DESERT PLANTS AS A SOURCE OF DRINKING WATER. 



501 



areas which permit the ready transfer of water from one cell to 

 another throughout the interior. Doctor ]McKenney has made a 

 determination of the water in a sam- 

 ple of this storage tissue and finds 

 the astonishing amount, by weight, 

 of 96.3 per cent. The plant when 

 mied to its capacity is almost a tank 

 of water. 



That animals which live in a desert 

 would have difficulty in securing a 

 regular supph' of water is evident. 

 But it is a matter of fact that many 

 of these animals go without water 

 for months at a time, deriving all 

 their moisture from the watery tis- 

 sues of plants; and there is conclusive 

 evidence that some animals never 

 drink water, apparently not knowing 

 what water is, and never eat even 

 ordinary herbage, but subsist on dry 

 seeds alone. D. W. Carnegie records 

 the statement" that while traveling 

 across the desert of southwestern 



Australia, his band of 9 camels went ^''^- 3.-Tran.spiration pore of Echinocactus 

 , emoryi. a, Epidermis; 6, outer wall of epi- 



Wlthout water from July 29 to August dermal cell; c, cuticle; d, cavity of epidermal 

 10, 1896, a ])eriod of twelve daVS, on ^^11; e, hypodermis; /, green interior tissue; 

 '■ • II ' 1 • 1 fi'' giii'^rd t'ells of the transpiration pore; h, 



the latter date taking a full drmk transpiration chamber. Much enlarged. 



averaging 1 7 gallons each ; while i> of ^"*^' McKenney. 



his camels performed a still more wonderful feat of abstinence in 



traveling for a period of thirty-seven 

 days, from August 22 to September 

 28, 1896, on only 18 gallons of water 

 each, which they drank as follows: 

 August 29, after seven days, 2 gal- 

 lons; September 8, after ten days 

 more, 8 gallons; September 18, after 

 an additional ten days, 3 gallons. 

 Bands of Merino sheep grazing on 

 the tender annual vegetation that 

 springs up on the desert near Phoe- 

 nix, Arizona, after the winter rains, 



Fig. 4.-Water storage tissue of Echinocactus sometimes drink UO WatCr for a pC- 

 emoryi. a, Water-storage cells; b, intercelln- . , , , . , ~^ . 



lar spaces; p, sieve plates, face view; d, sieve riod of forty to SlXty daVS. In the 



plates, in cross section. After McKenney. dcSCrt plain of SoUOra, MexicO, WCSt 



of the railroad station of Torres, are isolated rocky hills in which 



«D. W. Carnegie, Spinifex and Sand, pp. 19-4, 261. 1898. 



