Hydration and Growth of Colloids and Cell-masses. 



117 



which it is seen that the cells may at times have a temperature 20 C. 1 

 higher than the air. The previous maximum record is that of 51.5 C. 

 for Euphorbia virosa, obtained by Pearson in South Africa in 1913. 2 



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FIG. 22. Temperatures of joints of Opuntia in the open at Desert Laboratory on a day in March 

 and a day in June 1916. The solid line denotes air temperatures, the dotted line the temper- 

 ature of a joint in an east-and-west position with the faces north and south. The broken 

 line gives the course of the temperatuie of a joint with its faces east and west, and showing 

 a drop in temperature when the margin is toward the sun at midday. The upper part of the 

 figure is compiled from the records of March 9, 1916. The lower set of lines is compiled 

 irom the records for June 2, 1916. Redrawn after diagram furnished by Dr. J. M. McGee. 



A proper interpretation of the reactions of the plants used as experi- 

 mental material in the present work might be made only when the ordi- 

 nary exposures were measured, and this was undertaken at the request 



1 Askenasy, E. Ueber die Temperature, welche Pflanzen im Sonnenlicht annehmen. Bot. 

 Zeitung, 33:441-442. 1875. See also U 'sprung, A. Die physikalischen Eigenschaften der 

 Laubblatter. Bibliotheca Botanica, 12: (Heft 60), 68. 1903-4. 



2 Pearson, H. H. W. Observations on the internal temperatures of Euphorbia virosa and Aloe 

 dichotoma. Annals of the Bolus Herbarium, vol. i, part 2. Nov. 1914. 



