6 
BULLETIN" 1018, U. S. DEPARTMENT OF AGRICULTURE. 
Balls (3) gives 48 days as the mean for standard Egyptian Mit Ann 
at Cairo, and Harland (14) reports 51 days for the mean of Sea Is- 
land cotton in the West Indies. 
The mean development period, as determined for 3,319 bolls of 
Pima cotton at Phoenix, Ariz., during the season of 1919, was 68 days. 
.Results 3 obtained by Leding at Sacaton, Ariz., which indicated that 
the length of the period of development of the boll for the Pima 
variety during the season of 1918 averaged 67 days would seem to 
substantiate the above data as to the mean lengths of the development 
period. Mr. Leding's data also conforms to that of the writer in re- 
gard to the lengthening of the period as the season advances. 
The lengthening of the period of development of the boll in the 
later months, as shown in Table II, is also in agreement with the re- 
sults reported by Allard (1) and Ewing (12) in the Southern States, 
showing that the early bolls matured within a shorter period than the 
later bolls. While the climate of the Salt River Valley is reported 
to be similar in many respects to that of the Nile Valley in Egypt, 
it would appear from the reports of Balls (3) that no such lengthen-' 
ing of the boll period occurs there. Balls speaks, however, of the 
effects of environmental influence on the boll period and states that it 
is eight da}^s longer in the Middle Delta than at Cairo. It is also 
apparent from the reports of Harland (14) that no such lengthening 
of the boll period occurs in the tropical climate of the West Indies. 
From a study of the results shown in Table II, it would appear 
that there is no relation between soil-moisture conditions and the 
period of boll development. It also seems evident from the results 
shown in Table II that the heavy application of fertilizer containing 
10 per cent of available phosphoric acid had little or no effect in 
hastening the maturity of the bolls produced on plat 4. 
Table II. 
Monthly variation in the development period of the holls of Pima 
cotton in 1919. 
Plat. 
Average ' Length of period (da5 T s) for flowers 
soil° opening in— 
moisture |_ 
during 
flower 
production 
I (percent). 
No. 1 5.0 
No.2 1 3.1 
No. 3 ! 2.5 
No. 4 2. 8 
Mean temperature, °F : . . . 
Jul v. 
55. 8± 0.14 
54. 4± .IS 
53. 2± .13 
53. 2± .15 
76.5 
September. 
WATER-STRESS BEHAVIOR. 
The irrigation on June 10 of plats 1 and 2 caused the plants in 
these plats to grow more rapidly than those in plats 3 and 4, which 
•Unpublished. Kindly furnished to the writer for use in this bulletin. 
