46 BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



The difference in the percentage of hybrids produced in 1919 by the 

 two foreign pollens was not significant, and it is clear that pollen of 

 another variety of the same species (Egyptian cotton) was not 

 better able than pollen of a different species (upland cotton) to 

 compete with the self pollen. The percentage of hybrids in both 

 cases is very high in comparison with that of the 1916 experi- 

 ment with Gila pollen. • 



In a similar experiment in 1920 a number of Pima flower buds 

 were bagged but were not emasculated, so that automatic self- 

 pollination was not interfered with. Early in the afternoon of the 

 day of anthesis abundant pollen of the Acala variety of upland 

 cotton was applied to the stigmas. The resulting seed was planted 

 in 1921. No thinning was done, all seeds which germinated having 

 been allowed to develop. The resulting percentage of F 1 hybrids, 

 as also stated in Table 26, did not differ significantly from that 

 yielded by seed resulting from the corresponding self -f- cross- 

 pollination in the experiment of 1919. 



The percentage of cross-fertilization in all three of these experi- 

 ments was considerable, notwithstanding that both in time of arrival 

 upon the stigmas and in nearness to the ovary the automatically 

 deposited self pollen would seem to have had a marked advantage. 

 The results therefore tend to confirm the evidence given on pre- 

 ceding pages that conditions at the base of the stigmas are rela- 

 tively unfavorable for the germination of the pollen or penetration 

 of the tubes. 



DEPOSITION OF THE TWO POLLENS SIMULTANEOUS. 



An experiment performed in 1919 was designed to determine what 

 percentages of the ovules are fertilized by pollen of the same and 

 of another variety when both sorts of pollen are applied as nearly 

 as possible simultaneously and in as nearly as possible equal quan- 

 tity.^ For this purpose a number of Pima cotton flowers were 

 emasculated and bagged in the evening. During the following 

 morning the stigmas were smeared with pollen of the same variety 

 and with pollen of Acala (upland) cotton. Half of the flowers on 

 each date received the upland pollen first, and the other half received 

 the Pima pollen first, but the interval of time between the applica- 

 tions of the two lots of pollen was negligible. This method of apply- 

 ing the two pollens was adopted because of the impracticability of 

 mixing them in approximately equal quantity. The comparative 

 viability of the pollens used in this experiment was not determined, 

 but pollen of Pima and of Acala from plants growing in the same 

 field had been tested in a sugar solution three weeks previously and 

 had shown no appreciable difference in viability. 



The seeds obtained from each pollination were planted in 1920, 

 four seeds to the hill, and the rows were not thinned. The number 

 of first-generation Egyptian X upland hybrids in each lot was 

 determined early in July, with the results given in Table 27. Com- 

 parison of the percentages of hybrids in hills containing, respec- 

 tively, one, two, three, and four plants, showed no significant differ- 

 ences. This would indicate that the heterozygotes, in spite of the 

 larger size which they soon attained, had had no special advantage 

 during the germinating and seedling stages (see p. 5). 



