FERTILIZATION IN PIMA COTTON. 



57 



percentage of ovules which failed to develop into seeds was no 

 greater in the continuously self- fertilized than in the continuously 

 open-pollinated population. Kottur states further that continuous 

 self-fertilization in the Asiatic cottons (Gossypium herbaceum and 

 G. neglectum) and in American upland cotton (G. hirsutum) did 

 not induce sterility. 



The effects of inbreeding in Pima cotton have been the subject of 

 investigation at Sacaton, Ariz., the following criteria of fertility hav- 

 ing been considered : 



Viability of the pollen. 



Number of ovules. 



Rate of flowering. 



Boll-shedding percentage. 



Size of the boll. 



Weight of seed cotton per bolL 



Number of seeds per boll. 



Weight of seeds. 



Viability of the seeds (germination percentage). 



Lint index (weight of fiber per 100 seeds). 



Comparison with random samples of the continuously open-polli- 

 nated (hence, more or less cross-pollinated) stock has been used neces- 

 sarily as the measure of fertility in the inbred populations, although 

 it is realized that inbreeding may have been accompanied by segre- 

 gation, plus or minus, in respect to some or all of these values. There 

 was, however, no intentional selection in the development of the 

 inbred families here dealt with. 



POLLEN VIABILITY Or AN INBRED POPULATION. 



A family resulting from strict self-fertilization during five suc- 

 cessive generations was compared in 1919 with a continuously open- 

 pollinated stock in regard to the viability of the pollen as measured 

 by the rate of ejection of the contents of the grains and by the 

 percentage of the total number ejected in a 5 per cent solution of 

 cane sugar (see p. 22). Flowers were collected at 11 a. m., one 

 from each of five plants in each population, and flowers of the 

 inbred and of the open-pollinated stock were alternated in making the 

 tests. The results, as given in Table 35, show no difference in the 

 average viability of the pollen. 



Table 35. — Viability of the pollen from plants of a family of Pima cotton inbred 

 during five generations compared toith that from plants of a continuously 

 open-pollinated stock of this variety. 



Plant and flower. 



Inbred family. 



After Immersion j 

 until ejection— _ .. 

 | Esti- 

 — ; j mated 



Beean I Ceas * d eJeCti0n ' 

 Began. , actively# i 



j i 



Open-pollinated stock. 



After immersion 

 until ejection— 



T, orran Ceased 

 Be S an - j actively. 



Esti- 

 mated 

 ejection. 



Seconds. 



No. 1 70 



No. 2 65 



No. 3 70 



No. 4 i 85 



No. 5 ■ i 55 



Average 69 



Seconds. ' Per cent. 

 170 95 



110 100 



180 100 



155 93 



120 i 100 



Seconds. Seconds. 

 60 

 60 

 70 

 65 i 



65 



Percent. 

 170 95 

 170 100 

 135 i 95 

 120 100 

 140 100 



147 



147 



