WATER-STRESS BEHAVIOR OF PIMA COTTON. 21 
the moisture content of soil samples taken in juxtaposition to the 
plants 24 hours after the application of water showed no increase 
above the fourth-foot layer but marked increase in the fifth-foot 
layers. The plants grown under this method of irrigation in 1919 
behaved in a very satisfactory manner and did not show the marked 
slowing up of the growth and flowering rates late in the season 
exhibited by the plants on plats 1 and 2. In 1920 this method of 
irrigation on heavy soil was adopted commercially by Mr. Parker 
and proved very satisfactory. The plants which were irrigated at 
approximately 10-day intervals during the principal fruiting season 
fruited very heavily, with little loss from shedding, and the total 
yield per acre was considerably greater than had been obtained on 
the same soil in several years previously. The encouraging results 
obtained in these tests with a double-row method of cotton culture 
and reports of frequent successes in tests with a somewhat similar 
method at the Bard station point to the need of further experiments 
along this line. There seem to be possibilities of solving several 
important problems of cotton culture under irrigation by perfecting 
some such method. 
CONCLUSIONS. 
This bulletin reports the results of an investigation of the behavior 
of Pima cotton when grown under different conditions of soil mois- 
ture and available plant food in the Salt River Valley of Arizona 
in 1919. 
The normal growing season in the Salt Eiver Valley, while usually 
ample for substantial yields, is none too long for the complete de- 
velopment of the Pima cotton plant, and precaution on the part of 
growers is necessary in selecting a proper date for planting and to 
keep the plants in full activhvy during the limited time available for 
boll production. The occurrence in some years of heavy frosts about 
Xovember 1 has occasioned considerable damage to the late crop of 
bolls. 
The mean period of maturation for over 3,000 bolls of Pima cotton 
was 68 days. 
In Arizona early bolls mature within a much shorter period than 
later bolls. The mean difference in time required for maturation 
between bolls developed from flowers blooming in July and those 
blooming in September was 27 days. 
Plants which had produced the greatest quantity of vegetative 
growth appeared to suffer most frequently from " water stress," re- 
maining longer in a -wilted condition between irrigations and show- 
ing an earlier recurrence of wilting after irrigation. 
The fact that there was no appreciable difference in size or distri- 
bution between the roots of large plants and small plants seems to 
