MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 303 



peared to be slightly limp, suggesting that elongation and shorten- 

 ing might be a matter of the balance between water accession and 

 loss. 



The shoot was now subjected to a temperature above 43° C. con- 

 tinuously for two days, the maximum being 52° C. Its body 



Fig. 2. Auxographic tracing of variations in length of shoots of Opuntia 

 at high temperatures in dark room at Carmel, September i, 1916. The sheet 

 is ruled into two-hour periods by arcs and the 10 mm. horizontal lines of the 

 millimeter sheets are reproduced. The variation in length is magnified 26 

 times, (a) Downward movement of pen 7:30 A.M. to 9:40 A.M. denoting 

 growth at temperatures of the stem of 45° to 49° C. (b) Growth checked 

 for 20 minutes at 49° C. (c) Growth resumed at temperature of 49° C. (d) 

 Shortening at 48.5° to 52° C. (e) Stationary at 50.5° C. (/) Growing at 

 temperatures of 48° to 49° C. (g) Shortening at 49° C. (h) Growing at 38° 

 to 41° C. (0 Shortening at 49° C. 



