11 



climatic rneas-are.iients in question. The second step consists 

 in weighting avarage values in such a way as to furnish a 

 second series of values that express the climatic conditions 

 as they affect the lolants . It is clear, for example, that the 

 readings of a therrcoxeter do not express the effectiveness of 

 tenipersture to accelerate or retard ;f)lant growth. It there- 

 fore becoraes desirable to re-clace the -actual thermometer read- 

 ings Tjy a series of weighted values, more or less d,i, re-^.tly pro- 

 portional to the temperature effect upon the growth of the 

 ■plants. O-^ing to lack of information of a quantitative nature 

 as to the relation het'.veen olant growth and environmental tem- 

 perature, this can be accomplished only in a tentative and 

 approximate v:aj at the present time, llo sttempts have yet 

 been made to derive such weighted values to represent the 

 effectiveness, for lolant growth, of any other climatic condi- 

 tinn. 



The consideration of temperature , light, and evapora- 

 tion now to be g:iven will show how the original climatological 

 data have been grouped for comparison with the plant growth 

 measurements and haw the average values have been handle 1 in ""he 

 present study. 



