50 THE WATER-BALANCE OF SUCCULENT PLANTS. 



ECHINOCACTUS. 



The short stems and relatively enormous thickness of the echinocacti, 

 together with the curved or hooked spines and amount of accumulated 

 water which they contain, has caused them to be designated by a number 

 of local names, such as "barrel cactus," "bisnaga," "desert fountain," 

 etc. One or more of the South American species, together with E. emoryii 

 and E. wisliseni, hold so much water, which is readily yielded upon crush- 

 ing, that the sap is used as an emergency drink by the aboriginal tribes of 

 both North and South America. The great body of the Sonoran species 

 named has a very thin central woody cylinder, occupying but little of the 

 space within the plant, which is chiefly composed of a soft parenchymatous 

 tissue with fragile strands of fibrovascular tissue running out to the nodal 

 points. (See Coville and MacDougal, Desert Botanical Laboratory, Car- 

 negie Institution of Washington Publication No. 6, 1903; also MacDougal, 

 Carnegie Institution of Washington Publication No. 99, (1908.) The ex- 

 pressed juice is found to contain less dissolved material than that of any 

 other plant examined. 



The contents of these watery cylinders are easily available to the thirsty 

 traveler. A large knife is convenient for decapitating the plant, but when 

 this is lacking the large curved spines may be burned away by a lighted 

 match or wand, and then the top crushed with a stone. Singularly enough, 

 the apical newer tissues do not yield their juices as readily as the older 

 parts, being leathery and retentive of the sap. Aiter this is removed the 

 underlying parenchyma may be crushed by pounding with a stake or stone 

 and the juice squeezed into the cavity from which the tissues were re- 

 moved. A liter of refreshing fluid may be obtained by a skillful operator 

 in a few minutes, and the rigors of thirst on many desert journeys have 

 been mitigated by its means. (Coville, F. V., Desert Plants as a Source 

 of Drinking- Water, Smithsonian Report for 1903, p. 499, 1904.) 



A large number of specimens of Echinocadus have been seen in a prostrate 

 position on various explorations within the last five years. The root-system, 

 while very extensive, lies within 15 cm. of the surface of the soil, and a 

 slight dislocation due to the action of a torrential rain may loosen the an- 

 chorage of a large individual in a few minutes. Here, again, no exact ob- 

 servation may be reported, but many have given evidence of survival for 

 long periods after being freed from absorbent contact with the soil. No 

 instances have been reported in which new roots were seen to arise from 

 the lateral points of a prostrate trunk, although when the apical portion is 

 destroyed regeneration may occur by which several heads or branches are 

 formed, while fasciations or "cri stations," probably due to injury, are by 

 no means uncommon in the two species specially studied. Widely vary- 

 ing experimental observations were designed to test the water-relations of 

 these forms, and the results are described below. 



