ENEMIES AND FRIENDS 187 



There are certain water plants which 

 have a tendency to take possession of an entire 

 pond and need keeping within bounds. 

 Such a plant is the water chestnut (Trapa 

 natans). Its fruits, provided with strong 

 prongs, lodge in the debris at the bottom of 

 the ponds. Often, in the spring, the entire 

 surface of a large pond will be covered with 

 young plants. Even their removal in boat- 

 loads will not suffice to get rid of the plant 

 which, of comparatively recent introduction, 

 has now become a pest in some localities. 

 Removal does no good as there are always 

 more seeds on the bottom of the pond. 



It is inadvisable to use this particular plant, 

 as a cultivated one, in any but concrete ponds, 

 which, at least, can be thoroughly cleaned 

 when the need arises. 



During the winter the tubers of the various 

 water-lilies that are stored in the greenhouse, 

 must be carefully protected from the depre- 

 dations of rats and mice that find them most 

 delectable morsels. 



