FERTILIZATION IN PIMA COTTON. 21 



of the Acala variety of upland cotton, on each of six dates from 

 August 3 to August 14. 1920, showed that at about 7 a. m. dis- 

 charge of pollen had begun in only one-third of the flowers. A com- 

 parison was made of the relative rates of opening of the corolla and 

 anthers in Pima and Acala cottons on August 9. 1920. It was ob- 

 served at 7 a. m. that in Pima the corollas were open only 1 or 2 

 millimeters, but the anthers were well open ; while on near-by Acala 

 plants the corollas were open from 5 to 10 millimeters, but the anthers 

 were still closed or were just beginning to split. 



Further observations were made at Sacaton, Ariz., in 1921. At 

 7.30 to 8 o'clock on the cool, cloudy morning of July 27, upland 

 flowers of which the corollas were already open to an extent of 5 

 to 10 millimeters had the anthers in most cases either still closed or 

 split only sufficiently to disclose but not to discharge the pollen 

 grains. Only one of the eight varieties examined showed the dis- 

 charge of pollen in some of the flowers before the corolla had com- 

 menced to expand, while in all closed buds of Pima cotton, which 

 were examined at the same time, the anthers were wide open, and in 

 many of them the discharge of pollen upon the stigmas had begun. 

 On the other hand, on August 12 at 7.30 to 7.45 a. m. examination 

 of closed buds of the Acala variety showed that the anthers were 

 partly open in all cases and that a few pollen grains were present 

 on the stigmas in 7 of the 10 buds examined. 



Observations upon upland cotton have shown that dehiscence of 

 the anthers and discharge of pollen before the petals have begun 

 to unfold are more likely to occur in belated flowers than in flowers 

 which have not been retarded in their opening. Thus, on August 9, 

 1921, a warm, sunny morning, when most of the flowers of upland 

 varieties were already open at 8.15 o'clock, approximately two- 

 thirds of the buds which still remained closed had the anthers 

 partly open. In many of these buds a few grains of self pollen 

 were already present on the stigmas. Closed buds of Pima cotton 

 examined during the same half hour had the anthers much more fully 

 open than in the upland varieties, and in nearly every case the 

 stigmas had received self pollen in greater or -less quantity. On the 

 following morning, with similar weather conditions, observations 

 were made on the Lone Star and Acala varieties of upland cotton 

 and on Pima cotton during the half hour from 8.10 to 8.40, when 

 most of the flowers of the three varieties were partly open. Of the 

 still closed buds of Lone Star, 20 were opened carefully, and 9 of 

 these were found to have the anthers partly open and a few grains 

 of pollen on the stigmas. In the remaining 11 buds the anthers 

 were still closed or were beginning to split but were not yet dis- 

 charging pollen. Of six closed flowers of the Acala variety, four 

 had the anthers partly open and a few grains of pollen present on 

 the stigmas. Ten unexpanded Pima flowers had the anthers much 

 wider open than in the upland varieties, and in most but not all 

 of these a little pollen was present on the stigmas. 



It may be concluded from these observations on the comparative 

 rate of opening of the corolla and anthers in Pima and upland cot- 

 tons that in Pima the opening of the anthers and the discharge of 

 pollen somewhat precede the expansion of the corolla, while in upland 

 as a rule the corolla and anthers begin to open almost simultaneously. 

 In case the opening of the upland corolla has been retarded, how- 



