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CARNEGIE INSTITUTION OF WASHINGTON. 



7^30™ a. m. and 6 p. m. The following table is a summary of the 

 maximum and minimum amounts of growth (in millimeters) for any 

 day (24 hours) during the course of the two experiments: 



Other experiments by which the same individuals were subjected 

 to varying temperatures for equal periods gave essentially the same 

 results. They also showed in a more exact manner the root response 

 to different temperatures. The root of seedling Prosopis, for example, 

 increases the rate of growth with rise in the temperature of the soil, 

 between 15° and 40° C, in a fairly consistent way. It approximately 

 doubles its growth-rate with each rise of 10° C. The temperature of 

 largest response varies with the experiences of the individual, being 

 higher at the first trials (when youngest) than at subsequent trials 

 (when the root has elongated), although there may intervene only one 

 day between trials, and the entire duration of the experiment may 

 occupy only 5 days. (See table below.) 



Similar studies on the relation of root-growth to soil-temperature 

 show that the growth-rate of Fouquieria roots is not so rapid as in 

 Prosopis at the same temperature, and especially that growth at rela- 

 tively low temperature in Fouquieria proceeds with great slowness. 

 (See above table.) 



