- 13 - 
Kearney, T. H. 
1923. Self-fertilization and cross-fertilization in Pima cotton. U.S. 
Dept. Agr. Dept. Bui. 1134, 68 pp. 
p. 49: Observation in Arizona has shown that the number of 
efficient pollinating insects differs greatly in different localities. 2/ 
Bees and other active pollinators are normally abundant among the 
cotton Flowers at Sacaton throughout the summer, and the entire surface 
of the stigmas is almost invariably well covered with pollen soon 
after the corolla has opened. On the other hand, observations in the 
Salt River Valley, at distances of 25 to 40 miles from Sacaton, have 
shown that insect pollination of cotton there is often much less rapid 
• and complete. The probable explanation is that in recent years an 
extensive and almost continuous acreage has bsen planted to cotton, and 
the insect population is not large enough to insure thorough pollin- 
ation of- all the flowers. 
Thus, en July 13, 1919, in a field situated near Tempe in the 
heart of the cotton-growing district, no pollen grains were observed 
upon the extrastaminal portion of the stigmas at 9 a.m. and very few 
at 10 a.m. Late in the afternoon of July 20, 1920, inspection of the 
- same field showed- the extrastaminal portion of the stigmas to be 
free from pollen in most of the flowers, while the remaining bore only 
a few insect-transported grains. None of the flowers examined showed 
thorough pollination of the whole stigmatic surface.- Two other cen- 
trally located fields, one at Phoenix and one near Tempe, which were 
examined at 5 p.m. on August 5 and at 4 p.m. on August 6, showed 
similarly deficient pollination. On the other hand, in fields situated 
on the outskirts of the valley, at Litchfield and at Goodyear, which 
were examined at noon on the same days, bees and other pollinators 
were abundant, and the stigmas of the cotton flowers were found to be 
well covered with pollen, 
p. 50: In the mean number of seeds per 100 flowers, a value 
which integrates the percentage of bolls matured and the mean number 
of seeds per boll, the increase due to artificial pollination amounted 
to 32 per cent, indicating t hat a substant ial ly great e r crop both of 
s 2_: af fiber m igh t be expected jf_be es w ere abundant in the Salt 
R iver Valley cotton fields during the blossoming period . 
2/ A pronounced difference in the abundance of pollinating insects 
at different localities in Arizona was noted by Cook, McLachlan, and Meade. 
"At the tj ce of our visits to the fields at Yuma and Sacaton there 
notable difference in the activity of the insects at the two places, Several 
species of large .re industriously visiting the flowers at 
Yuma in September were not seen at all at Sacaton." 
