iv ON PLANT LIFE 161 



second time when they are ready to be carried 

 away by the wind. 



Valisneria spiralis is a very interesting case. 

 It is a native of European rivers, and the 

 female flower has a long spiral stalk which 

 enables it to float on the surface of the water. 

 The male flowers have no stalks, and grow 

 low down on the plant. They soon, however, 

 detach themselves altogether, rise to the sur- 

 face, and thus are enabled to fertilise the 

 female flowers among which they float. The 

 spiral stalk of the female flower then contracts 

 and draws it down to the bottom of the water 

 so that the seeds may ripen in safety. Many 

 plants throw or bury their seeds. 



The sensitive plants close their leaves when 

 touched, and the leaflets of Desmodium gyrans 

 are continually revolving. I have already 

 mentioned that the spores of seaweeds swim 

 freely in the water by means of cilia. Some 

 microscopic plants do so throughout a great 

 part of their lives. 



A still lower group, the Myxomycetes, 

 which resemble small, more or less branched, 

 masses of jelly, and live in damp soil, among 



