n 



all the cultures of the study. 



To obtain the original or absolute plant or climatic 

 value from the relative value as given in the tables of 

 this paper, it is necessary only to reverse the arithmetical 

 procedure by which the relative value was derived, j'or ex- 

 ample, suppose it was desired to get thejactual mean daily rate 

 of increase in leaf-area ver plant for the four-week period 

 beginning Aug. 5, and for the station at Ooleman. The relative 

 value given in the table is I'^B. The first operation is to 

 divide by 100, which gives 1.08 as the true relative value; 

 The average daily in'^reT»ent in leaf arv^a per plant, for the 

 period and stati '-n in question, was therefore i.06 times the 

 value of the common unit employed for this process of increase 

 in leaf area. IJulti plying thus unit value Q22 sq. mm.) 

 as given in talble I by 1.08 gives 132. sq. mm. as the 

 average daily increment required. To obtain the average 

 total leaf area per plant at tlie end of the period in ques- 

 tion, we multiply 132,0 sq. mm. by the number of days in the 

 period f 28 in this case) and get 3698 sq. mm. Since there 

 were 5 plants ;neasured in this culture, the total leaf area for 

 the entire culture at the end of the period is obtained by 

 multiplying 3698 sq. ram. by 5, which gives 18490 sq,mm. or 

 184.9 sq. cm., which is the actual areal value detexmined 

 from the prints of these leaves. All of the original ab- 

 solute values may be obtained from the relative ^nes in a 

 similar manner. It is of coitrse evident from the above de- 

 scription of the m^anner in whj ch the relative values have 

 been derived that they are proportional to the corresponding 



absolute valuss. In all subsequent discussion, when plant 



