UNITED STATES DEPARTMENT OF AGRICULTURE 



DEPARTMENT BULLETIN No. 1134 



Washington, D. C. 



PROFESSIONAL PAPER 



April 26, 1923 



SELF-FERTILIZATION AND CROSS-FERTILIZATION IN PIMA COTTON. 



By Thomas H. Kearney, Physiologist in Charge of Alkali and Drought Re- 

 sistant Plant Investigations, Bureau of Plant Industry. 



CONTENTS. 



Page. 



Introduction 1 



Vicinism, or natural hybridization, 



in cotton 2 



Structure of the flower in relation 



to pollination 12 



Ontogeny of the flower in relation 



to pollination 16 



Locus of pollen deposition in rela- 

 tion to self-fertilization and cross- 

 fertilization 27 



Relative earliness of arrival of self- 

 deposited and of insect-carried 

 pollen 31 



Deposition of self pollen and of for- 

 eign pollen by insects 34 



Pollen-carrying insects at Sacaton__ 36 



Page. 



Relative compatibility of like and of 



unlike pollen 38 



Pollen competition as a factor in 

 self-fertilization and cross-fertili- 

 zation 42 



Relative completeness of insect polli- 

 nation at different localities 49 



Seasonal variations in relative com- 

 pleteness of fertilization 51 



The inferior fertilization of bagged 



flowers 53 



Boll shedding in relation to pollina- 

 tion and fertilization _: 55 



Inbreeding in relation to fertility- _ 56 



Summary 61 



Literature cited 66 



INTRODUCTION. 



The three principal types of cotton grown in the United States — 

 upland (Gossypium hirsutum), sea island (G. barbadense) and 

 Egyptian 1 — hybridize freely among themselves when opportunity 

 is afforded for cross-pollination. The first or conjugate generation 

 of the hybrid between any two of these types is extremely fertile 

 and vigorous, but in hybrids of upland with sea-island or with 

 Egyptian cotton degenerate and more or less sterile forms occur 

 in large numbers in the later generations (29). 2 On the other hand, 

 so far as is known, the per jugate generations of crosses between 

 varieties of the same type are little, if any, inferior in fertility to the 

 parents. The high degree of compatibility between types so dis- 

 tinct as Egyptian and upland makes the frequency of natural cross- 

 fertilization under given conditions a problem of much importance 

 in breeding work with this plant and in maintaining supplies of 

 pure seed of the agricultural varieties. 



1 The Egyptian type of cotton as it now exists appears to constitute a distinct botanical 

 species, although it is supposed to have originated through hvbridization (27, p. 289). 



f Serial numbers (italic) in parentheses refer to "Literature cited" at the end of 

 this bulletin. 



22421—23 1 



