52 ERYTHEA. 



NOTES UPON SOME RARE WYOMING PLANTS. 

 By Aven Nelson. 



A plant's range or geographical bounds may be extended or 

 restricted accordingly as one draws the characters of the species 

 loosely or rigidly. We now frequently see so-called " polymorphous n 

 species, of wide geographical range, broken up into well-defined 

 forms of greatly restricted range. This process of segregation be- 

 comes possible only after extended field-work^ and the accumulation 

 of large series of specimens of the several forms, in order that the 

 fairly constant characters may be the more surely made out. Most 

 of the plants in the following list extend the supposed range of the 

 species, but, as has so often occurred in the past, a completer knowl- 

 edge of the different forms may show that what now seems to be 

 only such slight differences as environment might produce are good 

 diagnostic characters. It is no easy matter to determine the relative 

 importance of the factors that govern the range of a species. 

 Miles and mountain ranges seem, to me, less important than soil 

 conditions. But with the same sojl conditions, how far must varia- 

 tion in size, branching, surface (hirsuteness, etc.), color of flowers 

 and other characters due to climate, or other conditions, proceed 

 before the plants may be considered specifically distinct? Upon 

 one's answer to this question largely depends the disposition that will 

 be made of certain material. 



The notes upon the following plants maybe of interest as indicat- 

 ing ( how largely soih- conditions are responsible for similar, if not 

 identical, forms in widely separated localities. Most of the plants 

 are from the Red Desert of Wyoming, certain localities of which 

 are no doubt the counterpart of the type-localities of at least some 

 of the species here listed. 



Streptanthus longirostris Watson. Seemingly typical speci- 

 mens of this were secured in sandy, alkaline soil at Green River 

 (3,040), and at Point of Rocks (3,082), thus extending the range 

 eastward to south-central Wyoming.* 



* Unless otherwise stated, all are from my collections of 1897. 



