^54 
H. S. REED 
growth rate between the 35th and the 4.26 days, i. e., about the middle of 
the grand period of growth ; the rate then declined as the end of the grand 
period of growth was approached. 
A great decline in the growth rate of the plants began to appear as the 
flower bud on the apex of the stalk began to be differentiated. As the 
''head" developed, the growth of the stalk became slower, showing agree- 
ment with the condition which Pearl and Surface (1915) found when the 
tassel is formed on maize. After the flowers cf the composite "head" had 
^80 
2^0 
160 
120 
80 
40 
/ 
f 
/ 
y 
y 
so 
40 
50 
20 
10 
7 14 U ^8 35 ^2. 49 56 63 70 7 7 84 
Fig. I. Curves showing progressive changes in mean height, standard deviation and 
coefficient of variability of sunflower plants during the grand period of growth. 
Mean 
Standard Deviation. 
Coefficient of Variability. 
been pollinated, there was no further elongation of the stalk. It is probable 
that from this time on the growth forces of the plant are devoted to seed 
formation instead of to elongation of the stalk. Thus, variability in the 
time of blossoming may, and undoubtedly does, influence the grand period 
of growth and the total growth of this plant. When the flowers of the head 
have been pollinated, the head, which previously stood erect, becomes 
pendant. The floral surface, which is uppermost during the prepollination 
process, is lowermost during the post-pollination period. 
