Spalding : Mechanical adjustment of suaharo 



63 



received a thorough wetting by overflow and subsequent leakage 

 from the water tank. It immediately stopped contracting, and in 

 the next few days all the furrows marked expanded from 



one 



(/^^ 



After the soil had dried the furrows ag; 



Nothing could show more clearly the relation between water- 

 supply and the expansion and contraction of the trunk of the giant 

 cactus than a comparison of the behavior of these artificially watered 

 plants and that of number i. Some idea of the limit of expan- 

 sion can be gained from number g, which after expanding for 

 about five weeks, remained nearly stationary for a month, though 

 the plant was well watered once a week. This would also indi- 



Jan. 



February 



March 



April 



Figure 4. Curves derived from measurements near the bases of different plants. 

 In this and the last two figures, in order to avoid confusion, the width of the furrows 

 was ignored in placing the curves on the metric paper; and the figures refer to the 

 number of the plant from which the curve was derived. Rain, February 6 (0.54 in.). 



cate that the expansion which took place was the result of the 

 absorption of water by the water-storing cells of the plant, and is 

 not to be referred to growth. 



The other suaharos that were measured — designated 6, 7, 10, 

 II, 12 — agree substantially with what has already been stated 



—numbered 5 and 8 — showed 



Two bisnagas 



regarding number i. 



I 



the same phenomena as the suaharos, but on a smaller scale. 



