38 



THE WATER-BALANCE OF SUCCULENT PLANTS. 



was first seen on March 11 and by March 29 twenty-three buds were devel- 

 oped on five of the six joints measured, two of which formed joints and 

 four remained undeveloped. By April 29 six had flowered and the rest 

 were nearly ready to do so (fig. 16). 



On No. 3 {Opuntia discata) eight terminal joints on different parts of 

 the plant were measured, each in one place. Budding was first seen on 

 March 18, and by March 29 each of the eight joints was bearing from 1 

 to 13 buds, 55 in all, 3 of which failed to develop. 



On No. 4 iOpuntia sp.) six joints were measured, each in one place. 

 These six joints formed a series, of which 1 was the oldest and lowest and 

 6 the terminal joint. On March 11 a bud was seen on the second joint, 

 followed on March 18 by one each on the fourth and sixth. By April 29 

 the three were nearly full-grown. 



South 



Fig. 16. — Curves from measurements of six Opuntia segments of plant No. 2, 

 three on north and three on south. X shows date when buds were first seen. 

 November 3, 1906, to May 25, 1907. 



In constructing the curves from the measurements of Opuntia each ver- 

 tical space represents 0.01 inch and each horizontal space 1 day. 



It was perfectly plain that the joints increased in thickness under the 

 influence of added water in the soil. In fact, this needed no demonstra- 

 tion, for the contrast between the thin, wrinkled segments at the end of a 

 long dry period and the same parts, smooth and well filled out after a rain, 



