976 
Journal of Agricultural Research 
Vol. XXXI, No. 10 
or the final resultant of the growth processes, is to a considerable 
degree subject to modification by environmental conditions. On the 
other hand, Tc of equation (1) is a specific constant and represents 
certain inherent qualities of growth of the organism. In equation 
(2) K=TcA , and hence after application to the observational data 
1c of equation (1) may be estimated from A and K of equation (2) 
as Tc= K/A. According to this view K/A affords an index of genetic 
significance as representing the inherent rate or velocity of growth 
characteristic of the organism. Thus Robertson 6 finds that British 
male infants under the dissimilar environments of England and 
Australia have dissimilar values of A , namely 318.0 and 341.5, 
respectively, but similar values of K/A, namely, 0.000399 and 
0.000398, respectively. The inference is that like heredity leads to 
like values of K/A, even though the environment is such as to lead 
to unlike values of A in the growth equations. If the constant has 
this genetic significance it affords a highly valuable measure of 
growth and inherent growth limitations. 
In agricultural practice we are concerned with the final growth 
attained by the crop, and generally this is identical with A of the 
equation. In some cases, as will appear later, it is necessary to assume 
a higher value for A than that represented by the crop yield. It is 
apparent, therefore, that so far as affected by the value of A, the 
constant K/A varies in an inverse ratio to the crop yield. It will be 
seen in Figure 1 that a high value of K means a short-growing period, 
and quite naturally a short-growing period tends to be associated 
with a low-crop yield. Therefore the effect of K tends to give also 
an inverse ratio of the constant K/A to yield. 
Conversely, A /K will tend to vary directly with crop yield, and 
consequently the constant in this form is somewhat better adapted 
for use in comparisons. Where K/A is a specific constant repre¬ 
senting inherent growth velocity (that is, the rapidity with which full 
growth is accomplished, not the rate of absolute growth increase), 
A/K is a specific constant representing inherent final growth capacity . 
A/K is to be regarded, of course, simply as the reciprocal of Tc of 
equation (1). Its value as an index of growth capacity or crop yield 
depends upon the association between the length of time that the 
crop or crop constituent under consideration continues to grow and 
the final extent of growth. Experience indicates that length of grow¬ 
ing period and extent of growth or crop yield are directly associated. 
On this reasoning the constant A/K should represent the inherent 
capacity for crop yield as between genetically different varieties or 
species under optimum or comparable conditions of environment. 
How well it may actually serve such a scientifically important and 
practically useful purpose remains to be demonstrated by critical 
experiment. 
The data of the present paper pertain to the sunflower crop and 
the corn crop, the data for corn being derived from the work of 
Jones and Huston. 7 The data pertain not to individual plants di¬ 
rectly but to acre populations collectively. In the graphic presenta¬ 
tion the same scale is used for time in days throughout, but the scale 
6 Robertson. T. B. Op. cit.p. 40. 
7 Jones, W. J. and Huston, H. A. composition of maize at various stages of its growth. Ind. 
Agr. Exp. Sta. Bui. 175: 599-630, illus. 1914. 
