30 



BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



flower buds were emasculated the evening before anthesis, other buds 

 having been bagged at the same time to supply pollen. On the fol- 

 lowing morning approximately equal numbers of the emasculated 

 flowers were pollinated (1) near the apex of the stigmas, (2) near 

 the base, and (3) on the whole stigma tic surface. Record was kept 

 of the number of bolls which matured from the several treatments 

 and of the number of seeds in each boll, from which were computed 

 the data given in Table 16. 



Table 16. — Degrees of fertilization in Pima cotton resulting from pollination of 

 the apical and of the basal portion of the stigmas and of the whole stigmatic 

 surface. 



Locus of pollination. 



Flowers 

 treated. 



Percentage 

 of bolls 

 matured. 



number of 



seeds per 



boll. 



Near the apex of the stigmas 



Near the base of the stigmas 



Upon the whole length of the stigmas 



94 



98 

 100 



80.8±2.73 

 89.8±2.04 

 98. 0± .94 



14.7±0.28 

 9.7± .29 

 14. 1± .22 



A higher percentage of bolls matured from flowers pollinated near 

 the base of the stigmas than from flowers pollinated near the apex, 

 but the difference is not significant. On the other hand, the mean 

 number of seeds per boll resulting from basal pollination was much 

 smaller than that resulting from apical pollination, the difference 

 having been 5.0±0.40 (more than 12 times its probable error). 

 Pollination of the whole stigmatic surface yielded a significantly 

 higher percentage of bolls matured than did either partial pollina- 

 tion, but did not show a significant difference in the mean number 

 of seeds per boll as compared with pollination of the apical portion 

 only. It may be inferred from this fact that a difference between 

 the two halves of the stigmas is responsible for the inferior fertiliza- 

 tion from basally deposited pollen, the extent of the area receiving 

 pollen having been approximately the same in the apical and basal 

 pollinations. 



The data given in Tables 15 and 16 indicate 17 that when flowers of 

 Pima cotton are emasculated and are pollinated artificially the basal 

 region of the stigmas is a less favorable medium for the germination 

 or development of pollen than is the apical region. 18 Care was taken 

 in these experiments to apply as nearly as practicable equal quan- 

 tities of pollen at both loci, but it was noted that the pollen adhered 

 more closely to the stigmatic surface when apically deposited than 

 when basally deposited. This was probably a factor in the superior 

 fertilization from apical pollination. It is doubtful, however, 

 whether this factor is operative in equal degree under natural con- 

 ditions, for, with the stamens present, the close contact of the upper 



17 Additional and conclusive evidence th^t when emasculated flowers of Tima cotton 

 are pollinated artificially better fertilization results with apical than with basal deposi- 

 tion of the pollen was obtained from two experiments in 1922, the compete data of 

 which were not available in time to be included in this bulletin. 



18 Meade HO, p. 282) concluded from the results of his investigation of pollination in 

 upland cottons, referred to under the heading " Structure of the flower in relation to 

 pollination," that " most of the flowers with long stigmas projecting above the stamens 

 do not become completely self-fertilized, as the anthers and stigmas are too widely 

 separated." If limitation of pollen deposition to the basal region, as would be the case 

 in flowers having long stigmas when pollinating insects are scarce, results generally in 

 inferior fertilization, Meade's conclusion is probably well founded. 



