BOTANICAL LABORATORY IN THE DESERT. 331 



to the westward are to be seen the outposts of the Tucson Mountains, 

 rugged hills of volcanic origin. On the more gradual northerly face of 

 one of these, on a shoulder of gentle slope, stands the laboratory, a build- 

 ing appropriately constructed of the volcanic rock. The style is simple 

 and well adapted to the climate. The thick stone walls heat slowly, 

 particularly as they are for the most part protected from the direct rays 

 of the sunlight by an overhanging roof. This latter is so constructed 

 as to form a large ventilated air chamber, itself a protection from 

 the effect of intense insolation as well as affording comfort to the 

 occupants by modifying the strong light. 



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The form of the building is in the shape of the letter L, with the 

 longer outer elevation facing the north. The dimension and disposi- 

 tion of the space within are indicated upon the accompanying plan. 

 The windows are abundant, and when open to the brisk winds 

 allow a current of air throughout the building which makes one for- 

 get the heat. About this factor much misapprehension is abroad. To 

 be sure, the mercury stands high, and a registration of 100-105° F. is 

 not at all unusual; occasionally it is even higher, and doubtless if one 

 did not forget to look at the instrument, still higher temperature could 

 be discovered. Fortunately, this is just what one does. There is so 

 little discomfort attendant upon the heat that it is usually quite dis- 

 regarded, a condition happily due to the low relative humidity, which 

 on many occasions during six weeks in July and August of this year 

 ran down as low as 7 per cent. The only feature of discomfort to some 

 persons is the intense illumination, and one may require dark glasses, 

 .although I personally found no discomfort even upon the mesa. On 



