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 (H) 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 deA^elopment 

 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 days 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 l>olls of Pima 



cotton in 1919. 





Plat. 



Average 



soil 



moisture 



during 



flower 



production 



(per cent). 



Length of period (days) for flowers 

 opening in — 





July. 



August. 



September. 



No. 1 



5.0 

 3.1 

 2.5 



2.8 



55. 8± 0.14 

 54. 4± .38 

 53. 2± .13 

 53. 2± .15 



76. 5 



69. 5± 0.30 

 68. 3± .35 

 67. 5± .30 

 66. 2± .30 



75.9 



80. 4± 1.76 



No. 2 



SO. 9± 1.91 



No. 3 



85. 4± .42 



No. 4 



81. 1± .49 



Mean temnerature 



°F 



69.0 











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. 



