noo 



EDITH BELLAMY SHREVE 



tion which took place during the intervals between measurements 

 are given, in centimeters, in table 1, the plus sign being used to 

 denote an upward movement and the minus, a downward one. 

 The general appearance of the plants under the several con- 

 ditions is indicated by the diagrams in figure 1. These show 

 only the extreme positions assumed in wet and in dry soil. The 

 downward movement took place gradual^, occupying weeks 

 or months, while the upward movement was rapid after rain 

 or irrigation and occupied only a few days. 



A 



Oct. 2 Oct. 17 Oct22 



Oct.22 Dcc.2 Mar 20 



^3 



Oct.22 Jan.21 Mar.20 



Oct 22 



Dec 2 



Mar. 20 



Fig. 1. Diagrams to illustrate the relations of movements of Opuntia versi- 

 color to the water-content of the soil. For details see table 1. 



The second set of observations was made by means of measure- 

 ments and by securing series of photographs. Negatives were 

 made of five adult plants, growing in the open, at successive 

 seasonal periods of wet, dry, and wet soil, the camera being 

 accurately placed in the same position each time. All five of 

 the plants showed similar behavior. In figure 2 appear views 

 of the smallest plant of the series. 



Both of the above sets of observations show that when the 

 positions are noted at the same time each day, they change with 

 the amount of water in the soil, a low position being assumed 



