26 



BULLETIN 1134, TJ. S. DEPARTMENT OF AGRICULTURE. 



Table 12. — Comparison of morning and evening pollination of cotton flowers, 

 showing the percentage of boUs matured and the mean number of seeds 

 per boll. 



Time of pollination. 



Flowers pollinated at 8 a. m. 

 Flowers pollinated at 5 p. m. 



Flowers 

 treated. 



Difference . 



120 

 120 



Percentage 



of bolls 



matured. 



89.2±1.93 



95. 0±1. 35 



number of 



seeds per 



bolh 



14. 5± 0.23 

 13. 4± .28 



5.8±2.35 i 1.1± .35 



Another experiment was performed in 1921 with the object of 

 ascertaining whether the pollen in bagged flowers remains viable as 

 long as 26 hours after anthesis would have begun under normal 

 conditions. Pima flower buds were emasculated in the evening of 

 August 5 and pollinated on August 6. Of the 100 buds emasculated 

 50 were pollinated at 1 p. m. with pollen from flowers which had 

 been bagged on August 5 at the time the emasculation was done. The 

 other 50 were pollinated at 9 a. m. with pollen from flowers bagged 

 in the bud on August 4 which at the time of pollination were about 

 26 hours past the normal time of the beginning of anthesis. In these 

 old flowers when collected for use in pollination, the petals were 

 wilted and the pollen was very loose in the anthers. The relative 

 fertilization obtained from the two pollinations, as shown in Table 

 13, indicates that although the flowers had been protected by En- 

 closure in bags, much of the pollen had lost its ability to effect fer- 

 tilization 26 hours after the normal time of the beginning of anthesis. 



Table 13. — Results obtained by pollination with old and with fresh pollen, 

 showing the percentage of bolls matured and the mean number of seeds per 

 boll. 



Pollination with, pollen from flowers in which anthesis normally would : Flowers 

 have begun— treated. 



boU. 



i matured. 



6 hours previously (fresh pollen) . 

 26 hours previously (old pollen). 



85.7±3.44 

 38.0±4.63 



12. 6± 0.41 

 6.4± .58 



DURATION OF THE RECEPTIVITY OF THE STIGMAS. 



It has been mentioned that in uninclosed cotton flowers at Saca- 

 ton, Ariz., the stigmas show a perceptible loss of turgor before 

 sunset of the day of anthesis. The results of the experiment sum- 

 marized in Table 12 indicate, however, that when the flowers have 

 been protected by bagging, the stigmas show no appreciable loss 

 of receptivity, as measured by the degree of fertilization attainable, 

 as late as 5 p. m. In order to determine whether the stigmas retain 

 their receptivity for a still longer period when the flowers are in- 

 closed, 100 Pima flower buds were emasculated and bagged during 

 the evening of August 3, 1921, and were cross-pollinated with fresh 

 pollen from Pima plants, half of them at 1 p. m. of the day fol- 

 lowing emasculation and half at 8 a. m. of the second day. It 

 proved somewhat difficult to extract pollen from the anthers of the 



