18 



BULLETIN 1018, U. S. DEPARTMENT OF AGRICULTURE. 



in plat 1. Following this week the plants in plats 1 and 2 were 

 never so responsive to the influences which affect flowering as those 

 in the other plats, and their curves dipped with considerable regu- 

 larity after September 3 to a condition of almost complete cessation 

 about September 30. The curves of plats 3 and 4 also dipped toward 

 a hibernation period, but with greater fluctuation and a greater 

 amount of flower production. 



It will be observed that during this period of gradual cessation 

 in flowering the different plats held about the same relative position 

 in regard to the moisture content of the soil as at the beginning of 

 the flowering season, plat 2 having usually the second highest and 

 the moisture content of the other two plats having been almost con- 

 stantly smaller than that of plats 1 and 2. 



Data given in Table VII indicate that some economic importance 

 may be attached to such an occurrence, especially in seasons when 

 the first killing frost of the autumn does not arrive earlier than 

 is commonly expected for the vicinity. A summary of the data 

 obtained by the Weather Bureau shows that the average date of 

 the first killing frost at Phoenix, Ariz., during the years 1895 to 1920 

 is December 3, or 33 days later than the date on which cotton was 

 killed by the frost in 1919. 



Table VII. — Comparison of flowers produced and stem growth prior to August 

 15, plants producing vegetative branches, bolls produced on 20 plants during 

 September, and September bolls destroyed by frost on four plats of Puna 

 cotton in 1919. 





Percentage of— 





Plat. 



Total flowers 



produced 

 during first 

 45 days be- 

 ginning with 

 initial date 

 of flowering. 



Total stem 

 growth pro- 

 duced prior 

 to August 

 15. 



Plants 

 producing 

 vegetative 

 branches. 1 



September 



bolls 

 destroyed 

 by frost. 



Bolls 

 produced 

 on 20 

 plants 

 during 

 September. 



No.l 



60. 5 ±0.97 

 58. 6± 1.01 

 48. 9± 1.00 

 46. 8± 1.08 



85.3 

 80.4 

 76.2 

 76.9 



5 



40 

 10 

 10 



49±2.2 

 60±2.3 

 61±1.8 

 59±2.1 



263 



No.2 



215 



No.3 



340 



No. 4 



264 







1 Most of the vegetative branches made only a rudimentary development. The flowers produced were 

 so few as to have no material effect on the flowering curves or the final yield. 



From the data in Table VII it is apparent that plats 1 and 2 

 would have produced considerably more cotton per plant despite 

 the early frost had the later flowering continued at the same rate 

 as that on plats 3 and 4. The relative production of both stem growth 

 and bolls was considerably greater during the first 45 daj-s of the 

 flowering season on plats 1 and 2 than on plats 3 and 4. This may 

 be attributed to the fact that plats 1 and 2 received their first irriga- 

 tion 16 days earlier than plats 3 and 4. 



