GROWTH AND VARIABILITY IN HELIANTHUS 
meters, sixty of the normal-appearing plants were selected at random 
throughout the small plot and marked with suitable labels. (Two plants 
were subsequently discarded on account of accident.) Each plant was 
marked with India ink at a distance of ten centimeters below the growing 
tip. This mark served as a point from which further measurements were 
made. Adjacent plants were removed from the vicinity of those selected 
so that a space of at least 20 centimeters intervened between any plant and 
its nearest neighbor. In short, environmental conditions were made as 
nearly uniform for the individuals in this small group as it was feasible to 
make them under field conditions. In the latter part of July the terminal 
buds began to develop into blossoms, and coincidentally the plants ceased 
to elongate. 
The population contained both branched and unbranched individuals. 
The branched form usually produces a head on the apex of each branch, 
whereas the unbranched form produces only one head and that develops 
from the apical bud of the stem. The branching habit is regarded by Shull 
(1908) as a Mendelian character. One important difference should be 
noted between the plants described by Shull and those here considered, 
viz. : Shull's plants branched from the lower nodes of the stalk, while these 
branched only from the upper nodes. 
Church (191 5) regards the branched form as a mutant of the unbranched 
and believes that it is the oldest mutation on record. 
This mixture of branched and unbranched stems is not thought to 
affect the validity of the measurements upon which the present study is 
based, since only 17 out of the 58 plants were branched and the average 
heights of the two classes at maturity were close enough together to be 
within the range of the probable error. The average growing period of the 
branched plants was 4.6 days longer than that of the unbranched plants. 
The number of heads produced by the branched plants ranged from 3 to 13. 
Rate and Amount of Growth 
The measurements made on the 58 plants are given in table i, which 
shows the heights of the individual plants at seven-day intervals, dating 
from the time when each plant was marked 10 centimeters below the growing 
tip and continuing until no further elongation occurred. On the 84th day, 
when the last measurement was taken, the plants averaged 254.5 centi- 
meters high to the upper side of the head, with a range from 164 centimeters 
to 339 centimeters. 
The measurements of all plants have been assembled for study en bloc 
(table i). The mean height of the plants at seven-day intervals is shown 
by figures in table 2, together with the standard deviations and coefficients 
of variability. The mean height of plants at seven-day intervals is shown 
graphically in figure i . 
The data show that the plants grew slowly at first, reached the maximum 
