FERTILIZATION IN PIMA COTTON. 



53 



THE INFERIOR FERTILIZATION OF BAGGED FLOWERS. 



Bolls from flowers which have been inclosed in paper bags in 

 order to prevent cross-pollination and which have not been pollinated 

 by hand nearly always contain fewer seeds than bolls from open- 

 pollinated flowers. For example, in 1915, the mean number of seeds 

 per boll in 678 bolls from bagged flowers was found to be only 

 13.6 ±0.34, as compared with a mean of 16 ±0.12 in 530 bolls from 

 open-pollinated flowers. In Table 31 are assembled the data from 

 a number of experiments which afforded a close comparison of the 

 relative fertilization of bagged and of open-pollinated flowers, both 

 lots of flowers having opened during the same period and either on 

 the same or on neighboring plants. 



Table 31. 



-Relative completeness of fertilization in lagged and in open- 

 pollinated flowers of Pima cotton. 



Year and treatment of flower. 



Num- ! Mean num- 

 ber of I ber of seeds 

 bolls. per boll. 



1 



Year and treatment of flower. 



Num- 

 ber of 

 bolls. 



Mean num- 

 ber of seeds 

 per boll. 



Season of 1916: 



743 

 707 



10.9±0.14 

 15. 3± .12 



Season of 1920: 



80 

 95 



10. 7 ±0.36 







14. 2± .21 











4.4± .18 



3.5± .42 





168 

 174 



B agged 



634 



360 





Season of 1919: 



13. 9± .23 

 16. 6± .25 



il.5± .13 







15.9± .11 











4.4± . 17 





2.7± .34 



Season of 1921: 



Bagged 



129 

 560 







62 



58 







16. 5± .25 

 18. 2± .22 



15. 4± .30 



Open pollinated 



Open pollinated 



17. 3± .09 





Difference 





Difference 



1.7± .33 



1.9± .31 













The data in Table 31 indicate in every case very significant in- 

 feriority of the bagged flowers in relative completeness of fertiliza- 

 tion. In seeking an explanation of this difference the following 

 factors are to be considered : 



(1) Exclusive self-pollination of the bagged flowers. 



(2) Special environment created by inclosure of the flowers, in paper bags. 



(3) Pollination of only the lower half of the stigmatic surface in the bagged 

 flowers. 



Evidence was given on a preceding page that in Pima cotton self- 

 pollination as compared with cross-pollination does not result in an 

 inferior degree of fertilization. That inclosure of the flowers is not 

 an important factor is indicated by the results of an experiment in 

 1921. On the same Pima plants a number of flowers were bagged be- 

 fore opening, and others were left unbagged. Neither lot was emas- 

 culated, and both were pollinated during the morning of the day of 

 anthesis with pollen from other plants of the same variety, the whole 

 stigmatic surface having been thoroughly covered with pollen. Pres- 

 ence or absence of the bags was therefore the only variable. The data 

 given in Table 32 show that the bagged flowers were as well fertilized 

 as those which were not inclosed. 



