54 



BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



Table 32. — Fertilization of unemasculated Pima flowers of which the upper por- 

 tion of the stigmas was thoroughly pollinated with pollen of the same variety, 

 some of the flowers having been inclosed in paper bags and others having 

 been uninclosed. 



Treatment. 



Flowers 

 treated. 



of bolls 

 matured. 



Mean num- 

 ber of seeds 

 per boll. 



Bagged 



Not bagged 



Difference . 



170 

 170 



88.3±1.7 

 89.4±1.6 



17. 2± 0.16 

 17. 0± .19 



1.1±2.3 



.2± .25 



Since the absence of cross-pollination and the environment created 

 by inclosure in bags do not seem to be responsible for the inferior 

 fertilization of the bagged flowers, the third variable, locus of pollen 

 deposition, remains to be considered. Table 33 gives the data of 

 several experiments in which the results of pollinating only the lower 

 halves of the stigmas, as in the case when the flower is bagged and left, 

 to automatic self-deposition, are compared with the results of polli- 

 nating the whole stigmatic surface. In all of these experiments the 

 area of pollen deposition was the only variable, all flowers having 

 been inclosed in bags but not emasculated, and the artificial pollina- 

 tion of the upper portion of the stigmas having been done either with 

 pollen from the anthers of the same flower (experiments of 1916, 

 1917, and 1920) or with pollen from another flower on the same plant 

 (experiment of 1921). 



Table 33. — Relative completeness of fertilization of Pima flowers in which 

 pollen was confined to the lower halves of the stigmas and of flowers which 

 received pollen on the whole stigmatic surface. 



Year and area pol- 

 linated. 



Flow- 

 ers 



treat- 

 ed. 



Percentage 

 of bolls ma- 

 tured. 



Mean num- 

 ber of seeds 

 per boll. 



Year and area pol- 

 linated. 



Flow- 

 ers 



treat- 

 ed. 



Percentage 

 of bolls ma- 

 tured. 



Mean num- 

 ber of seeds 

 per boll. 



Season of 1916: 



1,143 

 1,100 



35.5±1.0 

 45.9±1.0 



10. 8± 0.21 

 12. 5± .18 



Season of 1920: 

 Lower 



95 

 97 



84.2±2.5 

 86.6±2.3 



10.7±0.36 



Whole 



Whole 



11. 2± .32 





Difference 









10.4±1.4 



1.7± .28 





2.4±3.4 



.5± .48 



Season of 1917: 



„ 



Season of 1921: 

 Lower 







78 



90.0±2.3 

 74.0±3.2 



16. 7± .40 

 17. 5± .39 



137 

 176 



94.2±1.4 i 15. 4± .30 

 90.4±1.5 | 17. 5± .17 



Whole . Sfi 



Whole 



Difference 





Difference 







16.0±3.9 



.8± .56 





3.8±2.0 1 2.1-fe .34 



1 











The data in Table 33 show that there was in every case a higher 

 mean number of seeds per boll from flowers of which the whole 

 stigmatic surface was pollinated, although the differences were sig- 

 nificant only in the experiments of 1916 and 1921. These data alone 

 do not make it clear whether the inferior fertilization when pollen 

 is confined to the lower half of the stigmas is due to the smaller 

 size of the area pollinated or to less favorable conditions for pollen 

 development in the basal region of the stigmas. Keference to Table 

 16 shows, however, that confining pollen to half of the stigmatic area 

 when this was the apical half, did not result in diminished fertiliza- 

 tion as indicated by the mean number of seeds per boll. It may be 

 concluded, therefore, that the inferior fertilization of bagged flow- 



