24 



THE WATER-BALANCE OF SUCCULENT PLANTS. 



remains soaked for weeks. Moreover, each plant seems to have a very 

 definite Hmit beyond which it will not expand, no matter how much water 

 it can gfet. 



Fig. 12. — Curves from measurements of three intervals on sahuaro No. i and 

 one curve (o) showing combined variation of the three others. Effects of 

 watering. November 28, 1908, to May 14, 1909. 



During the winter of 1904-05 the ground was wet much of the time from 

 January 1 to April 15. If at any time between these dates a sahuaro 

 which had been deprived of water for some time had been transferred into 

 this soil, it probably would have absorbed water and expanded rapidly. 

 But the sahuaros which were already in the ground, while they responded 

 promptly to the first rains, showed little or no expansion thereafter until 

 the warm weather in May. In the following winters, 1905-06 and 1906-07, 

 though less rain fell, the intervals reached practically the same size. But 

 in the winters of 1903-04 and 1908-09 there was so little rain that the 

 ground was not saturated long enough at any time for the intervals to 

 reach their maximum expansion. These statements will be evident from 

 table 5, which shows the greatest expansion attained by the three marked 

 furrows of No. 1 for several years. 



