Acclimatization in Arizona. 15 



PLANT ACCLIMATIZATION IN SOUTHERN ARIZONA. 



J. J. Thornber. 



In a recent paper * on plants capable of successful cultiva- 

 tion in arid regions, the writer discussed briefly a list of native 

 and introduced species, including trees, shrubs and other plants, 

 which after several years of close observation have been found re- 

 markably well suited for growing in the drier parts of the South- 

 west. For reasons not always clear these plants have displayed 

 notably resistant qualities to all our extremes of climate, as well as 

 to our diverse soils. No matter how hardy plants may be as con- 

 cerns heat and cold, their failure to withstand other equally im- 

 portant factors, as aridity, means their inability to make healthy 

 or normal growth and ultimately their dying out. The posses- 

 sion of one or more hardy qualities for a plant is not sufflci'.-nt; 

 it must be strong in its make-up in every essential particular. 



A list of highly resistant plants like this must necessarily 

 be limited in our region, where the several factors controlling 

 plant growth are sufficiently pronounced and far-reaching in their 

 effects to render practically impossible the successful growing 

 of a verv large number of exotic species, even with good care. 

 LTpon examination it is not surprising to find that this list is 

 made up to a very considerable extent of native southwestern 

 plants, which, having become adapted by long-continued selec- 

 tion under adverse conditions, are manifestly able to flourish 

 under the same conditions with the added advantages resulting 

 from cultivation. 



Plants well suited to our climate, especially among exotics 

 long accustomed to growing under environments widely different 

 from our own, are indeed rare. In fact, only a relatively small 

 percentage of plants having a distribution limited to the cooler 

 or moister sections of the continent flourish in the more arid and 

 heated parts of the Southwest. The failure of such species as 

 these to thrive here, except perchance at the higher altitudes, is 

 scarcelv to be wondered at. On the other hand, it is to be 

 noticed with great interest that a very considerable percentage 



*Thomber, J. J. Drought-Resistant Plants for the Arid Southwest. Timely Hints for 

 Farmers. No. 83. Ariz. Exp. Sta. Jan. 1910. 



