304 MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 



temperature was then brought down to 25° C. and after twelve hours 

 at this point it showed rates of 5.4 mm., 6.6 mm., 6.6 mm. and 5.4 

 mm, daily for two days as measured at two hour intervals. The 

 temperature was now raised to 35° C. at which the rate was 16.4 

 mm. to 16.8 mm. daily for an entire day. This rate was fairly 

 duplicated on a second day, but with a somewhat wider variation, 

 the rate ranging from 15.6 mm. daily to 22.2 mm. daily (Fig. 2). 

 The etiolated shoot of a second Opuntia elongated as follows : 



Rate of I mm. daily at 19° C. 



Rate of 1.3 mm. daily at 19° C. 



Rate of .7 mm. daily at 15° C. 



Rate of .93 mm. daily at 15-18° C. 



Rate of 1.08 mm. daily at 17-18° C. 



Rate of 1.44 mm. daily at 18-19.5° C. 



Rates of I, 2, 1.2, 1. 1 5, .85 and i mm. per day at 16-18° C. 

 The preparation was moved into control chamber and the follow- 

 ing results were obtained: 



Rates of 2.9, 3, 3, and 3 mm. daily at 26° C. 



Rates of 3.2 and 3.44 mm. daily at 26° C. 



Rate of 4.2 mm. daily at 29° C. 



Rates of 3.6, 6.7 and 9.6 mm. daily at 30° C. 



Rates of 11.4, 11.4, 8.4, 9.2, and 11.4 mm. daily at 31.5-32° C. 



The heat was now cut ofif and rates of 4 mm. daily at 17° C. were 



displayed. 

 Rate of 5.7 mm. daily at 18.5° C. 

 Rate of 5.3 mm. daily at 19° C. 



The temperature being raised again from 18° C. at 8 A.M. to 

 39° C. at 12 130 midday, a rate of 8.4 mm. daily was displayed during 

 the first hour. 



The continuation of similar temperatures during two days was 

 attended by sustained rate of 18.6 to 19.2 mm. daily (37-38° C). 

 After three days at this temperature it was raised from 37° C. to 

 45° C. in 1.5 hours during which time the elongation was at the rate 

 of 13.2 mm. daily, and growth stopped entirely at 45° C. Some 

 shortening now ensued, but at the end of an hour and a half elonga- 

 tion began again at 46° C, and was maintained at the rate of 25 

 mm. per day for an hour, and the total for the four succeeding hours 

 at 46° C. was a rate of about 20 mm. daily, which was not exceeded 

 by any rate at lower temperatures. The rate during the sixth hour 



