GENUS PINUS 21 



Variation is the preliminary step toward the creation of species, which come into being with the 

 elimination of intermediate forms. Variation in a species may be the result of its participation in 

 the evolutionary processes culminating in the serotinous Pines, or it may result from the ability 

 of the species to adapt itself to various environments by sympathetic modifications of growth, or 

 it may arise from some peculiarity of the individual tree. 



Evolutionary variation is associated with the gradual appearance of the persistent, the oblique 

 and the serotinous cone, and of the multinodal spring-shoot. For these conditions appear in less or 

 greater prevalence among the species of the genus. 



Variation induced by environment finds familiar illustrations among the species that can survive 

 at the limits of vegetation and can meet these inhospitable conditions by a radical change of all grow- 

 ing parts. Such variations are mainly of dimensions, but, with some species, the number of fascicle- 

 leaves is affected and the shorter growing-season may modify the cone-tissues. In Mexico and 

 Central America are found extremes of climate within small areas and easily within the range of dis- 

 semination from a single tree. The cause of the bewildering host of varietal forms, connecting widely 

 contrasted extremes, seems to lie in the facile adaptibility of those Pines, which are able to spread 

 from the tropical base of a mountain to a less or greater distance toward its snow-capped summit. 



The peculiarities of individual trees that induce abnormally short or long growths, the dwarf or 

 other monstrous forms, the variegations in leaf-coloring, etc., etc., are not available for classification, 

 for they may appear in any species, in fact in any genus of Conifers. These variations are artificially 

 multiplied for commercial and decorative purposes. But inasmuch as they are repeated in all species 

 and genera of the Coniferae that have been long under the observation of skillful gardeners, their 

 significance has a broader scope than that imposed by the study of a single genus. 



