20 GENUS PINUS 



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 indurated oblique cone with an elaborate form of winged seed and an intermit- 

 tent dissemination, appears among the species in various degrees of development as follows — 



The seed 



1. wingless. 



2. with a rudimentary wing. 



3. with an effective adnate wing. 



4. with an ineffective articulate wing. 



5. with an effective articulate wing. 



6. with an articulate wing, thickened at the base of the blade. 



The cone 



1. indehiscent. 



2. dehiscent and deciduous. 



3. dehiscent and persistent. 



4. persistent and serotinous. 



and as to its form 



5. symmetrical. 



6. subsymmetrical. 



7. 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. 



SPECIFIC CHARACTERS 



All aspects of vegetative and reproductive organs may contribute toward a determination of 

 species, but the importance of each character is often relative, being conclusive with one group of 

 species, useless with another. Characters considered by earlier authors to be invariable with species, 

 such as the dimensions of leaf or cone, the number of leaves in the fascicle, the position of the resin- 

 ducts, the presence of pruinose branchlets, etc., prove to be inconstant in some species. In fact, as 

 the botanical horizon enlarges, the varietal limits of the species broaden and many restrictions 

 imposed by earlier systems are gradually disappearing. 



