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.

1. Umbo terminal Subsection Cembra fig. 46-a.
2. Umbo dorsal Subsection Paracembra fig. 46-b.

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 t