TORREYA 



Vol. II 



June, igii 



No. 6 



A NOMENCLATORIAL PROBLEM WITH A DESCRIP- 

 TION OF A NEW FORM, PETALOSTEMUM 

 PURPUREUM F. ARENARIUM* 



By Frank C. Gates 



Individual plants of a given species occupying different habitats 

 may become considerably modified, giving rise to variation among 

 themselves. This is usually conceded to be an adaptation, 

 induced by the local habitat, in the individual plant. To a 

 taxonomist, the resulting form is but an extreme variation from 

 the type and no general advantage is secured in giving it a name. 

 A specific name is inapplicable, as complete series of inter- 

 grading forms are frequently present. To an ecologist, however, 

 the matter stands in a very different light. He is dealing primarily 

 with plants in their habitats. The ability of a single species to 

 live in more than one habitat may often be an important factor 

 in determining the relationships of the vegetation. 



The usual form of a species tends to grow in the preferred 

 habitat of that species. Widely varying forms are likely to be 

 results of associational succession. The forms are consequently 

 given the terms relics or invaders according to their position in 

 the genetic series of succession. The form of the relic species 

 changes because some of the external conditions have been 

 changed by the successful invasion of an association. The 

 invasion of the forest upon the prairie furnishes many excellent 

 examples through the persistence of a number of prairie species 



* Contributions from the Botanical Laboratories of the University of Michigan 

 No. 124. 



Submitted with the spelling in accordance with recommendations of the Simpli- 

 fied Spelling Board, and changed to conform to the editorial policy of Torreya- 

 — N. T. 

 (No. 5, Vol. II, of Torreya, comprising pp. 101-124, was issued 17 May 1911] 



125 



