ygroscopic tissue of the cone-scales. The dry
conditions that open the cone and release the seeds cause the bifurcate
base of the wing to grasp the nut more firmly.

This articulate wing is found in P. aristata and in all Hard Pines
except P. pinea, longifolia and canariensis. The wing-blade is usually
membranous throughout, but in some species there is a thickening of the
base of the blade that meets the membranous apical part in an oblique
line along which the wing is easily broken apart. This last condition
attains in P. Coulteri and its associates a remarkable development.

Plate VI, fig. 72 shows the wingless seed of P. cembroides; fig. 73
represents the seed of P. flexilis, with a rudimentary wing; fig. 74
shows two seeds of P. strobus, intact and with the wing broken away;
fig. 75 represents the articulate wing, whose bifurcate base when wet
(fig. 76) tends to open and release the nut. When dry (fig. 77) the
forks of the base, in the absence of the nut, close together and cross
their tips; figs. 78, 79 show the peculiar reinforced articulate wing of
P. Coulteri.

Such wide variation in so important an organ suggests generic
difference. But here we are met by the association of the different
forms in species evidently closely allied. The two Foxtail Pines are so
similar in most characters that they have been considered, with good
reason, to be specifically identical; yet the seed-wing of P.
Balfouriana is adnate, that of P. aristata articulate. P. Ayacahuite
produces not only the characteristic wing of the Strobi, adnate, long
and effective, but also, in the northern variety, a seed with a
rudimentary wing, the exact counterpart of the seed of P. flexilis. In
both sections of the genus are found the effective adnate wing (Strobi
and Longifoliae) and the inefficient articulate wing (Gerardianae and
Pineae). A little examination of all forms of the seed will show that
they blend gradually one into another.

The color of the wing is occasionally peculiar, as in the group
Longifoliae. There is usually no constancy in this character, for the
wing may be uniform in color or variously striated in seeds of the same
species. The length and breadth of the seed-wing, being dependent on the
varying sizes of the cone-scale, differ in the same cone. They are also
inconstant in different cones of the same species, and of this
inconstancy the seed of P. ayacahuite furnishes the most notable
example.

[Illustration: PLATE VI