PHYSIOLOGY OF THE COTTON PLANT 27 



"When, therefore, the water-supply is sufficient, and 

 especially when sunlight, temperature and other condi- 

 tions are favorable for leaf activity, the stomata open 

 and permit the leaf to absorb carbon dioxide. On the 

 other hand, lack of water and unfavorable conditions 

 cause them to close." 



The evaporation of water is of great advantage to the 

 plant, in that it regulates certain physical properties, 

 especially the temperature of the plant. Again, it con- 

 centrates in the leaf the food materials taken up from the 

 soil. It is in the leaf that these soluble salts meet and 

 combine with the food taken from the air, to form elab- 

 orated food such as protein. 



REPRODUCTION 



The life-story of the cotton plant does not begin with 

 the germination of the seed. The new individual begins 

 when the generative nucleus of the pollen-grain unites 

 with the egg-cell nucleus of the ovule. As a result of this 

 fusion the seed containing the embryo, or miniature plant, 

 develops. 



29. The reproductive organs. The organs of re- 

 production are the pistil and the stamens. The pistil is 

 the female organ and is composed of (1) the ovary, which 

 forms the base of the pistil and contains the ovules; (2) the 

 style, constituting the more or less narrowed column of 

 the pistil, and (3) the stigmas, composing that part of the 

 pistil, which receives the pollen-grains. The stamens are 

 the male organs of the plant. Each stamen consists of 

 (1) a filament, or thread-like stalk, and (2) the anther 

 a somewhat kidney-shaped body borne on the apex of the 

 filament and bearing the pollen-grains. 



In Egyptian cotton the style is rather long, carrying 



