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THE AMEBIC AX NATURALIST [Vol. XLI1I 



For all these habitats the fact is to be emphasized that 

 the general climatic conditions are the same, and it is 

 important to note that not a few of the plants which grow 

 where a sufficient or even abundant water supply is as- 

 sured are nevertheless marked, as a rule, as plants of 

 an arid region by their coriaceous, hairy or otherwise 

 xerophilous leaf structure. The point to be specially 

 noted here is that while plants of the arid, or semi-arid 

 southwest grow in a great variety of habitats, some of 

 which are by no means dry, all are subject to the severe 

 conditions of a desert climate, especially intense insola- 

 tion, low percentage of atmospheric moisture, and drying 

 winds. The problem, therefore, of the occupation of any 

 one of these habitats is successfully met only by those 

 plants that are already adapted, or are capable of indi- 

 vidual adjustment to the dry air and hot sun in which 

 they must live ; all others inevitably fail. 



This will be made clear by reference to the introduc- 

 tion, or attempted introduction, of various cultivated 

 plants, a subject which presents a most instructive his- 

 tory. The yards of Arizona cities constitute an experi- 

 ment station in which year by year, at private instead 

 of public expense, the availability of one species after 

 another for desert planting is being determined. From 

 the great number of plants successfully cultivated there 

 seems, at first sight, to be sufficient justification for the 

 reiterated assertion that anything will grow here if you 

 only give it water enough, but closer attention to the 

 actual facts of the case makes it evident that this state- 

 ment is true only in part, and that there are many plants 

 that will grow only indifferently or not at all under the 

 atmospheric conditions which prevail here, especially in 

 the summer time. To give a few examples, geraniums, 

 the universal easily raised plants of moister regions, are 

 very uncertain, some varieties accommodating themselves 

 fairly well to the desert air, while others fail altogether. 

 Cannas and gladioli, which grow side by side in the east, 

 part company here, the former making a good growth in 



