EVOLUTIONAL CHARACTERS
The progressive evolution of the fruit of Pinus, from a symmetrical cone of weak tissues, bearing a wingless seed, to an indurated oblique cone with an elaborate form of winged seed and an intermittent dissemination, appears among the species in various degrees of development as follows—
The seed
- wingless.
- with a rudimentary wing.
- with an effective adnate wing.
- with an ineffective articulate wing.
- with an effective articulate wing.
- with an articulate wing, thickened at the base of the blade.
The cone
- indehiscent.
- dehiscent and deciduous.
- dehiscent and persistent.
- persistent and serotinous.
and as to its form
- symmetrical.
- subsymmetrical.
- oblique.
These different forms of the seed and, to some extent, of the cone, are available for segregating the species into groups of closely related members; while the gradual progression of the fruit, from a primitive to a highly specialized form of cone and method of dissemination, points to a veritable taxonomic evolution which is here utilized as the fundamental motive of the systematic classification of the species.