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THE POPULAR SCIENCE MONTHLY. 



A CHARACTERISTIC SOUTHWESTERN PLANT GROUP. 



BY HENRY L. CLARKE. 



A CURIOUS fascination gathers round any type of plant life 

 that stands alone, as peculiarly characteristic of some one 

 region of the world ; and still greater does the interest become 

 when we find, instead of a single type, an extensive group of 

 closely related types holding a thus isolated position, and consti- 

 tuting a flora of themselves apart from surrounding plant realms. 

 But such instances are rare their very fewness primarily accounts 

 for the impression they make upon both scientist and general 



FIG. 1. OPUNTIA, CEKEUS, AND YUCCAS. 



observer. In one corner or another of every continent botanists 

 have found oddly specialized floras, distinct in aspect and purpose 

 from the general run of vegetable forms. Many of these cases 

 are of insignificant importance, save in their immediate interest 

 to the specialist ; some attract greater attention, as filling an espe- 

 cially noticeable gap in the series of plant relationships ; a few 

 become of widespread interest not only through unique special- 

 ization of structure, but also by virtue of their holding a really 





