WATER-STRESS BEHAVIOR OF PIMA COTTON. 
11 
Table IV shows a striking contrast in the quantity of water used 
by the plants on plats 1 and 3 during May and June. The table also 
shows that during the month of June more than tAvice as much 
water was lost from plat 1 as from plat 3. The difference is all the 
more striking in view of the fact that the direct evaporation from 
the soil surface must have been less on plat 1 because of the shade 
afforded by the large plants (PL I). On July 8 the average height 
of plants in plat 1 was 7.5 inches greater than the average height of 
the plants in plat 3. Table IV further shows that, when calculated 
to an acre basis, plat 1 produced 1,413 pounds more of dry matter 
than plat 3. The water requirement (pounds of water expended 
per pound of dry matter produced) is shown to be about 5 per cent 
greater for plat 1 than for plat 3. 
Table V. — Comparison of the height of Pima cotton plants and the percentage 
of shedding on plats 1 to 4 in 1919. 
Total 
bolls 
Height, 
shed 
Plat. 
Sept. 1 
prior 
(inches). 
to 
Oct. 1 
(percent). 
No. 1 
63 
55 
54 
50 
26.6 
No. 2 -. 
21.5 
No. 3 
16.7 
No. 4 
17.8 
WATER RELATIONS AND THE SHEDDING OF IMMATURE BOLLS. 
From Table V it will be seen that the greatest percentage of shed- 
ding occurred on the largest plants growing in soil which constantly 
contained the greatest quantity of available moisture. Such an 
occurrence would seem to be at variance with that observed by many 
investigators who have studied the shedding of the Upland cotton 
plant. 
Barre (5. p. 23-24) states that "lack of sufficient soil moisture 
is the principal factor in determining shedding." Ewing (1%) con- 
cludes " that a deficient supply of soil moisture will result in exces- 
sive shedding." Balls (4) in reporting shedding studies with Egyp- 
tian cotton states that " shedding becomes abundant toward the end 
of the interval between irrigations and decreases directly after water- 
ing, but finally becomes excessive again when the water level is raised 
and the lower soil becomes saturated." Evidence, however, is not 
lacking that the water content of the plant itself may be an important 
factor in furnishing the stimulus for the shedding of squares and 
young bolls, and to the writer it appears significant that most of 
the investigators have proposed this factor as bearing an important 
relation to abscission. Harland (14) credits No well with the state- 
