VARIATIONS OF THE WATER-BALANCE. 



71 



A number of other tubers were brought in and set up in the laboratory 

 during April, 1910, for the continuation of the endurance tests, and the 

 results of the observations justify the assumption that the record of the 

 plant given above represents the average behavior of the species. A com- 

 parison with Echinocadus shows that a small plant of the latter reduced to 

 a weight of 530 grams by desiccation for 26 months lost 6 grams of water 

 during the 30 days ending April 21, while an Ibervillea weighing 510 

 grams freshly taken from the soil was depleted of only 2 grams in this 

 period. The Echinocadus lost 14 grams during the next 22 days, while 

 the Ibervillea decreased but 4 grams. 



This comparison illustrates the obvious conclusion that indurated tubers 

 and woody stems are much more efficient as storage organs than the green, 

 soft bodies of the cacti and other succulents. 



