942 
Journal of Agricultural Research voi. xxra, No.» 
Shedding as a direct effect of irrigation was not indicated, even on the 
“heavy” borders, although it is generally believed that excess moisture 
may cause young bolls to drop. There was no generally higher or 
lower rate of shedding at any regular interval after a border was irrigated. 
This can be seen in figure 3, or by a comparison of the irrigation dates 
with the daily shedding record in Table VII. That the plants retained 
their normal fruitful behavior throughout the experiment instead of be¬ 
coming overgrown is regarded as responsible for the lack of any exces¬ 
sive shedding. The highest shedding rate, 15 per cent, occurred on the 
“heavy” border C1-5, in which the plant growth was checked, appar¬ 
ently by too much water. But this rate of shedding was nearly equaled 
on the “medium-heavy” border Ci-10, which showed no abnormal 
behavior. 
The length of the period between the date of flowering and the date of 
shedding of young bolls was found to fluctuate, with no indication of 
being affected by irrigation as applied. It is shown in Table VIII that 
82 per cent of the shedding occurred between 4 and 14 days after the 
flowers opened, with a maximum 8 days after flowering and 10.8 days 
as the average age of shed bolls. That so little shedding occurred until 
several days after flowering is of interest and would agree with results 
published by Lloyd 10 for Upland varieties, who found that “abscission 
is inhibited dinring anthesis,” but there are differences between the Up¬ 
land and Egyptian types with respect to the time of maximum shedding, 
Lloyd found under field conditions in Alabama that the period of greatest 
shedding of young bolls was from 4 to 8 days after flowering and that 
“the age at which bolls were shed in maximum numbers was 5 to 6 
days,” while his figures show that the average period of persistence was 
about 6 days. Thus there are definite indications that Upland bolls shed 
earlier in Alabama than Pima bolls in Arizona. 
In 1918 Mr. C. J. King, of the Bureau of Plant Industry, found the 
mean period of persistence of shed bolls in Pima cotton at Phoenix, 
Ariz., to be 10.3 days after flowering, 11 which is in close agreement with 
the period of 10.8 days obtained in our experiment at Sacaton. 
Under Sacaton conditions, the Egyptian cotton differs notably from 
the Upland varieties, which often shed a large proportion of their buds 
before flowering. This was especially noticeable in 1920, when two 
Upland varieties, Durango and Lone Star, were compared with Pima 
cotton. Until the latter part of the flowering season the great majority 
of the squares produced on the Upland plants were dropped, while the 
adjoining border of Pima cotton lost very few squares. As in the irri¬ 
gation experiment, the shedding which took place in the Pima border 
was almost entirely of young bolls. Lloyd found in Alabama that about 
50 per cent of the shedding in the Upland varieties consisted of squares. 
Factors which caused shedding in the experiment were probably of a 
general nature, as the percentage of shedding was practically the same 
throughout the Pima cotton on the station that was receiving a normal 
treatment. Less shedding occurred than usual, which may be ascribed 
to the lack of heavy summer rains, the few rains being too slight to affect 
the amount of shedding. Lack of fertilization of the flowers caused 
10 1,1.0yd, Francis E. the abscission op flower-buds and fruits in gossypium, and its relation to 
Environmental changes. In Trans. Roy. Soc. Canada, ser. 3, v. xo, sect. 4, p. 55-61. 1916. 
- environmental changes and their effect upon boll-shedding in cotton. In Ann. N. Y. 
Acad. Sci., v. 29, p. 1-131, 26 fig. 1920. literature, p. x29-i3t. 
31 King, C. J. water-stress behavior of pima cotton in Arizona. U. S. Dept. Agr. Bui. 1018. p. 15. 
1922. 
