POLLINATION OF PIMA COTTON IN 



RELATION TO THE YIELD OF 



SEED AND FIBER 



Thomas H. Kearney 

 Bureau of Plant Industry, U. S: Department of Agriculture 



A PAPER in the Journal of 

 Heredity for October, 1918, by 

 Rowland M. Meade, entitled 

 "Beekeeping may increase the cotton 

 crop," published after his untimely 

 death, described experiments with the 

 Durango and Acala Upland varieties of 

 cotton at San Antonio, Texas. The 

 results indicated that when the flpsrers 

 were pollinated more thoroughty than 

 is ordinarily the case under natural 

 conditions at that locality, the bolls 

 contained a greater number of seeds. 

 Meade concluded that "growers of 

 long-stapled varieties might find bee- 

 keeping a distinct advantage to the 

 cotton crop." It is important to know 

 whether the same conclusion holds good 

 with the Eg>^ptian type of cotton, as 

 grown in Arizona. 



description of the cotton flower 



A few words in regard to the struc- 

 ture of the cotton flower are necessary 

 to make clear what follows. The center 

 of the flower is occupied by a long 

 slender organ, the pistil, which ends at 

 the base in a cone-shaped structure 

 called the ovary. If the ovary is cut 

 open it is found to contain numerous 

 small white bodies, the ovules. The 

 greater part of the length of the pistil 

 is enclosed by a thin sheath which 

 bears numerous stamens, the organs 

 which contain the pollen. The grains 

 of pollen, falling upon the portion of 

 the pistil which projects above the top 

 of the sheath, germinate and send out 

 slender tubes which grow down through 

 the pistil until they reach the ovules. 

 When a pollen tube comes into contact 

 with an ovule, fertilization takes place 

 and the fertilized ovule develops into a 

 seed while the container, the ovary, 

 increases in size and becomes the boll. 



Examination of the Egyptian cotton 

 flower shows that the white pistil ex- 

 tends far above the column of bright 

 yellow stamens (see Frontispiece). If a 

 flower is enclosed in a paper bag, so 

 that insects are kept out, it will be 

 found that the pollen, which looks to 

 ith« naked eye like golden dust, is 

 deposited only upon the part of the 

 pistil which is just outside the sheath 

 and is surrounded by the upper sta- 

 mens. The club-shaped summit of the 

 pistil receives pollen only when it is 

 carried there by insects. Observation 

 has shown that the cross pollination of 

 cotton flowers is accomplished chiefly 

 by bees and wasps. The honey bee 

 is often very efficient as a pollinator 

 but sometimes prefers to work on the 

 nectaries outside the flower rather than 

 within the blossom. 



INSECTS abundant ONLY IN SOME 

 LOCALITIES 



At Sacaton, on the Pima Indian 

 reservation in southern Arizona, where 

 such insects are abundant, the entire 

 free surface of the pistil is usually found 

 to be thickly coated with pollen soon 

 after the flower opens in the morning. 

 But in the heart of the cotton growing 

 district of the Salt River Valley, at 

 distances of 25 to 40 miles from Saca- 

 ton, numerous observations in 1919 and 

 1920 showed that pollination is much 

 less complete. Even late in the after- 

 noon the tops of the pistils are often as 

 white and as free from pollen as when 

 the flowers are bagged to insure self- 

 fertilization. Visits to fields on the 

 outskirts of the Valley, at Litchfield 

 and at Goodyear, on the contrary, 

 showed the flowers to be as well polli- 

 nated as at Sacaton. The difference in 

 these several localities is doubtless due 



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