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 HKuropean 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 
M 
