The Genus Pinus

THE FLOWERS. Plate III, figs. 33-39.

The flowers in Pinus are monoecious, the pistillate in the position of a long shoot, taking the place of a subterminal or lateral bud, the staminate in the position of a dwarf-shoot, taking the place of a leaf-fascicle but confined to the basal part of the internode.

Pistillate flowers are single or verticillate. On multinodal shoots they are often multiserial, appearing on two or more nodes of the same spring-shoot (fig. 33). On uninodal shoots they are necessarily subterminal (fig. 34), the lateral pistillate flower being possible only on multinodal shoots (fig. 35) where it is often associated with the subterminal flower (fig. 33). Like the multinodal shoot, on which its existence depends, the lateral pistillate flower cannot be employed for grouping the species. It is merely the frequent, but not the essential, evidence of condition of growth that is more perfectly characterized by the shoot itself.

Staminate catkins are in crowded clusters, capitate or elongate (figs. 36, 37), but with much variation in the number of catkins in each cluster. In P. rigida I have found single catkins or clusters of all numbers from two to seventy or more. In P. Massoniana and P. densiflora a cluster attains such unusual length (fig. 37) that this character becomes a valuable distinction between these species and P. sinensis, which has short-capitate clusters. The catkins differ much in size, the largest being found among the Hard Pines.

In the connective of the binate pollen-sacs there is a notable difference (figs. 38, 39), the smaller form being characteristic of the Soft Pines. But this is not invariable (excelsa, sylvestris, etc.), and the absence of complete data does not permit an accurate estimate of its importance.

THE CONELET. Plate III, figs. 40-45.

After pollination the pistillate flower closes and becomes the conelet, the staminate flowers withering and falling away. The conelet makes no appreciable growth until the following year. Like the pistillate flower it may be subterminal or lateral, but a subterminal pistillate flower may become a pseudolateral conelet by reason of a summer-growth (fig. 40-a). Such a condition may be recognized on the branchlets of the present, and of the previous year (fig. 40-b), by the very short internode and short leaves beyond the fruit.

The conelet offers some distinctions of form, of color, and of length of peduncle, while in some species (sylvestris, caribaea, etc.) its reflexed position is an important specific character. The most important distinctions, however, are found in its scales, which may be

THE CONE. Plate IV.

The cone of Pinus shows great differences of color, form and tissue; these are useful for specific and sectional distinctions, while the gradual change from the primitive conditions of the Cembrae to the elaborate form, structure and mode of dissemination of some serotinous species are obvious evidence of an evolution among the species of remarkable taxonomic range. A form new among Coniferae appears, the oblique cone, and a new condition, the serotinous cone, both appearing at first alone and, finally, in constant association.

COLOR OF THE CONE.

With few exceptions the color of the ripe cone may be classified under one of the following shades of brown or yellow.

These colors may be paler or deeper. They may be obscured by a fuscous shade or may be modified by a dull or lustrous surface. The presence of two or more of these shades in a single species and the inherent difficulties of color description lessen the value of the character. Nevertheless certain allied species, such as P. nigra and Thunbergii, or P. densiflora and Massoniana, may be distinguished by the prevalent difference in the color of their cones.

DIMENSIONS OF THE CONE.

The cone is small, medium or large in different species, but varies greatly under the influences of environment or of individual peculiarities. The character possesses relative value only, for great variation is possible in the same locality and even on the same tree.

THE PEDUNCLE.

All conelets are pedunculate, but in some species the peduncle, even when long (patula), may become overgrown and concealed by the basal scales of the ripe cone. Articulation usually takes place between the peduncle and the branch, sometimes with the loss of a few basal scales which remain temporarily on the tree (ponderosa, palustris, etc.). With P. Nelsonii, and to a less degree with P. Armandi, there is articulation between the cone and its peduncle.

There are several species bearing persistent cones with no articulation. This condition appears in other genera, such as Larix and Picea, but without obvious significance. In Pinus, however, the gradual appearance of the persistent cone, for it is rare, common, prevalent or invariable in different species, and its essential association with the serotinous cone, suggest an evolution toward a definite end.

THE UMBO.

The exposed part of the scale of the conelet is the umbo of the ripe cone, a small definite area representing the earlier part of the biennial growth of the cone. The position of the umbo on the apophysis is the basis of Koehne's subdivision of the section Haploxylon.

Two other characters assist in establishing these subsections-the conelet, unarmed in Cembra, armed in Paracembra-the pits of the ray-cells of the wood, large in Cembra, small in Paracembra.

THE APOPHYSIS.

The apophysis represents the later and larger growth of the cone-scale. With a terminal umbo the margin of the apophysis is free and may be rounded (fig. 49) or may taper to a blunt point (fig. 52), and any extension of the scale is a terminal extension. With the dorsal umbo all sides of the apophysis are confined between other apophyses, and any extension is a dorsal thickening of the apophysis or a dorsal protuberance. The outline of an apophysis with a dorsal umbo is quadrangular, or it is irregularly pentagonal or hexagonal, the different forms depending on the arrangement of the contiguous scales, whether of definite or indefinite phyllotactic order, a distinction to be considered later.

The two positions of the umbo result from the relative growth of the dorsal and ventral surfaces of the cone-scale. With the terminal umbo the growth of both surfaces is uniform, with the dorsal umbo the growth is unequal. A true terminal umbo rests on the surface of the underlying scale, although several species with terminal umbos show the first stages of the dorsal umbo. The umbo of P. Lambertiana or of P. flexilis does not touch the surface of the scale below, and a small portion of the under side of the apophysis is brought into view on the closed cone. The cone of P. albicaulis (Plate VIII, fig. 90) shows all degrees of development between a terminal umbo near the apex of the cone and a dorsal umbo near its base.

The growth of the apophysis may be limited and constant (strobus, echinata, etc.) or exceedingly variable, ranging from a slight thickness to a long protuberance (pseudostrobus, montana, etc.). The protuberance is usually reflexed from the unequal growth of the two surfaces. With the terminal umbo the protuberance lengthens the scale, with the dorsal umbo it thickens the scale. It is sometimes a specific character (ayacahuite, longifolia) appearing on all cones of the species, sometimes a varietal form, associated in the same species with an unprolonged apophysis (sylvestris, montana).

On different parts of the same cone, base, centre or apex, the dimensions of the apophyses differ, but at each level the scales may be uniform on all sides of the cone. That is to say, the cone is symmetrical with reference to any plane passing through its axis. This, the symmetrical cone, is characteristic of all other genera of the Abietineae, and is invariable among the Soft Pines and in many Hard Pines (figs. 47, 48, 52, 54). But among the Hard Pines there is gradually developed a new form of cone with smaller flatter apophyses on the anterior, and larger thicker apophyses on the posterior surface. This is the peculiar oblique cone of Pinus (figs. 50, 51, 53), symmetrical with reference to one plane only, which includes the axis of both cone and branch. The oblique cone is a gradual development among the...