FERTILIZATION IN PIMA COTTON. 



45 



small departure from the 50 per cent to be expected if the two pollens 

 compete upon equal terms. It would therefore seem that while 

 Egyptian pollen is very strongly prepotent over upland pollen on the 

 Egyptian stigmas, there is no corresponding prepotency of upland 

 pollen on the upland stigmas. 



EXPERIMENTS AT SACATON, ARIZ. 



DEPOSITION OF THE TWO POLLENS NOT SIMULTANEOUS. 



An experiment was performed in 1916 with the object of determin- 

 ing in what degree pollen of a distinct but related variety may com- 

 pete with automatically deposited self pollen. Flower buds on sev- 

 eral plants of Pima cotton were bagged early in the morning but 

 were not emasculated. At about 10.30 o'clock the stigmas were 

 thoroughly smeared with pollen of the Gila variety, which is also 

 of the Egyptian type, and the bags were replaced. Seed from the 

 resulting bolls was planted in 1917 and the plants were thinned in 

 such manner as to avoid any selection. Of the 240 plants which re- 

 mained after thinning 34, or 14.2 ±1.5 per cent, were classed as 

 hybrids (Pima X Gila F x ) and the remainder as pure Pima. We 

 may therefore conclude that 86 per cent of the ovules had been self- 

 fertilized in flowers which had received an abundance of foreign 

 pollen. 



In order to ascertain whether pollen of a very different type may 

 compete better with self pollen than pollen of a related variety, an 

 experiment was performed in 1919. Two flowers each on a number 

 of plants of Pima (Egyptian) cotton were bagged in the evening, 

 but were not emasculated, thus permitting automatic self-pollination 

 to proceed in the normal manner. At about noon of the following 

 day the stigmas of one flower on each plant were smeared with pollen 

 of the Gila variety of Egyptian cotton, and the stigmas of the other 

 flower were smeared with pollen of the Acala variety of upland cot- 

 ton. In 1920, populations were grown from the seed resulting *from 

 each self + cross-pollination, all plants which developed having been 

 left in place until the percentages of first-generation hybrids (PimaX 

 Gila and Pima X Acala, respectively) had been determined. The re- 

 sults are stated in Table 26 (upper part) . 



Table 26. — Hybrids resulting from seed produced by flawers of Pima cotton 

 which, in addition to having been automatically self -pollinated, had been 

 cross-pollinated with pollen of Gila and of Acala cotton, respectively, in 

 1919 and with pollen of Acala in 1920. 



Season and character of pollination. 



Plants. 



Fi hybrids. 



Number. 



Per cent. 



Season of 1919: 



Gila (Egyptian) 



206 

 287 



74 

 96 



35.9±2.3 



Acala (upland) 



33.4±1.9 







Difference 



2.5±3.0 





479 



143 





Season of 1920: 



Acala (upland) 



29.8±1.4 







