heritable variations in an apparently 
UNIFORM VARIETY OF COTTON 
By Thomas H. Kearney 1 
Physiologist in Charge , Office of Alkali and Drought Resistant Plant Investigations , 
Bureau of Plant Industry , United States Department of Agriculture 
The Pima variety of American Egyptian cotton, which originated with 
a single plant selection in 1910 and of which approximately 100,000 bales 
were produced in 1920, is probably the least variable of commercially 
grown cottons. So great, indeed, is the apparent uniformity that one 
might question the utility of further selection within the variety and of 
roguing seed-increase fields which are not exposed to accidental contami¬ 
nation. The justification of these procedures rests upon proof that 
heritable variations are not infrequent, and the object of this paper 
is to examine the evidence of their occurrence. 
It is possible to measure the results of selection in the Pima variety 
because, fortunately, some of the seed produced by the parent plant of 
1910 had been preserved. When plants grown from this seed in 1919 
were compared with the present commercial stock and with a line-bred 
strain it was found that although there has been no definite change of 
type the modes for certain characters have been altered by selection. 
Additional evidence of the occurrence of slight but heritable variations 
has been obtained in the course of the breeding and roguing work. A 
much wider variation, outside the normal range of the Pima variety 
but not attributable to recent hybridization, has also proved to be 
heritable. 
EARLY HISTORY OF THE PIMA VARIETY 
The Pima variety originated with a plant discovered at Sacaton, Ariz., 
in 1910, in a field of the Yuma variety. The Yuma variety likewise 
originated with a single plant discovered at Yuma, Ariz., in 1907 in a 
stock of the Mit Afifi variety which had been introduced from Egypt 
several years previously. The parent plants of both the Yuma and 
Pima varieties were so different from the stocks in which they appeared 
and their progenies expressed the new characters so uniformly that their 
origin was attributed to mutation. 2 
1 The writer is indebted to Messrs. Walter F. Gilpin and Robert L. Taylor for the photographs used in 
illustrating this paper. 
2 Kearney, Thomas H. mutation in Egyptian cotton. In Jour. Agr. Research, v. 2, no. 4, p. 287- 
302, pi. 17-25. 1914. literature cited, pp. 301-302. 
- A plant industry based upon mutation ... In Jour. Heredity, v. 9, no. 2, p. 51-61, 8 fig. 
1918. 
-and Wells, Walton G. a study op hybrids in Egyptian cotton. In Amer. Nat., v. 52, no. 
622/623, p. 491-506, 3 fig. 1918. Literature cited, p. 506. 
Journal of Agricultural Reseat ch, 
Washington, D. C. 
xu 
Vol. XXI, No. 4 
May 16, 1921 
Key No. G-231 
