WATER-STRESS BEHAVIOR OF PIMA COTTON. 



19 



It will be seen from Table VIII that the greatest number of 

 flowers per plant was produced on plat 1, to which the greatest 

 quantity of water had been added. However, on account of the 

 greater amount of shedding on this plat there was a smaller number 

 of bolls set by October 1 than on plat 3, which had received the least 

 water. The " potential seed-cotton production " on October 1 of 

 plants on plat 3 exceeded that of any other plat, but the " potential 

 seed-cotton production " is not in accord with the actual production, 

 as determined upon picking. This discrepancy can be accounted for 

 by the records of frost damage to bolls, as shown in Table VII, the 

 percentage destroyed having been greater in plat 3 than in plat 1. 

 Bolls set late in September were not able to develop fully, and those 

 which cracked open sufficiently to be picked were lighter in weight 

 than those set earlier in the season. 



Table VIII. — Comparison of the flowers produced, the percentage of shedding, 

 the bolls set, and the potential seed-cotton production in each of four plats of 

 Pima cotton with the total yield of seed cotton per acre in 1919. 



Plat. 



Mean num- 

 ber of flowers 

 produced. 



Mean per- 

 centage of 

 shedding. 



Mean num- 

 ber of bolls 

 set by 

 Oct. 1. 



Mean 

 potential 

 seed cotton 

 produced 

 (grams). « 



Yield of 

 seed cotton 



per acre 

 (pounds). 



No.l 



58. 2± 1.79 

 50. 9± 1.78 

 57.0±2.16 

 48. 2± 1.30 



26. 5± 0.38 

 21. 6± .34 

 16. 7± .21 

 17. 8± .26 



43.1 ±1.71 

 40. 0± .40 

 47. 6± 1.89 

 39. 7± .36 



106 

 96 



111 

 95 



1,602 



No.2 



1,437 



No.3 



1,496 



No.4 



6 1,397 







o Mean "potential seed-cotton production" in the sense here used is the mean weight of seed cotton per 

 boll as determined upon picking, multiplied by the mean number of bolls set perplant on Oct. 1. 



b The presence of a "slick spot" of approximately 900 square feet in plat 4 was responsible in part for the 

 low yield on that plat. This soil variation was not noted until its presence was indicated by the stunted 

 condition of the plants. 



Such data, Tables VII and VIII, seem to indicate that every pre- 

 caution should be taken in growing cotton in areas where there is 

 danger of damage from early frosts to stimulate the setting of fruit 

 to the fullest extent during the months of July and August. The 

 data show that the first irrigation on June 10 was not so early that 

 it produced an excessive number of vegetative branches but served 

 the purpose of stimulating the plants into early fruiting, which was 

 especially important for that particular season. The 16 days lost 

 by the plants in plats 3 and 4 in the early processes of fruit produc- 

 tion was a handicap that they never overcame. While the cessation 

 of growth and flowering immediately after the 1st of September 

 might result in a reduction of the yield, such loss of time under Salt 

 River Valley conditions would hardly result so seriously as an equal 

 length of time lost at the beginning of the fruiting season. 



The more pronounced slowing in late summer of the growth 

 rate and flowering of cotton plants which had produced a heavy 

 growth of vegetative material early in the season presents a very 

 interesting physiological problem. The work of some recent investi- 



