DESEET PLANTS AS A SOURCE OF DRINKING WATER. 503 



was a tin box 10 by 20 b}^ li inches, open at the top, but with a thick 

 la3'er of earth at the bottom. Doctor Allen summarized his experience 

 with the animal in the statement, ''As no water and no fresh vegeta- 

 tion have been given him for nearly three years, it is evident that the 

 only moisture required for his sustenance is derived wholly from dry 

 birdseed."' A water content determination of dry mixed birdseed, 

 made in Washington, December 31, 1903, shows 11.75 per cent of 

 moisture. Freshly matured wheat grains in the climate of the arid 

 portions of California have a water content of only 6 to 8 per cent of 

 their weight. It is impossible that these rodents, performing their 

 functions of respiration, digestion, and secretion, can subsist on this- 

 amount of moisture. The subject is one that deserves precise quanti- 

 tative measurement as well as anatomical investigation. Is it possible 

 that these animals possess some apparatus by means of which they can 

 abstract moisture from the air h3'groscopically and condense it for 

 their own use i Or do they manufacture the water they require by the 

 chemical dissolution of starch? 



However this may be, it is clear from some of the cases cited that 

 the water suppl}^ of many desert animals, either for long periods or 

 during their whole lives, comes not from natural water, but from that 

 stored in the tissues of plants. It is an old established fact that ani- 

 mals do not possess the power to manufacture their food out of the 

 raw mineral constituents of the soil, but that these constituents must 

 first be elaborated into starch or other food products by plants. To 

 this fundamental dependence of animal upon vegetable life may be 

 added, in the case of many desert animals, their further complete 

 dependence on plants for their supply of water. 



Under certain conditions this dependence of desert animals upon 

 plants for their water is extended even to the human race. The rain- 

 fall of the desert of Sonora is so small and so irregularly timed that 

 periods of prolonged drouth occur, during which man}^ of the cus- 

 tomary sources of water supply, always few and far between, fail 

 utterly. To two of the native tribes, the Seris and Papagos, such a 

 condition is not necessarily serious, for they betake themselves to the 

 water stored in cactuses. 



Some of the largest cactuses, such as the saguaro, or giant cactus 

 ( Oereus giganteus), the pitahaya ( Oereus tkurberi), and the sina {Pilo- 

 cereus schottil)^ are not availa})le as a source of drinking water, for 

 their juice is bitter and nauseating. But the juice of certain species 

 of the genus Echinocactus, notably E. emoryi and E. loislizeni^ is sweet 

 and palatable. These cactuses, the Mexican name of which is bisnaga, 

 are known b\' all natives of the desert region as a potential source of 

 drinking water. In February, 1903, the writer, in company with Dr. 

 D. T. MacDougal, while seeking a location for a desert botanical labo- 

 ratory for the Carnegie Institution, found an opportunity to observe 



SM 1903 33 



