62 



Spalding : Mechanical adjustment of suaharo 



three weeks, number 2 remained practically stationary. After 

 this, two of three furrows that were marked shrank ; but it was 

 now receiving very little water. 



The correlation of the expansion and contraction of the stem 

 with its water-supply is demonstrated still more clearly by the 

 measurements of another individual designated as number 9. On 

 February 15, when the cacti under observation w^ere all in process 

 of expansion, this plant was selected and watered in order to 

 ascertain whether by this means the period of expansion could be 

 prolonged. Until March 4 it was given 8 to 12 gallons of water 

 three times a week; after that, it was watered once a week until 



February 



March 



April 



May 



2:2 



M— « s* c* T* ;* ffi f 



'IT 



1:61 



1:56 



1:5X 



1:46 



1:41 



1:36 



1:31 



1:26 



1:21 



1:16 



1:11 



1:6 



FiGUUE 3, Representative 

 ber 9. The lowest curve represents the variations in the thickness of a rib. 



num- 



April 



with alkaline salts. 



The water used was the ordinary tap-water charged 



/. 



expanded very rapidly until about March ii, from 



weeks after the other cacti had begun to contract. 



until between April 9 and 13 the furrows remained 



same width while those of the others, except number 2, were^^con- 



tracting, some of them quite rapidly. 



During this time, however, one cactus, number a. accidentally 



From then 

 about the 



