580 



HYDROCHARIDACE^. 



HYDR<5CHARIS MOESUS-RAN^S 



flower to float on the surface for a few hours, and then 

 contracts again, drawing the seed-vessel beneath the 

 surface, there to ripen its seeds. The number of species 

 is small, and two only are natives of Britain. Within 

 the last few years, however, a species new to Britain 

 has made its appearance, and has increased to such an 

 alarming extent, as to impede the navigation of some of 

 our canals. This is Anacharis Alsinastrum, a submerged 

 aquatic, having much of the habit of Potamogeton 



