SEASONS IN SOUTHERN ARIZONA 



229 



O. fitlgida is characterized by the silvery, shiny appear- 

 ance of the sheaths of the spines, and is locally known as 

 "cholla" although that name properly belongs to a species 

 native to Baja California, much further south. Nearly 

 related to O. fiilgida and growing intermingled with it is O. 

 mamilJata, with more greenish branches and shorter and 



Fig. 11. Upuntia ai-ijusciiiH. 



sparser spines. Both species have easily detachable branches, 

 and the separated portions act as cuttings in propagation. The 

 facility with which the joints are cast loose and attach them- 

 selves to an animal by the sharp spines makes them much to 

 be dreaded, and it is by this means that dissemination is effect- 

 ed in a very efficient manner. The fruits remain attached to 

 the branches for several years, and the seeds are exceedingly 

 slow of germination. 



