-scales, and then the distinction between the upper and lower parts
of the trunk becomes lost.

[Illustration: PLATE VII. THE WOOD]

SUMMARY

The various characters that have been considered in the previous pages
may be classified under different heads, some of them applicable to the
whole genus, others to larger or smaller groups of species.

GENERIC CHARACTERS

Several characters, quite distinct from those of other genera, are
common to all the species.

1. The primary leaf--appearing as a scale or bract throughout the
life of the tree.
2. The bud--its constant position at the nodes.
3. The internode--its three distinct divisions.
4. The secondary leaves--in cylindrical fascicles with a basal
sheath.
5. The pistillate flower--its constant nodal position and its
verticillate clusters.
6. The staminate flower--its constant basal position on the
internode and its compact clusters.
7. The cone--its clearly defined annual growths.

Pinus is also peculiar in the dimorphism of shoots and leaves and in
their constant interrelations with the diclinous flowers. Evolutionary
processes develop features peculiar to Pinus alone (the oblique cone,
etc.), but confined to a limited number of species.

SECTIONAL CHARACTERS

There are several characters that actually or potentially divide the
genus into two distinct sections, popularly known as Soft and Hard
Pines.

1. The fibro-vascular bundle of the leaf, single or double.
2. The base of the bract subtending the leaf-fascicle, non-decurrent
or decurrent
3. The phyllotaxis of the cone, simple or complex.
4. The flower-bud, its less or greater development.

Some characters indicate the same distinction but are subject each to a
few exceptions.

5. The fascicle-sheath, deciduous or persistent.
6. The walls of the ray-tracheids, smooth or dentate.
7. The connective of the pollen-sacs, large or small.
8. The formation of bark, late or early.

SUBSECTIONAL CHARACTERS

An exact subdivision of the Soft Pines is possible on the following
characters.

1. The umbo of the cone-scales, terminal or dorsal.
2. The scales of the conelet, mutic or armed.
3. The pits of the ray-cells, large or small.

EVOLUTIONAL CHARACTERS

The progressive evolution of the fruit of Pinus, from a symmetrical cone
of weak tissues, bearing a wingless seed, to an indura