1903.J NATURAL SCIENCES OF PHILADELPHIA. 659 



In the higher terrestrial vertebrates, as ah'ead}' pointed out, the 

 ranges of several closely related forms are coextensive with the limits of 

 the several life-areas to the peculiar environmental conditions of 

 which they owe their origin. Consequenth' we never find two geo- 

 graphic races or subspecies of the same form occurring together, 

 except during times of migration. Among reptiles, however, we do- 

 find variants of the same form which have been generally rated as 

 subspecies occurring in the same life-area. We perhaps need more 

 material and more exact data regarding habitat, etc., before the proper 

 status of such forms is established. They may be color types or 

 dimorphic forms produced indiscriminately throughout the range of 

 the species; or are, perhaps, due to local, soil or other conditions 

 prevailing in different areas within the range of the species. The fact 

 that such forms occur together and intergrade, however, seems abun- 

 dantly proven. 



The above resume is presented, showing the conditions which exist 

 among terrestrial vertebrates with regard to racial variation, in order 

 that they may be compared with the conditions that prevail among 

 plants. 



Racial Variation Among Plants. 



As is well known, the trees and shrubs, as well as other plants in a less 

 degree, conform with more or less exactness to the same general 

 laws of geographic distribution that pertain to animals; and the ranges 

 of many species are limited by the life-zones that have been established 

 originally from a study of birds and mammals. 



When, however, a genus is represented by different forms in several 

 life-zones, they are usually very distinct species and not closely related 

 variants which have obviously been differentiated from a connnon 

 parent type by prevailing environmental conditions in the several 

 life-areas in question, such as is so frequently seen among vertebrates. 



At the same time an abundance of closely related variants do exist 

 among plants, differentiated to the same varying extent as in the geo- 

 graphic races of birds and mammals, but all occurring in the same life- 

 zone or area, and often side by side. They are, moreover, quite con- 

 stant in their racial characters, and certainly not cases of individual 

 variation. 



Obviously some other agency must be responsible for this differenti- 

 ation, and it is in many cases no doubt to be found in the varying 

 soil conditions, and in other local peculiarities not sufficiently potent 

 to affect higher animal life. Owing to the fixed nature of plant life. 



