28 FIELD CROPS FOR THE COTTON-BELT 



the stigmas well above the stamens, so that insects may 

 be required for fertilization. In flowers of American 

 upland cotton the style is usually shorter and the stigmas 

 may remain buried aiiiong the stamens, insuring self- 

 fertilization.^ 



30. The pollen-grains and egg-cells. — The pollen- 

 grains in cotton are almost spherical in shape. They are 

 composed of two coats or walls which inclose a thickened, 

 granular fluid.^ According to Balls ^ the pollen-grains 

 are formed in groups of four. At first, each grain posses- 

 ses only one nucleus. Later the nucleus divides, forming 

 the two male gametes. At this stage the pollen-grain is 

 mature. 



Balls states that the spores which become the egg-cells 

 (megaspores) are also formed in groups of four, "but the 

 three nearest the base of the ovule abort and only the 

 fourth member becomes a megaspore." As this megaspore 

 develops, there are given off two polar nuclei, the function 

 of which will be explained in the next paragraph. 



31. Fertilization. — The method by which the pollen- 

 grain reaches and fertilizes the egg-cell in cotton is out- 

 lined by Balls as follows: 



"The sugar solution excreted by hairs on the style 

 retains the pollen-grain and causes it to germinate. The 

 single pollen-tube traverses the tissue of the style and the 

 conducting tissues till the end enters one of the loculi, 

 along the wall of which it passes till it finds the micropyle 

 of an ovule. Traces of branching may be seen at this 

 point. Passing through the micropyle channel to the 



• Bureau of Plant Ind. U. S. Dept. Agr. Bui. 222, p. 20. 

 " Watts, " The Wild and Cultivated Cotton Plants of the World," 

 p. 344. 



' Balls, W. L., " The Cotton Plant in Egypt," p. 10. 



