DESERT PLANTS AS A SOURCE OF DRINKING WATER. 505 



protected against the depreciations of animals by its bitter and poison- 

 ous juice. 



Anotlier notable feature in the mechanical construction of the bis- 

 nao-a is the fluted character of its surface. Between the times when 

 its body is fully distended with water from the absorption following- 

 a heavy rain and other times when its interior tissues are far shrunken 

 after a prolonged drought, the plant, if ordinarily constructed, would 

 be ver}' liable, from the repeated wrinkling and stretching of its hard 

 skin, to injury by cracking. What form could be more admirably 

 suited to accommodate the bisnaga to this feature of its existence than 

 the fluting of its surface, each fluting or rib becoming thick by the 

 absorption of water and thin by its loss i 



Streiuious are the conditions to which the plants of the desert are 

 doomed; many and remarkable are the devices with which these con- 

 ditions are met, and rich are the opportunities for research where 

 such phenomena exist. It is a matter for congratulation that to the 

 United States belongs the credit of first establishing a botanical labo- 

 ratory in the midst of the desert. Such a laboratory has been founded 

 near Tucson, Arizona, by the Carnegie Institution of Washington, 

 and we may contidently expect to learn from time to time of results 

 which shall excite our wonder and which shall constitute new contri- 

 butions to the sum of human knowledge. 



