Mar. 34,1933 
Summer Irrigation of Pima Cotton 
933 
Shedding data were obtained by placing dated tags on all the flowers, 
the tags being fastened to the pedicels of the flowers so as to remain 
attached even if the flower or young boll was shed and fell to the ground. 
Each day when new flowers were being tagged, all of the young bolls 
which had shed were picked up and their flowering and shedding dates 
were recorded. 
GROWTH OF THE PLANTS 
' During the early stages the plants developed rather slowly. The 
prevailing cool temperatures of April and May somewhat retarded the 
growth, and the plants averaged only 8 inches high in the latter part of 
May. An increased rate of growth was recorded in June, when the 
weather became very warm, but water was withheld in order to check 
any tendency for the plants to become rank or to produce vegetative 
branches. At the same time careful watch was kept to see that there 
was sufficient moisture available for a steady growth. The increase in 
height of the plants was approximately 10 inches during the month of 
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Fig. i.—D aily maximum and minimum temperatures and precipitation at Sacaton from June 15 to 
September 15. 
June. After the irrigation of July 2, when the experimental treatment 
began, the plants grew more rapidly but maintained a normal, fruitful 
habit. 
Later development was marked by the uniformity of growth in all 
borders, notwithstanding the diversity of irrigation treatments. As 
shown in Table IV, which gives the average growth per week of 25 plants 
in each border and the average increase per week of the three borders 
that were treated alike, the development of the plants was at about the 
same rate throughout all the borders. It will also be seen that the plants 
in all the borders grew rapidly during July and early August, averaging 
an increase of 4.5 inches per week. During the week August 12 to 19 
a decided decrease in the rate of growth was recorded in all borders, the 
plants growing an average of only 1 inch. A comparison of Table V 
with the climatological data presented in figure 1, shows there was no 
decided drop in temperature coincident with this retardation of plant 
growth, but during that week two small showers fell and there was gen¬ 
eral cloudiness of the weather. There is no reason to believe that mois¬ 
ture deficiency was the cause of the lower growth rate, as five of the nine 
borders had been irrigated on August 13, whereas the slower growth was 
recorded in all the borders. An increased rate of growth was obtained 
