72 POLLINATION 



side of the thallus. Each staminate flower consists of a single 

 stamen and nothing else while the pistillate flower consists of a single 

 pistil and the three are enclosed in a spathe in such a way as to appear 

 like a single flower with two stamens and one pistil. The pistillate 

 flower matures first and is ready to receive pollen several days before 

 either of the staminate flowers is ready to expose its pollen. One of 

 the stamens then elongates and the anther opens, the pollen remaining 

 heaped in the open pollen sacs. Several days later the second stamen 

 matures and exposes its pollen. Usually there are hundreds of individ- 

 uals of these plants crowded together and they are constantly being 

 jostled against one another by movements of the water due to wind or 

 other causes. The open anthers are thus almost certain to be brought 

 into contact with receptive stigmas. The dichogamy exhibited by this 

 plant makes cross pollination almost certain but the stigma is still 

 receptive when the first stamen matures so that if it has not already 

 been pollinated self-pollination may take place at that time. 



REFERENCES 



Coulter, J. M., Barnes, C. R., and Cowles, H. C: A Text-book of Botany, 

 Vol. II. Ecology, Chapter V. Reproduction and Dispersal, American Book 

 Company, 1911. 



RoDRiGO, P. A.: Pollination and the Flowers of Rice, Philippine Agric, 14, 

 155-171, 1925. 



Skene, Macgregor: The Biology of Flowering Plants, Chapter V. Reproduc- 

 tion and Dispersal, New York, The Macmillan Company, 1924. 



WoDEHOUSE, R. P.: Pollen Grains, New York, McGraw-Hill Book Company, 

 1935. 



Wylie, R. B.: The Pollination of Vallisneria Spiralis, Bot. Gaz., 63, 135-145, 

 1917. 



