July 28, 1923 
Growth of Fruiting Parts in Cotton Plants 
199 
LATE SEASON INCREASE IN INTERVAL BETWEEN SQUARES 
There is a tendency for the interval between the appearance of squares 
to lengthen as the season advances. This is shown in Table III which 
gives the number of days between the appearance of successive squares 
on 10 Pima Egyptian plants for three 3-week intervals. In 1921 the mean 
period for the squares produced from June 15 to July 5 was 5.36 days, 
from July 6 to July 26 it was 6.45 days, and from July 27 to August 15 
it was 7.53 days. It can be seen that the mean period for each successive 
three weeks was longer. These data are substantiated by figures on 
Pima at Sacaton in 1920, which showed that the period between the 
opening dates of flowers on successive internodes was gradually increasing. 
This also is shown in Table III. It will be noted that the increase is 
greater in the 1920 data, but this may be ascribed to the fact that the 
period from the appearance of a square until it flowers is slightly increased 
as the season advances, thus tending to make the interval between 
successive flowering dates slightly greater than the interval between the 
appearance of successive squares. 
Table III .—Mean interval between the appearance of successive squares or flowers on 
fruiting branches for three consecutive 3-week periods , at Sacaton, Ariz. 
Period I, 
June 15 to 
July S- 
Period II, 
July 6 to 
July 26. 
Period III, 
July 27 to 
Aug. 15. 
Interval between squares an Pima, 1921... 
Days. 
Days. 
Days. 
5. 36 ±0. 113 
6. 4$±0. 11$ 
7 - 53 ±o- 13 2 
Interval between flowers on Pima, 1 1920... 
5. 91 ± . 068 
7- I4± . 098 
8. 8$± . 231 
1 The intervals are based on flowering periods 30 days later than the square periods used the following 
year. This represents the time from appearance of square to bloom, and places the two series on a com¬ 
parable basis. 
The lengthening of the period between the production of new squares 
has just been shown to be correlated with the advance of the season. 
The possibility that the period lengthens because the new internodes are 
farther out on the fruiting branch naturally suggests itself. The interval 
between the appearance of the first square on a fruiting branch and the 
appearance of the second was figured for the io Pima plants in 1921. 
This interval was compared with the interval from the appearance of the 
second square until the third square appeared, and so with other joints, 
along the fruiting branches. A summary of these data is given in 
Table IV. 
It will be noticed that the period does increase progressively between 
the successive internodes of the branches. The difference, however, is 
slight and it is believed that the reason for the increase is that these nodes 
were produced later in the season, which, as has been shown in Table III, 
results in a longer interval. Such differences, however, were not found 
to be correlated with the node numbers representing their positions on 
the branches. 
When comparisons were made of the interval between the appear¬ 
ance of squares formed during the same three-week period on the 
first and second nodes and on the fourth and fifth nodes of fruiting 
branches, it was found that the interval between squares on the outer 
nodes of lower fruiting branches was practically the same as the interval 
