60 



The Journal of Heredity 



when the Department of Agriculture 

 suppHed seed of the Yuma variety to 

 farmers in the Salt River Valle>' and 

 some 200 acres were ])lanted. From this 

 small bcj^inninjj; the industry expanded 

 until in 1917, in the Salt River Valley 

 alone, about 2vS,000 acres of Viuna cotton 

 and about 7,000 acres of Pima cotton 

 were grown and the value to the farmers 

 of the fiber and seed ])ro(luced was esti- 

 mated at about $5 ,000,000 (Frontispiece) . 

 The prospects are that in 1918 not 

 less than 100,000 acres will l)e planted 

 to this crop.^ 



The fiber of both the Yuma and Pima 

 \-arieties has found much favor with 

 American spinners, the automobile tire 

 manufacturers having shown especial 

 interest in this product. The Pima 

 variety, being preferred because of its 

 earliness and its longer fiber, will pro- 

 bably soon completely replace the Yuma. 



HOW TO MAINTAIN UNIFORMITY 



Although the Yuma variety was very 

 uniform at the outset, as now commer- 

 cially grown in Arizona it comprises 

 numerous forms which differ markedly 

 from the original type and which "come 

 true ' ' when self-pollinated. This diver- 

 sity is undoul)tedly due to the fact that 

 the original progeny row was not pro- 

 tected from cross ]X)llination with other 

 types. The seed which was subsequently 

 supplied to farmers for commercial plant- 

 ing was the increase from this row, and 

 although the markedly off type plants 

 had been "rogued" from the seed in- 

 crease fields, the stock was by no means 

 as i)ure as several generations of line- 

 breeding would have made it. Subse- 

 quent experience has shown that a high 

 degree of uniformity can be maintained 

 in the Yuma variety when the latter 

 method is followed. 



The Pima variety, having been 

 strictly line-bred and having been kept 

 effectively isolated, has remained uni- 

 forni. Proof of this was obtained in 

 roguing the seed increase fields dvu'ing 

 the past three seasons. Although more 



than two million plants were examined, 

 not a single ^'ariant was detected which 

 could be compared, in the magnitude of 

 its departure from the type, with the 

 parent jalants of the Yuma and Pima 

 varieties. 



FARMERS COOPERATING 



A cooperative association of cotton 

 growers in the Salt River Valley, 

 assisted by the Department of Agricul- 

 ture, is strenuously endeavoring to 

 maintain the purity of the Pima variety 

 by isolation of the seed increase fields 

 and by separate ginning. Since it has 

 never been ])roven that a stock of cotton. 

 if free from hybrids at the outset, will 

 "run out" white as it is protected 

 from crossing with other sorts, there is 

 good reason to expect that deterioration 

 of this valuable variety can be indefi- 

 nitely postponed. 



ORIGIN BY MUTATION 



The mutational origin of the four 

 varieties of Egyptian cotton which ha\'e 

 been developed in Arizona is indicated 

 by the following facts. Each variety 

 was derived from a single plant which 

 appeared suddenly and differed con- 

 spicuously in several characters from the 

 parent stock. Intennediate forms were 

 not observed. The progenies of these 

 ])lants remained unifoim in their expres- 

 sion of the new characters, so long as 

 cross-pollination with other forms was 

 prevented. 



Origin by mutation seems also to be 

 fairly well established in the case of the 

 nuinerous \-arieties which have arisen 

 from time to time in Iigypt, although 

 the records are less complete than those 

 of the Arizona varieties. Four varieties 

 of comparatively recent origin, Abbassi, 

 Yannovitch, Nubari, and Sakcllaridis. 

 are each reported to have been derived 

 from a single plant selection in a field 

 of Mit Afifi. All of these varieties aji- 

 pcav to have been relatively uniform 

 when first grown, but have rapidl\' 

 deteriorated through cross jxillination 



» For a more complete account of the development of« the' Egyptian cotton industry in Arizona 

 the reader is referred to U. S. Department of Agriculture Bulletin 332 (1916), entitled Community 

 Production of Egyptian Cotton in the United States. 



