Voi. 32 



No. 5 



BULLETIN 



OF THE 



TORREY BOTANICAL CLUB 



MAY, 1905 



Notes on the fruits of some species of Opuntia 



James William Toumey 

 (With plates 9 and 10) 



In the study of the species of Opuniia in the field, one is contin- 

 ually impressed by the correlation between structure and environ- 

 ment. The genus is, evidently, of comparatively recent origin and 

 development. As yet no one has been able to make a satisfactory 

 taxonomic disposition of the various species. This, evidently, is . 

 largely due to the instability of the characters which the system- 

 atist must use to separate the multiplicity of forms which comprise 

 the genus. 



A few species are known from humid regions. The genus as a 



whole is a desert type. Between 90 and 100 species and varieties 



have been described from the southwestern United States and 



northwestern Mexico, where they grow under the most arid con- 

 ditions. 



The correlation between the various organs of these plants and 

 the environmental conditions under which they have developed is 

 of great interest, not only to the morphologist but to tho student 

 of physiological botany as well. The fitting of form and structure 

 to function under a desert environment has resulted in the develop- 

 ment of organs along different lines and w^th different uses from 

 those of the homologous organs of plants of more humid regions. 

 In order to facilitate nutrition, dissemination, protection, and re- 

 production, under the adverse environmental conditions where the 

 plants grow, both structure and function are highly specialized. 



\ 



[The Bulletin for April (32 : 179-234) was issued 6 My 1905.] 



235 



