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A TEXTBOOK OF THEORETICAL BOTANY 



rising to the surface of the water, pollen grains are freely distributed 

 through all layers of water. This mixing of the pollen through the water is 

 further assisted by bending movements of the plant's stem. 



Fig. 1224. — CeratophyUiun demersiim. A, Plant with male and female flowers. B, Male 

 flower. C, The same in section. D, Single stamen. E, Female flower. F, The same in 

 section. G, Diagram of the female flower. /= bract. H, Transv'erse section of fruit. 

 J, Median vertical section of fruit with embryo. K, Germinating fruit. [In H, J and K, 

 c = cotyledon ;/= first leaf pair.] {After EngJer.) 



The female flowers are produced in much smaller numbers than the 

 males. Each consists of a many-parted perianth surrounding the ovary, 

 which is unilocular and contains a single orthotropous ovule. The style 

 projects about four times the length of the perianth and is bent like a hook 

 which tapers to a point. The whole lower surface secretes a sticky sub- 

 stance and serves as a stigma. The movements of the stem not only help 

 to distribute the pollen, but may also help, by moving the attached female 

 flowers, to increase the chance of the stigmas coming into contact with the 

 pollen grains which are dispersed in the water. 



{h) Pollination at the water surface (Epihydrogamic) 



This type of pollination is more common than the last and is found in a 



