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A TEXTBOOK OF THEORETICAL BOTANY 



so that the developing ovaries mature below the water and it is there that 

 the fruit is produced. 



The case of ValUsneria spiralis (Fig. 1226) differs from that of Riippia 

 in that the whole male flower, not only the pollen, is detached and floats to 

 the surface of the water. The movement thereon of the male flower is due 



Fig. 1226. — I'dllisnerid spiralis. Female flower with curled stigmas, held 

 in the centre of a surface depression of the water, and free-floating male 

 flowers trapped in the depression. (After ]]\vlie.) 



more to the action of the wind than to the water. The female flowers are not 

 detached but are raised to the surface on long spiral stalks. There they open, 

 but as they are waxy they are not wetted and cause a slight depression in 

 the surface film of the water. The male flowers are produced in large num- 

 bers. They are released below water and open on the surface. Their three 

 sepals open widely and are slightly reflexed so that they rest on the surface 

 film and the two anthers are held vertically. The pollen from both anthers 

 clings together into one sticky mass. As the males float about, numbers of 

 them slide into the depressions around the female flowers, where they tend 

 to tip over, bringing the pollen into contact with the stigmas. If a wave 

 submerges the female flower, it and the surrounding males are closely con- 

 fined in a little bubble of air, thus assisting in pollination. 



In Elodea the female flowers produce similar depressions in the water 

 surface but the male flowers explode when they reach the air and it is the 

 free-floating pollen which is caught in the depressions. 



