mong the species of the genus.

Variation induced by environment finds familiar illustrations among the
species that can survive at the limits of vegetation and can meet these
inhospitable conditions by a radical change of all growing parts. Such
variations are mainly of dimensions, but, with some species, the number
of fascicle-leaves is affected and the shorter growing-season may modify
the cone-tissues. In Mexico and Central America are found extremes of
climate within small areas and easily within the range of dissemination
from a single tree. The cause of the bewildering host of varietal forms,
connecting widely contrasted extremes, seems to lie in the facile
adaptability of those Pines, which are able to spread from the tropical
base of a mountain to a less or greater distance toward its snow-capped
summit.

The peculiarities of individual trees that induce abnormally short or
long growths, the dwarf or other monstrous forms, the variegations in
leaf-coloring, etc., etc., are not available for classification, for
they may appear in any species, in fact in any genus of Conifers. These
variations are artificially multiplied for commercial and decorative
purposes. But inasmuch as they are repeated in all species and genera of
the Coniferae that have been long under the observation of skillful
gardeners, their significance has a broader scope than that imposed by
the study of a single genus.

PART II

CLASSIFICATION OF THE SPECIES

The following classification is based on the gradual evolution of the
fruit from a cone symmetrical in form, parenchymatous in tissue,
indehiscent and deciduous at maturity, releasing its wingless seed by
disintegration--to a cone oblique in form, very strong and durable in
tissue, persistent on the tree, intermittently dehiscent, releasing its
winged seeds partly at maturity, partly at indefinite intervals during
several years. This evolution embraces two extreme forms of fruit, one
the most primitive, the other the most elaborate, among Conifers.

Two sections of the genus, Soft and Hard Pines, are distinguished by
several correlated characters, and moreover are distinct by obvious
differences in the tissues of their cones as well as in the quality and
appearance of their wood.

With the Soft Pines the species group naturally under two subsections on
the position of the umbo, the anatomy of the wood and the armature of
the conelet. In one subsection (Cembra) are found thre