AGRICULTURE: REED AND HOLLAND 
141 
hundred, a random sampling would give values diverging more widely from 
the theoretical than those actually found. 
Since the observed yalues agree so well with the theoretical values, it seems 
safe to assume that the growth rate is governed by constant internal forces 
rather than by external forces which would be expected to be more casual in- 
operation. 
The theoretical values for the consecutive increases in the mean height of' 
the plants give a smoother curve than the observed values give, as shown in 
figure 2. The sag in the observed curve near the twenty-eighth day does not 
appear in the theoretical curve. The summit of the theoretical curve is near 
280 
0 7 M II 2.8 35 At 49 56 W ^0 11 M 
Number da^s 
FIG. 3. COMPARISON OF OBSERVED AND CALCULATED VALUES FOR THE MEAN HEIGHT OF 
HELIANTHUS 
Observed 
Calculated — — — — — — — — 
the thirty-fifth day, thus agreeing with the computed value of h = 34.2 days, 
the time at which half the final height is attained and at which growth is most 
rapid. 
The assumption having been made that the growth was more largely gov- 
erned by internal than external factors, and positive evidence in favor of the 
assumption having been obtained, it is next in order to investigate the 
relationship between growth and some of the more prominent factors of the 
external environment. 
Temperature is known to have a potent effect upon growth, especially if 
it departs widely from the optimum requirements of the organism. In a prob- 
