406 



Plant Physiology 



SUM or DAILY MEAN TEMPERATURES ABOVE 18 C. (64.4 F.) FOR 

 FRUITING PERIOD OF DATE-PALM FROM MAY 1 TO OCT. 31 



case of the F. scale it is necessary, of course, to subtract 32 from the daily 

 mean before multiplying for the product. It would seem, however, that 

 the method of computation to be preferred is one whereby an approxi- 

 mate growth minimum is taken as the basis, and the difference between 

 this and the daily mean represents the daily efficiency during the grow- 

 ing period. An example in the latter case is as follows : assuming the 

 growth period of wheat to be 100 days, the minimum growth temperature 

 40 F., and the daily mean to be 70 F., we have 70 40 x 100 = 3000 F. 



