WATER PLANTS. 89 



star- wort (Callitriche verna), the horn- wort (Cerato- 

 phyllum demersum), and the pond weeds (Potamo- 

 geton), of which we have several abundant species, 



Fig. 39- 



Villarsia nymphczoides. 



easily procurable. The water milfoil (Myriophyllum 

 spicatum) is a very common and graceful aquarium 

 plant. Its greenish flower spike is often raised un- 

 obtrusively above the water ; whilst its submerged 

 thread-like leaves are arranged in whorls of four in 

 number. This is the commonest of our British 



