GENUS PINUS 23 



The second group, the Australes, contains species with small ray-pits, cones dehiscent at maturity 

 and spring-shoots gradually changing, among the species, from a uninodal to a multinodal form. 

 They are, without exception, species of the New World. 



The third group, the Insignes, contains the serotinous species. The ray-pits are small and the 

 spring-shoots are, with two exceptions, multinodal. With two exceptions, P. halepensis and 

 P. pinaster, they are New World species. 



These three groups, being the progressive sequence of a lineal evolution, are not absolutely cir- 

 cumscribed, but are more or less connected through a few intermediate species of each group. The 

 systematic position of these intermediate species is determined by their obvious affinities. It can- 

 not be expected that the variations, which take an important part in the evolution of the species, 

 progress with equal step or in perfect correlation with each other. 



As to specific determinations, a little experience in the field discloses an amount of variation in 

 species that does not always appear in the descriptions of authors; and species that are under the 

 closest scrutiny of botanists, foresters or horticulturalists, attest by their multiple synonymy their 

 wide variation. The possibilities of variation are indefinite and, with adaptable Pines, the range of 

 variation is somewhat proportionate to change of climate. In mountainous countries, where there 

 are warm sheltered valleys with rich soil below cold barren ledges, the most variable Pines are found. 

 The western species of North America, for instance, are much more variable than the eastern spe- 

 cies, while in Mexico, a tropical country with snow-capped mountains, the variation is greatest. 



Therefore in the limitation of species undue importance should not be given to characters respon- 

 sive to environment, such as the dimensions of leaf or cone, the number of leaves in the fascicle, etc. 

 Moreover, there are familiar examples (P. sylvestris, etc.) that show the possibility of wide differ- 

 ences in the cone of the same species. 



In the following classification species only are considered without attempting to determine varietal 

 or other subspecific forms. But varieties are often mentioned as one of the factors illustrating the 

 scope of species. Synonymy serves a like purpose, but synonyms not conveying useful information 

 are omitted, Roezl's list of Mexican species, for instance, and variations in the orthography of spe- 

 cific names. 



