22 BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



ever, the anthers often begin to open and to discharge pollen before 

 the petals commence to unfold. It seems clear that even in Pima cot- 

 ton no considerable quantity of pollen ordinarily is deposited upon 

 the stigmas before the expansion of the corolla has begun. 



Other investigators have noted that different species of Gossypium 

 differ in the rate of opening of the anthers. A statement by Fyson 

 (18, p. 5) implies that in India the anthers of American upland 

 cotton (Gossypium hirsutum) open and discharge their pollen earlier 

 than do anthers of Asiatic species (G. herbaeewm, etc.). Smith 

 (U), in the West Indies, observed that sea-island cotton (G. bqr- 

 badense) opens its anthers earlier in the day than does a native 

 cotton of the American upland type. 

 « 



VIABILITY OF THE POLLEN IN DIFFERENT STAGES OF DEVELOPMENT. 



The viability of the pollen during the hours immediately pre- 

 ceding and following the opening of the corolla is of interest in 

 relation to the phenomena of pollination. The rapidity and com- 

 pleteness with which the pollen grains eject their contents at different 

 stages in the ontogeny of the flower were tested by immersing them 

 in a 5 per cent aqueous solution of cane sugar, although apparently 

 ejection takes place with equal readiness in water. 



The discharge of protoplasm by the pollen grain in these media 

 takes place in the manner described as " pseudogermination " by 

 Andronescu (^), the contents being ejected with explosive sudden- 

 ness in a very long slender thread, which immediately becomes 

 twisted into a tangled spiral. Andronescu's illustration of the 

 process in Zea (|, pi. 2) represents very well the phenomenon as it 

 occurs in Gossypium. It is uncertain in what degree the rate of 

 pseudogermination at different hours of the day is correlated with 

 that of normal germination upon the stigmas. It will be shown, 

 however, that in cotton little or no pseudogermination takes place in 

 the evening preceding the opening of the corolla and that it in- 

 creases in rapidity and completeness during the following morning, 

 reaching a maximum intensity at noon and then gradually declining 

 to a very low minimum long before sunset. It seems at least prob- 

 able that normal germination follows a similar course and that the 

 vigor of pseudogermination is indicative of the viability of the 

 pollen (4, p. 16). The phenomenon will be referred to in this bul- 

 letin as "ejection," thus avoiding the cumbersome term "pseudo- 

 germination." 



Observations were made with a binocular microscope. The pollen 

 was immersed in the sugar solution as soon as possible after de- 

 taching the flower from the plant. The criteria of viability used 

 were (1) the number of seconds after immersion until active ejection 

 ceased and (2) the percentage of the total number of grains in the 

 field of the microscope which discharged their protoplasm during 

 the period of active ejection. An "index of viability," which inte- 

 grates rapidity and completeness of ejection at different hours, was 

 obtained by dividing the percentage of the total grains ejected by the 

 number of seconds required to complete active ejection and multi- 

 plying the quotient by 100. 



The condition of the pollen on the day preceding anthesis will be 

 considered first. Pollen from Pima buds was collected on several 



