FERTILIZATION IN PIMA COTTON. 47 



Table 27. — Hybrids from seeds produced by emasculated flowers of Pima cotton 

 when pollinated first with upland cotton and then with Pima pollen and vice 

 versa. 





Pollination. 



Plants. 



Fi hybrids. 





1 Number. 



Per cent. 



Pirua X upland -f Pima. . . 





134 



1 ! 



33 j 

 21 



24.6±2.5 







160 



13.1-*-1.8 











As one array 



! 294 



i "1 



18.4±1.5 







I 





It will be noted that the percentage of hybrids produced was 

 almost twice as great when the upland pollen was applied first as 

 when the Pima pollen was applied first, and the difference amounted 

 to about three and a half times its probable error, whereas in the 

 double-pollination experiment performed by McLachlan (Table 25) 

 the percentage of hybrids from flowers borne by Egyptian plants was 

 somewhat higher when Egyptian pollen was applied first than when 

 upland pollen was applied first. Possibly in the present experiment 

 the stigmas were so well covered at the first application that many of 

 the pollen grains of the second application were not in contact with 

 the stigmatic surface. It would seem to be a fair assumption that 

 the percentage of hybrids obtained by taking as one array plants re- 

 sulting from the two treatments represents what would have been 

 obtained if a mixture of both pollens in equal quantity had been 

 applied. 



The results of the McLachlan experiment showed that 89 per $ent 

 of the ovules of Yuma (Egyptian) cotton had been fertilized by pol- 

 len of the same variety when upland pollen w T as also present on 

 the stigmas. In the present experiment 82 per cent of the ovules of 

 Pima (Egyptian) cotton were fertilized by pollen of the same va- 

 riety, although both pollens were applied as nearly as possible simul- 

 taneously and in equal quantity. The fact that even when upland 

 pollen was applied first only about 25 per cent of the resulting plants 

 were hybrids makes it difficult to avoid the conclusion that on the 

 stigmas of Egyptian cotton pollen of the same variety is strongly 

 prepotent over upland pollen. 



It is interesting to compare the percentages of hybrids obtained 

 in the double-pollination experiment (Table 27) with the percent-, 

 ages, as given in Table 26 (1919 experiment) , from flowers which had 

 not been emasculated and had had the stigmas pollinated (1) with 

 pollen of another variety of Egyptian cotton and (2) with upland 

 pollen. Notwithstanding the fact that in the latter case automatic 

 self-pollination of the basal or interstamen region of the stigmas was 

 not interfered with, the percentage of hybrids which resulted from 

 either cross-pollination was about twice as great as the average of the 

 percentages from the two double cross-pollinations of emasculated 

 flowers. This further corroborates the conclusion that pollen de- 

 posited at the base of the stigmas, as was the self pollen in the un- 

 emasculated flowers, is under less favorable conditions than pollen 

 deposited nearer the apex, as was the foreign pollen in the same 

 flowers. In the double pollination of emasculated flowers the pollen 

 of both kinds was deposited over the same stigmatic area. 



