413] E. 8. Johnston 215 
height, for healthy buckwheat plants, during the spring, sum- 
mer and autumn. ; 
McLean * 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. 
