WATER-STRESS BEHAVIOR OF PIMA COTTON. 5 
half of the cotton acreage in the Salt River Valley. No estimate was 
made by the writer for the whole valley, but in several fields visited 
it appeared that from 30 to 40 per cent of the bolls had been de- 
stroyed. The variation in season from year to year will not permit 
any rigid rule to be fixed for a critical date of planting, and conse- 
quently mistakes are made in planting too early as well as planting 
too late. The prolonged period of frosts and low temperatures oc- 
curring in late March and early April, 1920, was responsible for very 
heavy loss to the cotton growers of the Salt River Valley on ac- 
count of the poor stands which resulted. 
The Pima cotton plant will continue to develop bolls during a 
long period when environmental conditions are favorable. The 
writer has observed flowers to be still appearing on plants which had 
commenced flowering 150 days previously. However, the normal 
period of flowering for the Pima variety in the Salt River Valley is 
from 90 to 110 days. Results by Ewing (12) in Mississippi and Lloyd 
(19) in Alabama show that the length of the flowering period in those 
States for Upland varieties is from 40 to 80 days. The flowering 
curves of Balls (3) show that in Egypt the flowering of Egyptian 
varieties continues through a period of 120 to 140 days, while flower- 
ing curves for Sea Island cotton in the West Indies as presented by 
Harland (llf.) show that the duration of the principal fruiting 
period there is from 140 to 150 days. 
In Egypt Balls (3) places considerable importance on " the time 
of arrival " of the cotton crop ; this is not so much because of frost 
damage as because of the injury resulting from " root asphyxiation," 
when the water table rises in late summer. After the flood season of 
the 'Nile, when the water table has been lowered, the flowering often 
revives and continues through October and into November. Har- 
land (14) states that in the West Indies the time of arrival of the 
crop is not of practical importance. In Arizona the general tendency 
of the Pima variety is to continue flowering at a somewhat reduced 
rate throughout the month of September, but not infrequently many 
of the bolls set during this month are damaged or destroyed by early 
frosts. 
The percentage of bolls set in September, 1919, which reached ma- 
turity on the heavy soil above described in which the seed was planted 
on April 5, was as follows: Plat 1, 51; plat 2, 40; plat 3, 39; plat 
4,41. • 
The period of maturation for bolls of Pima cotton, as derived from 
the data obtained by the writer during the season of 1919, is consid- 
erably longer than that given by any commercial variety reported to 
cotton literature. Ewing (12) gives the mean length of the boll- 
development period of small-boll Upland long-staple varieties in 
Mississippi as 51.5 days and for small-boll early varieties 48.5 days. 
