413] E. 8. Johnston 215 



height, for healthy buckwheat plants, during the spring, sum- 

 mer and autumn. 



McLean 2 has pointed out the approximate proportionality 

 of the rates of production of dry weight and leaf surface, 

 for the first four weeks of growth of soy-bean plants, and he 

 also found that the rate of stem elongation varied quite differ- 

 ently from the rates of production of dry weight and surface. 

 It may be of- fundamental significance that two plants as 

 widely different, in many other respects, as are buckwheat and 

 soy-bean, exhibit these remarkable agreements in the manner 

 of variation in these three growth-rates with differences in 

 the climatic conditions of the environment. 



The general agreement between the seasonal variations 

 shown by the rates of increase in dry weight and in leaf area 

 is so marked that it appears quite permissible to combine these 

 two criteria by averaging their relative values, to give a single 

 value representing both together, and the averages so derived 

 are given in the last column of the table. Of course, these 

 two measurements of growth-rate are not directly commensu- 

 rable, and the average values here introduced are to be re- 

 garded merely as numerical indices of the rates of growth. 

 This value has its maximum (1.00) for the period ending 

 May 22, and it of course shows high value for the five fol- 

 lowing periods. Its minimum value (0.39) occurs for the 

 period ending Oct. 23. 



Of course there are many other considerations to receive 

 attention in a study of this sort, but it already seems clear 

 that a regular and pronounced seasonal variation in the rates 

 of production of dry weight and leaf area may be expected in 

 healthy buckwheat plants growing in a greenhouse in this 

 kind of climate, although the same nutrient medium is al- 

 ways employed. If the weight-area indices be represented 



2 McLean, Forman T., "A preliminary study of climatic conditions 

 in Maryland, as related to plant growth." Physiol. Res. 2: 129-208. 

 1917. 



