these progressive characters culminate in
mutual association in P. radiata and its allies. The result is a highly
specialized fruit that should convey taxonomic significance of some
kind.

With all serotinous species that I have seen, some of the trees open
their cones at maturity, others at indefinite intervals. That is to say,
the seed of a prolific year is not at the mercy of a single, perhaps
unfavorable season. The chances of successful germination are much
increased by the intermittent seed-release peculiar to these Pines. Such
a method of dissemination must accrue to the advantage of a species. In
other words, this intermittent dissemination and the oblique form of
cone with its perfected tissues all mark the highest development of the
genus.

THE SEED. Plate VI. Figs. 72-79.

The seed of Pinus contains an embryo, with the cotyledons clearly
defined, embedded in albumen, which is protected by a bony testa with an
external membranous spermoderm, produced, in most species, into an
effective wing. While the seed of other genera of the Abietineae shows
no striking difference among the species, that of Pinus is remarkably
variable, presenting alike the most primitive and the most elaborate
forms among the Conifers. These differences are valuable for the
segregation of kindred species and for some specific distinctions.

WINGLESS SEEDS.

With wingless seeds the main distinction is found in the spermoderm,
which is entire in one species only, P. koraiensis. In P. cembra it is
wanting on the ventral surface of the nut, but on the dorsal surface, it
is adnate partly to the nut, partly to the cone-scale. The nut of P.
albicaulis and that of P. cembroides are quite bare of membranous cover.
The spermoderm of P. flexilis is reduced to a marginal border, slightly
produced into a rudimentary wing adnate to the nut.

THE ADNATE WING.

In P. strobus, longifolia and their allies and in P. Balfouriana the
spermoderm is prolonged into an effective wing-blade from a marginal
adnate base like that of P. flexilis. This adnate wing cannot be
detached without injury.

THE ARTICULATE WING.

The articulate wing can be removed from the nut and can be replaced
without injury. An ineffective form of this wing is seen in the
Gerardianae and in P. pinea, where the blade is very short and the base
has no effective grasp on the nut.

The base of the effective articulate wing contains hygroscopic tissue
which acts with the h