BOOKS AND CURRENT LITERATURE 



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mountain, and an iJlustration is given of Agave growing at the summit at 

 8100 feet elevation. On the map of the state the summit of the Big 

 Hatchet Mountains is colored Transition. In other words it appears 

 that a zone is a zone even if all of its characteristic species are absent. 



It is earnestly to be hoped that the workers in the Biological Survey 

 will endeavor to develop a more natural system of zones, and that they 

 will depart frequently from their attempt to distinguish biogeographi- 

 cal regions on the basis of the controlling influence of a single environ- 

 mental factor. — F. S. 



