88 REPRODUCTION OF PLANTS. 



The provisions for ensuring this necessary 

 contact between the pollen and the stigma, are 

 among some of the most curious in nature. 

 The stamens of many plants, by a spontane- 

 ous movement, approach the pistil at the sea- 

 son when fructification should commence. The 

 action of water on the pollen, which would be 

 injurious to it, is in some cases avoided by the 

 corolla closing on the approach of rain, and in 

 aquatic plants the organs of fructification are de- 

 fended from wet, by being produced in a cavity 

 filled with air, or by the flowers being raised 

 above the surface of the water. The Vallisneria, 

 whose flowers are diaeceous (that is, the pistil 

 is situated on one plant, and the stamens on 

 another) is a very remarkable instance of the 

 method by which the contact of the two organs is 

 effected. It grows in the waters of the south 

 of Europe, strongly embedded in the mud by 

 its roots. The pistils are situated in flowers 

 which are on long peduncles, spirally rolled up 

 at first, but which uncurl till they reach the 

 surface. The flowers which bear the stamens 

 have, on the contrary, a very short peduncle, 

 but the buds form little bladders, on which 

 they float, detached from their stems, around the 



