FERTILIZATION IN PIMA COTTON. 



19 



Pima; 90 per cent showed an aperture at 7.05 in the case of King, 

 but not until 8.05 in the case of Pima. Similar observations on 

 August 12 on 50 flowers each of Pima and of the Durango, Acala, and 

 Lone Star varieties of upland cotton indicated, on the contrary, the 

 more rapid appearance of an aperture in Pima than in the upland 

 varieties. The hours at which an aperture had appeared in 50 and 

 in 90 per cent of the flowers examined are shown in Table 10. 



Table 10. — First appearance of an aperture in the corollas of 50 flowers of each 

 of four varieties of cotton grown at Sacaton, Ariz., as observed on August 12, 

 1921. 



• 



Time of opening (a. m.). 



Aperture present- 



Pima 



(Egyptian). 



Upland varieties. 





Durango. 



Acala. 



Lone star- 



In 50 per cent of the flowers 



7.15 

 7.50 



7.40 

 8.10 



7.50 

 8.25 





In 90 per cent of the flowers 



8.55 







While the several observations gave contradictory results as to the 

 relative earliness of the first appearance of an aperture in Pima and 

 in upland varieties, it appears that the further expansion of the 

 corolla proceeds more rapidly in upland than in Pima. Comparing 

 the Pima and Acala varieties it was observed that in the former 

 expansion begins with a very minute aperture at the apex of the 

 bud, which enlarges gradually, whereas in Acala the initial aperture 

 is larger and the petals separate much more rapidly. The greater 

 length of the Pima petals and the fact that they are more tightly 

 wrapped in the bud probably explain this difference. 



The flower of both Egyptian and upland cottons is of brief dura- 

 tion. On sunny days in July and August the corolla begins to wilt 

 and change color by midafternoon, and before sunset the wilting 

 has proceeded so far that the corolla is closed or nearly so and the 

 pistil is becoming flaccid. Abscission of the style in the Pima 

 variety normally takes place within 36 hours after the beginning of 

 anthesis. Observations on 50 Pima flowers in 1922 showed that in 

 every case the style had separated from the ovary by 2 p. m. of the 

 day following anthesis, or 31 hours after the commencement of 

 anthesis. The mean number of hours from the commencement of 

 anthesis to the abscission of the style was 29 ±0.08. 



OPENING OF THE ANTHERS AND DISCHARGE OF POLLEN. 



Examination of flower buds of Pima cotton late in the afternoon 

 preceding the opening of the corolla (PL III, Fig. 1) shows, as a 

 rule, the anthers tightly closed and the pistil free from pollen grains. 

 At this stage the pollen can not be extracted easily from the anthers. 

 Occasional flowers have been observed in which a few of the anthers 

 were open sufficiently in the evening to show the pollen grains, but 

 in none of these cases was pollen found upon the stigmas under 

 conditions making it certain that the discharge had not taken place 

 as a result of rupturing the anthers in the process of cutting away 

 the corolla. In the early morning, however, when the corolla is 



