The Genus Pinus

These are the Nut Pines, growing on the arid slopes and table-lands above the great plateau of northern Mexico and its extension into the southwestern United States. There are three distinct species.

A broad tree with a round head, similar in size and form, but not in ramification, to the cultivated Apple-tree; growing on arid slopes and table-lands. Its eastern limit is in southwestern Wyoming, central Colorado, Texas, western Tamaulipas and northwestern Vera Cruz. It ranges over Utah, Nevada, Arizona and the northern states of Mexico to the southern Sierras of California and to the northern and southern extremities of Lower California. It is recognized by its small cone, which expands, when open, into an irregular flat aggregate of loosely attached scales. The leaves are shorter than those of the other Pines of this group.

The cone of this species always retains its peculiar character. The variations are mainly in the number of leaves in the fascicle. On this character this Nut Pine is divided by many authors into four species—cembroides, with three slender leaves—edulis, with two stout leaves—monophylla, with one leaf and—Parryana, with four stout leaves. But there are intermediate forms that may be either cembroides or edulis, edulis or monophylla etc., and Voss's reduction of the four to a single species with three varieties seems to be justified (Mitt. Deutsch. Dendrol. Ges. xvi. 95).

Fig. 130, Cone, cone-scale and seed. Fig. 131, Open cone. Fig. 132, Branchlet with leaves and magnified leaf-section.

A small bushy tree with long slender branchlets, clear gray cortex, persistently smooth except on the lower part of the trunk, and glaucous-green foliage. It grows along water-courses, dry in autumn and winter, from southern Coahuila to central Hidalgo, and is associated with P. cembroides, from which it may be distinguished by its longer leaves and much longer cylindrical cone.

Fig. 127, Cone, cone-scale and seed. Fig. 128, Branchlet with leaves. Fig. 129, Magnified leaf-section.

A small bushy tree with long pliant branches, clear gray cortex all over the limbs and trunk, and sparse gray-green foliage. It grows, together with P. cembroides, on the lower slopes of the northeastern Sierras of Mexico, near the boundary between the states of Tamaulipas and Nuevo Leon. It is apparently confined to a small area near the latitude of the city of Victoria, the capital of Tamaulipas, where its nuts are often exposed for sale.

In many characters this species is unique. It can be recognized at once by the connate leaves that form the fascicle or by the remarkable stout curved peduncle of its cone. Such seeds as I have seen differ from those of P. cembroides by a reddish area at one end, but this can be seen with fresh seeds only.

Fig. 124, Cone, cone scale and seed. Fig. 125, Branchlet with leaves. Fig. 126, Magnified section of a leaf-fascicle.

These Asiatic Nut Pines are alike in leaf and cortex as well as in the peculiar seed-wing. The last often remains in the cone after the nut falls. The mechanical nature of this adhesion is apparent in P. Gerardiana, where the wing adheres not to its own, but to the adjacent scale. The two species are alike in their leaves but distinct in their cones and seeds.

A tree cultivated about the temples of China and recently found by Wilson growing on the mountains of Hupeh. The earlier parti-colored bark changes to chalky white on old trunks, by which the tree is recognized from a great distance. The stem of the tree is often multiple by the vertical growth of some of the lower branches. It is very hardy and is cultivated in Europe and America, although these cultivated trees are not yet of sufficient age to show the remarkable white trunk.

Fig. 138, Cone and cone-scale with adhering wing. Fig. 139, Seed and wing. Fig. 140, Leaf-fascicle and magnified leaf-section. Fig. 141, Parti-colored bark. Fig. 142, Tree with white trunk.

A tree of the northwestern Himalayas found on the borders of Cashmere and Thibet and in Kafiristan and north Afghanistan, and so highly prized for its nuts that it is rarely felled for its wood. It grows in dry regions and rarely attains a height of 20 metres. Attempts to cultivate this species, even in the milder parts of Great Britain, have generally failed.

The apophysis of the cone varies much in prominence (figs. 134, 135), but the peculiar seed is invariable and quite unlike that of any other Pine. The general color of the trunk at a distance is silver-gray.

Fig. 133, Cone. Fig. 134, Cone-scale with adhering seed-wing. Fig. 135, Cone-scale of flatter form. Fig. 136, Seed and wing. Fig. 137, Leaf-fascicle and magnified leaf-section.

The two species known as Foxtail Pines are alike in their short entire falcate leaves, persisting for many years and forming long dense foliage-masses. They differ in the armature of their cones and in their seed-wings. The presence of both adnate and articulate wings in these closely related species suggests that these two forms of wing are not fundamentally distinct.

An alpine species growing often at the timber-limit. It is found in two distinct stations in California, on the northern Coast Range and on the southern Sierras. It is not often cultivated, but young plants may be seen in the Arnold Arboretum and in the Royal Gardens at Kew.

Fig. 147, Cone, seed and enlarged cone-scale. Fig. 148, Leaf-fascicle. Fig. 149, Magnified leaf-section. Fig. 150, A branch with persistent leaves.

A bushy tree, similar in foliage to the preceding species, growing at the timber-limit from Colorado through Utah, central and southern Nevada and northern Arizona into southeastern California, but separated from the nearest station of P. Balfouriana by an arid treeless desert. Engelmann (in Brewer and Watson, Bot. Calif. ii. 125) considered it to be a variety of P. Balfouriana.

Fig. 143, Cone. Fig. 144, Seed and enlarged cone-scale. Fig. 145, Leaf-fascicle and magnified leaf-section. Fig. 146, Conelet.

In this section there are a few species combining the essential characters of Diploxylon with important characters of Haploxylon. A subsection, Parapinaster, is established for these exceptional species.

This species grows at subtropical or warm-temperate altitudes in Mexico, from Oaxaca through the central and western states to southern Arizona and New Mexico. As it approaches the northern part of its range the leaves become thicker and more rigid and the number in the fascicle is reduced to 3 or 4 (var. chihuahuana, Shaw, Pines Mex. 14). Like P. rigida it sprouts freely along the branches and trunk, and stumps of felled trees put out shoots in great numbers. The species is easily recognized by the deciduous sheath and triennial cone.

Fig. 151, Branch with fruit of first, second and third years. Fig. 152, Leaf-fascicles. Fig. 153, Magnified leaf-section of the species. Fig. 154, Magnified leaf-section of the variety.

A remarkable Pine with long pendent bright green foliage, confined to the western states of Mexico and ranging on the mountains from southern Jalisco to the latitude of the city of Chihuahua. Each season's growth of leaves hangs from the branchlet like a long beard, from which the tree receives, in some localities, the name "Pino barba caida." In the herbarium the long leaves, deciduous sheaths, and the decurrent bases of the bracts, present a combination of characters not found in other species.

Fig. 155, Cone. Fig. 156, Cone. Fig. 157, Leaf-fascicle. Fig. 158, Magnified leaf-section. Fig. 159, Tree at Ferraria de Tula.

Of the three Pines of the Himalayas this species is the most important. It grows on the outer slopes and foot-hills from Bhotan to Afghanistan. The wood is used for construction and for the manufacture of charcoal, the thick soft bark is valuable for tanning, the resin is abundant and of commercial importance, and the nuts are gathered for food. The tree is not hardy in cool-temperate climates, but has been successfully grown in northern Italy.

It differs from P. canariensis in the usually protuberant apophysis of the cone, in the thick outer walls of the leaf-endoderm and in the nearly smooth walls of the ray-tracheids of the wood. In the dimensions of cone and leaf, in the dermal tissues and resin-ducts of the leaf and in the peculiar coloring of the seed-wing, the two species are alike.

Fig. 160, Cone. Fig. 161, Leaf-fascicle. Fig. 162, Magnified leaf-section.

A species confined to the Canary Islands, but cultivated in northern Italy. The stately habit of this tree is seen in Schröter's portrait (Exc. Canar. Ins. t. 15).

Fig. 163, Cone and seed. Fig. 164, Magnified leaf-section. Fig. 165, Habit of the tree.

A species of the Mediterranean Basin, from Portugal to Syria. Its northern limit is in southern France and northern Italy, but it is cultivated in the southern parts of the British Isles and is a familiar ornament of park and garden in southern Europe, and is valued for its peculiar beauty and for its large savory nuts. In wood anatomy as well as in the seed it agrees with the Gerardianae of the Soft Pines.

Fig. 166, Fruit of three seasons. Fig. 167, Cone-scales and seed. Fig. 168, Magnified leaf-section. Fig. 169, Habit of the tree.

Forty-two of the sixty-six species of Pinus are included in this subsection. As a group they are clearly circumscribed by several correlated characters and are more closely interrelated than the twenty-four species previously described. The distinctions of umbo and seed have disappeared. The umbo here is invariably dorsal, the seed-wing invariably articulate.

New forms, however, are gradually evolved—the seed with a thick wing-blade, the indurated oblique cone, the serotinous cone with its intermittent seed-release, and the multinodal spring-shoot. There are, moreover, new forms of leaf-hypoderm and a new position of the resin-duct.

Of these new characters, the thick wing-blade attains such proportions in the three species of the Macrocarpae that they can be grouped apart. But the characters that finally culminate in a lateral oblique serotinous cone are so gradually and irregularly developed that they offer no divisional distinctions. With the aid of wood and leaf characters, however, groups can be established which preserve the evolutionary sequence and, at the same time, the obvious affinity of the species.

The species of this subsection are very difficult, if not impossible, to classify by the usual method, which groups all species under a few characters assumed to be invariable and of fundamental importance. Such a method can be successfully applied to the Soft Pines and to some of the Hard Pines, but cannot be applied to all the Hard Pines without forcing some of them into unnatural associations.

To take an example, the group Pseudostrobus, characterized by pentamerous leaf-fascicles, appears in many systems. In this group are placed P. Torreyana and P. leiophylla. Another group, with trimerous fascicles, contains P. Sabiniana and P. taeda. Now there are no two species more obviously related by important peculiarities than P. Torreyana and P. Sabiniana; nevertheless they are, by this method, kept apart and associated with species which they resemble in no important particular.

An attempt is made here to avoid such incongruities. Groups X, XI and XII represent different stages of evolution. In the Lariciones the cone is symmetrical, and dehiscent and deciduous at maturity, while the spring-shoot is uninodal. In the Australes there is a similar cone, but the spring-shoot gradually becomes multinodal. In the Insignes the cone is oblique, persistent and serotinous, and the spring-shoot is multinodal.

These definitions state the degree of evolution attained by each group, but not all the species of a group conform exactly with its definition. In each group are species with a characteristic of another group. Among the Lariciones are a few species with both symmetrical and oblique cones, and two with persistent cones. Similar exceptions occur among the Australes. Among the Insignes are a few species with symmetrical cones, and two with cones that are rarely, if ever, serotinous.

There is, however, no difficulty in fixing the systematic position of these exceptional species through other characters which show their true affinity. They are placed with the species which they most resemble. Their exceptional characters are merely the evidence of the evolution that pervades and unites the groups. Therefore the definition of a group is not necessarily the exact definition of its species, and a species is placed in a group because all its characters, specific and evolutional, show a closer affinity with that group than with the species of any other.

This group represents the first stage in the evolution of the Hard Pines. All the species, like the Soft Pines, are uninodal and the cones are dehiscent at maturity, but the trend toward the serotinous species is shown in the occasional appearance of the oblique cone as a varietal form of a few species, and in the persistent cone of the last two species of this group.

All the species of this group are of the Old World except P. resinosa and P. tropicalis. These two are the only American Pines combining large pits with dentate tracheids, and are the only American Hard Pines with external resin-ducts of the leaf.

From Nova Scotia and Lake St. John this species ranges westward to the Winnipeg River and southward into Minnesota, Michigan, northern New York and eastern Massachusetts, with rare occurrence on the mountains of Pennsylvania. Under cultivation it is a beautiful tree, adapted to cold-temperate climates. It was considered by Loiseleur (1812) and by Spach (1842) to be a variety of P. nigra (laricio). The two species vary in the color of the cone, the anatomy of the leaves, the buds, and in the armature of the conelet. A fallen cone of this species is moreover usually imperfect from the loss of a few basal scales.

Fig. 170, Cone and enlarged conelet. Fig. 171, Leaf-fascicle and magnified leaf-section.

Growing at sea-level within the tropics and confined to western Cuba and the Isle of Pines. On the island it is associated with P. caribaea. This species needs no other means of identification than its peculiar leaf-section. Septal ducts are found in P. oocarpa, Pringlei, Merkusii and rarely in other species, but they never attain the extraordinary size that appears to be invariable in P. tropicalis.

Fig. 172, Cone and enlarged conelet. Fig. 173, Branch with leaves, much reduced. Fig. 174, Leaf-fascicle and magnified leaf-section. Fig. 175, Trees on the Isle of Pines.

The Chinese Red Pine is found in warm-temperate climates. It is native to southeastern China and follows the valley of the Yangtse River into Szech'uan. It has been confused by London with P. pinaster, which it resembles in no respect, by Siebold with P. Thunbergii, from which it differs in leaf-dimensions and in leaf-section, and by Mayr with his P. luchuensis, whose peculiar cortex and whose leaf-section has no counterpart among Chinese Hard Pines. Its nearest relative is P. densiflora, from which it differs in its longer leaves, in the color of its cone and in its conelet (Plate XX, figs. 176, 179).

Fig. 176, Cone and enlarged conelet. Fig. 177, Two leaf-fascicles. Fig. 178, Magnified leaf-section.

The Japanese Red Pine forms extensive forests on the mountains of central Japan. It is perfectly hardy in cold-temperate climates. Wild specimens of China, ascribed to this species, are forms of the variable P. sinensis. From P. Massoniana it differs in its shorter leaves and yellow cone, but particularly in the more prominent prickles and thicker scales of its conelet (figs. 176, 179).

Fig. 179, Cones and enlarged conelet. Fig. 180, Leaf-fascicles. Fig. 181, Magnified leaf-section and more magnified dermal tissues of the leaf.

A tree of great commercial value, with a very extended range, from Norway, Scotland and southern Spain to northeastern Siberia. A vigorous hardy species and extensively cultivated. The red upper trunk, characteristic of this Pine, is not invariable. The dark upper trunk is sufficiently common to be considered a varietal form (Mathieu, Flore Forest. ed. 4, 582). In various localities may be found trees bearing oblique cones, their apophyses showing various degrees of protuberance up to the extreme development represented in Loudon's illustration of the variety uncinata (Arb. Brit. iv, f. 2047). This cone is the beginning of the changes that culminate in species with oblique cones only. In P. sylvestris, however, the purpose of this form of cone is not apparent except in connection with this evolution.

Figs. 182, 183, Cones. Fig. 184, Leaf-fascicle, magnified leaf-section and more magnified dermal tissues of the leaf. Fig. 185, Habit of the tree.