FERTILIZATION IN PIMA COTTON. 



41 



type, the differences having been, respectively, six and four times 

 the probable error. This outcome being somewhat unexpected the 

 experiment was repeated in 1921. Five plants of an inbred (seven 

 generations selfed) Pima family were used as mothers. Flowers were 

 emasculated before anthesis and were cross-pollinated the following 

 day, some with pollen from plants of the bulk Pima stock, others 

 with pollen of Acala (upland). The flowers which received both 

 pollinations were borne on the same plants. The results of this ex- 

 periment are also presented in Table 23 (lower part). 



Table 23. — Fertilization of emasculated Pima flowers, some of which were 

 cross-pollinated with pollen of the same variety and others with pollen of the 

 Acala variety of upland cotton in 1920 and 1921. 



Season and character of pollination. 



Flowers 

 treated. 



Percent- 

 age of 

 bolls 



matured. 



Mean 

 number 

 of seeds 

 per boll. 



Mean 

 weight of 

 100 seeds 

 (grams). 



Percent- 

 age of 



germina- 

 tion, 



Season of 1920: 



Pima pollen 



45 



48 



80.0±4.0 

 79.2±3.9 



12. 9± 0.45 

 16. 2± .29 



12. 5± 0.26 

 12. 6± .08 



92.5±0.9 



Acala (upland) pollen 



96. 6± .5 







Difference 





.8±5.6 



3.3± .53 



• 1± .27 



4.1±1.0 









Season of 1921: 



Pima pollen 



175 



176 



86.3±1.7 

 93.1±1.3 



17. 5± .18 

 17. 6± .16 



12. 6± .08 

 13. 0± .10 



89. 7± .9 



Acala (upland) pollen 



93. 0± .8 







Difference 





6.8±2.1 



.1± .24 



.4± .13 



3.3±1.2 









In 1921 application, of pollen of a different type, Acala, resulted 

 in a slight but possibly significant increase in the percentage of bolls 

 matured, but did not effect more nearly complete fertilization, the 

 mean number of seeds per boll having been practically the same as 

 that obtained by cross-pollination within the variety. There were 

 indications that fertilization by the more foreign pollen slightly 

 increased the weight and percentage germination of the seeds, 

 although the differences were scarcely significant. 



Considering the whole series of experiments in which pollens of 

 different degrees of foreignness were compared as to their relative 

 efficiency in fertilizing Pima flowers, it may be concluded that fer- 

 tilization by the more foreign pollen is consistently neither better 

 nor poorer than that effected by the more nearly related pollen. The 

 conclusion holds good whether comparison is made (1) between 

 pollen of the same plant or of a sister plant of an inbred family 

 and pollen of unrelated plants of the same variety, or (2) between 

 pollen of the same variety and pollen of another variety of the same 

 type of cotton (Gila, Egyptian). On the other hand, comparison 



* Two experiments performed in 1922, the detailed results of which were not available 

 in time to be included in this bulletin, showed that bolls from Pima flowers pollinated 

 with upland pollen (Lone Star variety) as compared with bolls from Pima flowers 

 pollinated with Pima pollen, contained significantly greater mean numbers of seeds, the 

 increases from extra- varietal pollination, in the two experiments, respectively, having 

 been 9 and 15 per cent and having been 4.5 and 4.4 times the probable error of the 

 difference. The .reciprocal pollinations on Lone Star (upland), on the contrary, gave 

 in both experiments a greater mean number of seeds per boll from the flowers pollinated 

 with Lone Star pollen than from the flowers pollinated with Pima pollen, the decreases 

 from extra-varietal pollination of Lone Star in the two experiments having been, re- 

 spectively, 19.3 and 5.4 per cent, although the decrease was barely significant in the 

 first experiment (difference 3.2 times its probable error) and was not significant in the 

 second experiment. These results might be taken as indicating superior vigor of the 

 Lone Star pollen but, when the two pollens were tested in sugar solution, the Pima 

 pollen ejected somewhat more raoidly and completely than the Lone Star pollen. 



