MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 305 



rose to 20.4 mm. daily at 45° C. The temperature being raised to 

 49° C. during the next hour, elongation ensued at the rate of 18.7 mm. 

 daily until it was checked at 48.5° C. The period of checking was 

 not measured accurately, but after an hour with the temperature still 

 between 48° C. to 46° C. the rate was 19.2 mm. daily. It is thus 

 to be seen that the maximum is maintained up to very near the point 

 of actual cessation of growth, an experience duplicated scores of 

 times with green plants in the glass house at Tucson. It was noted 

 that the air temperature was 40° C. and 41° C. when the plant was 

 at its maximum of 48° C. and 49° C. Similar differences have 

 probably gone unnoted in the observations made by many workers. 



After the experiences described above the plant remained at 

 45° C. and 46° C. over night without calibration. Measurements 

 begun at 7 130 A.M. at 45° C. Elongation during the hour and a 

 half in which the temperature rose a degree and a half (to 47.5° C.) 

 amounted to .95 mm. at a rate of about 15 mm. daily. Continued 

 rise of temperature was accompanied by lessened growth which 

 did not cease altogether until 49° C. was reached. Elongation was 

 resumed at this temperature however after 20 minutes, but was 

 checked again. The temperature was now raised to 52° C. for a 

 half hour with an air temperature of 43° C. Reducing the tempera- 

 ture to 49° C. with an air temperature of 41° C. resulted in a growth 

 of .4 mm. at a rate of 9.6 mm. daily. Similar changes resulted in 

 starting and checking growth in much the same manner. At the end 

 of the day the chamber was allowed to cool to give the plant a con- 

 stant temperature of 25° C. and after standing at this temperature 

 for 12 hours measurements were made to determine the rate at this 

 point. 



The rate at 25° C. on the following day varied from 9.6 mm. 

 daily in the morning to 12.6 mm. at 26.5° C, then to 8.8 mm. daily 

 at the close of the day at 26° C. No measurements were made at 

 night but during the two hours beginning at 8 A.M. the rate was 13.2 

 mm. daily at 25° C, after which the temperature was raised to get 

 values for the next ten degree interval. A rate of 17.9 mm. daily 

 was found between 5 P.M. and 10:30 P.M. at temperatures of 

 34-37° C. 



The plant now stood over night at 34-37° C, at a rate of 27 mm. 



PROG. AMER. PHIL. SOC, VOL. LVI, U, JULY 30, I917. 



