AGRICULTURE: REED AND HOLLAND 
137 
unbranched plants. The number of heads produced by the branched plants 
ranged from three to thirteen. 
Rate and Extent of Growth. — Fifty-eight plants were measured at seven- 
day intervals, from the time when each plant was marked 10 centimeters be- 
low the growing tip until no further elongation occurred. On the eighty- 
fourth day/ when the last measurement was taken, the plants averaged 254.5 
centimeters high to the upper side of the head, with a range from 164 centi- 
meters to 339 centimeters. The mean growing period in days was 69.79 
=*= 2.17. The mean height of the plants is shown by figures in table 1, along 
with the standard deviation and coefficients of variability. The mean height 
of plants at seven-day intervals is shown graphically in figure 1. 
50 
40 
30 
2.0 
> 
o 
t- 
10 to 
0 7 H 2.1 18 35 42 19 Sb b3 70 11 81 ' 
Number o\ days 
FIG. 1. GROWTH AND VARIABILITY OF HELIANTHUS 
Mean height of plants 
Standard deviation 
Coefficient of variability 
The data show that the plants rapidly increased in height, the maximum 
growth rate being exhibited between the thirty-fifth and the forty-second days, 
i.e., about the middle of the grand period of growth. The growth rate was 
smaller at the start, rapidly increasing until it reached its niaximum and then 
declining as it approached the end of the grand period of growth. 
The standard deviations of the mean values increase as the means increase 
but not at a proportional rate. In this case the coefficient of variabihty is a 
better measure of the variability since its size is more nearly independent of 
the height of the plants. This coefficient does not increase during the latter 
