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



Evidence is presented in this bulletin that although the cotton 

 flower is admirably adapted to cross-pollination most of the ovules 

 usually are self-fertilized. The percentage of vicinists, or natural 

 hybrids, produced when two distinct varieties or types are grown 

 side by side ordinarily is not large, although the occurrence of only 

 a small initial percentage may, of course, seriously impair the purity 

 of the stock. In the Egyptian type of cotton, particularly, self-fer- 

 tilization has been found to predominate greatly over cross-fertiliza- 

 tion. Investigations of the structure and later ontogeny of the 

 flower, of the deposition of self pollen and of foreign pollen upon 

 the stigmas, and of _ the competition of like and unlike pollens, 

 here described, contribute to an explanation of the predominance 

 of self-fertilization. Other aspects of the subject treated are the 

 local and seasonal differences in the relative completeness of fertiliza- 

 tion and the effect upon fertility of continued self-fertilization. 



Most of the data and conclusions relate to the Pima variety of the 

 Egyptian type of cotton, but comparison with upland cotton has 

 been made in numerous instances. With very few exceptions the 

 experiments were performed at Sacaton at the Pima Indian Agency 

 in southern Arizona during the eight-year period from 1914 to 

 1921. Acknowledgment is made of the cordial cooperation of 

 S. H. Hastings, formerly superintendent of the Cooperative Testing 

 Garden at Sacaton, and of C. J. King, the present superintendent. 



Many of the experiments from 1914 to 1919, inclusive, were per- 

 formed by Walton G. Wells, during that period assistant cotton 

 breeder in the Office of Alkali and Drought Resistant Plant Investi- 

 gations, Bureau of Plant Industry. Walter F. Gilpin, assistant 

 cotton breeder in the same office, who assisted in the work during 

 1917 and 1919, performed many of the experiments during the years 

 1920 and 1921. Others who have aided in the investigations are 

 H. G. McKeever, Rolla B. Wade, Harvey Thackery, F. Ben Clark, 

 Roy W. Nixon, George C. Powell, George J. Harrison, Robert D. 

 Martin, C. J. King, W. W. Ballard, Max Willett, R. H. Manthey, 

 R. H. Peebles, and C. A. Bewick. 



Plates I, II, III, IV, and V are from photographs by W. F. Gilpin. 

 Plates VI and VTI are from photographs by Harold F. Loomis, of 

 the Office of Crop Acclimatization and Adaptation Investigations, 

 Bureau of Plant Industry. 



VICINISM, OR NATURAL HYBRIDIZATION, IN COTTON. 



In considering the evidence regarding the occurrence of vicinists, 

 or natural hybrids, the published results of other investigators will 

 be reviewed, and the data of experiments performed in Arizona will 

 be presented. 



DATA ON VICINISM IN LITERATURE. 8 



Webber, as the result of his experience in South Carolina and 

 other Southeastern States, observes (48, p. 370) : 



In several instances varieties have been grown in single rows with other 

 varieties all around them of such a kind that crossing where it occurred could 

 be easily detected in the progeny. Plants grown from seed matured under 



• The accounts of experiments concerning vicinism in cotton rarely state whether or not 

 the rows were thinned ; and, if so, whether the removal of the extra plants was managed 

 so as to avoid discrimination in favor of the more vigorous hybrid individuals. 



