather short internodes, ash-gray mingled toward the base
with dark brown, glabrous, with inconspicuous, small, slightly
raised lenticels.

Leaves five and one-half inches long, one and one-eighth inches
wide, curled downward, oval to obovate-lanceolate, thick; upper
surface smooth, dull, dark green; lower surface grayish-green;
margin coarsely serrate, tipped with reddish-brown glands;
petiole five-eighths inch long, glandless or with one or two
small, globose, reddish glands at the base of the leaf.

Flower-buds tender, small, pointed, plump, appressed,
brownish-red; flowers appear very early, a few days earlier
than _Prunus tomentosa_, usually on short spurs; blossoms one
and five-eighths inches across, whitish, tinged with pale
pink near the margins, well distributed, usually singly;
pedicels short, glabrous, green; calyx-tube reddish-green,
orange-colored within, obconic, glabrous; calyx-lobes long,
narrow, glabrous within and without; petals widely spaced,
oval, shallowly dentate, tapering to long, white claws;
filaments shorter than the petals; pistil red, heavily
pubescent at the ovary, as long as the stamens.

Fruit less than one inch in diameter, nearly spherical; cavity
medium in width and depth; suture shallow, deeper toward the
base; apex mucronate; color grayish-white turning yellow
at maturity; pubescence downy; skin wrinkles and roughens
before maturity and soon decays; flesh very thin, rather dry,
tasteless and insipid, lacking almost entirely the flavor of
the peach; not edible; stone separates from the pulp readily
even before ripe, nearly spherical, plump, very blunt at base
and apex; surfaces deeply pitted.

Father David's peach, _Prunus davidiana_, has been grown in Europe since 1865 as an ornamental, seeds of it having been sent from China to France in that year by Father David, a missionary traveler.[175] The species is described as flowering in America in the Arnold Arboretum as early as 1888,[176] seeds from which the trees grew having been sent from China. Some ten or twelve years ago the species was distributed by the United States Department of Agriculture, trees being received at this Station in the spring of 1906. Meanwhile, agricultural explorers representing this country in China have discovered that the species is much used by the Chinese as a stock upon which to work other species of Prunus. Whereupon, new distributions were made through seeds and plants to nearly every fruit-growing state in the Union. We are, therefore, now able to speak of the behavior of the Davidiana peach in America with some degree of confidence as to its future as a stock for peaches. But, first, a word as to its habitat and uses in China.

The several importations of seeds recorded by the United States Department of Agriculture seem all to have been made from the province of Chili in China and from the cities of Pekin and Tientsin in the neighborhood of which the tree is commonly found wild. According to Bretschneider,[177] the species was first discovered by Bunge near Peking in 1831 who took it to be an almond. The same authority says that Father David's seeds came from wild trees growing in the mountains near Jehol, and that the species is much cultivated in the gardens of Peking, there being two varieties, one with rose-colored and the other with white flowers. At the time of its introduction into Europe, it was considered, by some, the wild form of the cultivated peach. The fruit of David's peach is not edible and peach-growers would have but passing interest in the species as a very attractive ornamental were it not for the fact that it is a common and most valuable stock, used for centuries in China for several of the stone-fruits.

It is, then, with a view to its fitness as a stock that the Davidiana peach must be discussed. Its characters in several respects indicate that it may make an invaluable stock in America as it has long been in China. For this purpose it seems possible to use it equally well for several stone-fruits.

As it grows on the Station grounds the most experienced fruit-grower cannot guess whether _Prunus davidiana_ is a peach, nectarine, almond, apricot or plum. As we shall show later, too, it hybridizes with several other species of its genus. Its similarities to all of these stone-fruits give a clue to its value as a stock--it may be used for all. It is the commonest stock for all of these fruits in parts of China and is sometimes used for the cherry as well. It is reported by the United States Department of Agriculture[178] to have been tried in commercial plantings of peaches, plums, apricots and almonds in California and Texas and for all is "unusually promising."

The trees are vigorous, healthy, hardy, and resistant to drouth. Consorted with any stone-fruit it should impart these qualities in some degree to the resulting tree. On the Station grounds, _Prunus davidiana_ is growing with vigor and health despite the fact that in the ten years of its existence here we have had all but record-breaking extremes of cold, heat, drouth and rain--a decade long to be noted for its extremes of weather. It seems to stand the heat of Texas, and in Minnesota has withstood cold as low as forty degrees below zero, a temperature which kills commercial varieties to the ground. It cannot be fruited, however, in cold climates as its buds swell quickly with rises of temperature and succumb to subsequent cold; neither will it fruit in regions of late frost since it is one of the earliest species in the genus Prunus to flower. In Texas and southern California, according to the United States Department of Agriculture, it is proving resistant to drouth and in the latter region to alkali as well. In very dry and exposed places, it is said to lose its tree-characters and to become a thrifty shrub.

Present nursery practices in growing peaches are unsatisfactory in the extreme. More and more, pits from canneries are being planted for stocks. The pits come from a great diversity of varieties and the resulting seedlings are variable in vigor, health, size and capacity to take the bud. Should no unsurmountable weaknesses appear in _Prunus davidiana_ it is almost certain that its seedlings will be more satisfactory as stocks for the peach than those from either cannery pits or from pits grown on southern wild trees. The trees do not fruit well in this climate, even when buds and flowers escape the cold, possibly because of infertility of bloom, and for this reason, the chief objection so far, some favorable region would have to be discovered in which to grow the pits.

As one might suspect from its similarities to the several stone-fruits, _Prunus davidiana_ gives promise of being a go-between in hybridization. I. V. Mijurin, a noted Russian hybridist of Kozloo, Russia, has crossed the Davidiana peach and the dwarf almond, _Prunus nana_, with the idea of getting a hardy fruit for central Russia. The resulting offspring, according to Mr. F. N. Meyer,[179] looks in tree like the peach-parent but the fruit is more like that of the almond-parent. The fruit of the hybrid is inedible but the plant is a handsome ornamental. Mr. Mijurin states that while neither of the two parents will hybridize with the common peach, this hybrid does. _Prunus davidiana_, then, like the Sand Cherry of the Western Plains, may prove to be a valuable go-between in hybridizing species of Prunus.

The fruit has no comestible value. It is small, less than an inch in diameter, nearly round, very downy, yellow at maturity, with thin, dry, tasteless flesh which parts readily from the stone even before fully ripe. As if to complete its worthlessness as an edible product, it begins to shrivel as maturity approaches and soon decays. In fruit, even more than in tree, it is an intermediate between the peach and the almond.

A word must be said as to the merits of _Prunus davidiana_ as an ornamental. It is the first harbinger of spring in the great family to which it belongs, bursting into a profusion of white or pinkish flowers with the approach of warm weather even before forsythias are in flower. Its thickly set, erect branchlets are wands of pinkish-white two feet in length, making a handsome tree and furnishing beautiful cut-flowers. If grown for its flowers, however, one must be content in northern climates to have it in bloom only about one season out of three but even so it repays culture. The Chinese cultivate dwarf specimens, possibly a dwarf form, for winter-flowering and the plant, it would seem, would readily lend itself to winter-forcing in American floriculture. The tree, quite aside from its flowers, is handsome at all times. A form with pure white flowers is a very desirable ornamental.[180] On the Station grounds this white-flowering peach has a fastigiate habit of growth and resembles somewhat a small Lombardy poplar.

PRUNUS MIRA Koehne.

_P. mira_ Koehne _Plant_. _Wilson._ Pt. 2, No. =4=:272. 1912.

Tree thirty feet in height; trunk sixteen inches in diameter;
branches very smooth, those of the current year's growth green,
the older ones dark reddish-yellow; flowering-season short;
stipules lacking or obscure; petioles five-sixteenths to
ten-sixteenths of an inch long, with from two to four glands
toward the apex, the glands broadly elliptical, disc-shaped;
leaf at the base usually roundly lanceolate, two to four
inches long, nine-sixteenths to one and one-sixteenth inches
broad, gradually narrowing toward the apex; margin broadly
crenulate-serrulate, tapering upward without division; teeth
crowned with small, soot-colored, mucronate glands; upper
surface clear green, glabrous; lower surface paler, villous
along both sides of the lower ribs and the rest glabrous; veins
on both sides twelve to sixteen, the veinlets somewhat raised
on the under side.

The pedicels of the single or twinned fruits two-sixteenths to
three-sixteenths of an inch long, very thick, glabrous; drupes
somewhat dry, sub-globose, one and one-eighth inches long,
one inch in diameter, densely tomentose, edible; stone ovate,
somewhat compressed, dimensions three-fourths by one-half by
three-eighths inches; dorsal suture keeled, the ventral surface
covered with narrow ridges, the ridges at the base of the keel
nearly disappearing, the rest inconspicuous.

_Prunus mira_ is a new peach discovered in China by Mr. E. H. Wilson of the Arnold Arboretum. The foregoing technical description is a translation from the original description by Koehne. Mr. Wilson describes for _The Peaches of New York_ the outstanding botanical and horticultural characters of _Prunus mira_ as follows:

"_Prunus mira_ is a small bushy tree, growing about 6m. tall, with a trunk about 1m. in girth and a crown some 8m. through. The branches are relatively slender and the branchlets twiggy, and these, together with the narrow, lance-shaped, long-pointed leaves, give the plant a very distinct appearance. The fruit is roundish oval, about 4.5 cm. high and 3.5-4 cm. broad, downy on the outside, with white flesh and a free stone. The flavor is the same as that of fruits from the semi-wild plants of the Common Peach (_P. Persica_). The stone is 2 to 2.2 cm. high and 1.3-1.4 cm. broad, and in shape is flattened ovoid and pointed. The flowers are unknown to me.