
THE FRESH-WATER AQUARIUM. 209 
of them being averse to the light if it is strong; second, as 
à means of concealing the sediment which, without doing 
any material injury, so mars the beauty of an aquarium; 
third, as a means for anchoring in their proper place the 
plants we put in; fourth, and lastly, to make the effect of 
the aquarium more like nature. 
It is generally thought that most water-plants, to do well 
in an aquarium, must have soil to grow in as well as land- 
plants, and that a layer of earth or sand must be spread over 
the bottom of the tank for the roots; this is found by ex- 
perience to be a mistake. No earth nor sand is required 
for the plants which grow best in the aquarium. Either is 
Very apt to spoil the water after remaining in contact with 
it a short time. Coarse sand is, to be sure, sometimes used 
When we have animals in the tank whose nature it is to bur- 
TOW, but even then only in a small quantity placed near a 
corner of the tank. Some of the small lilies grow better if. 
they have a cubic inch of peat attached to their roots. This 
" small quantity does not injure the water, however long it 
may remain in it, and. is often very useful. In general, 
however, if the plants are placed right side up, among small 
stones about the size of a fresh pea, they will grow to any 
extent, seldom throwing out roots of any kind. 
e want, then, a layer of small stones on the bottom, 
about an inch in thickness; this will be sufficient to bury the 
ends of the plants in, and to conceal all the sediment which 
may collect, at the same time giving depth enough for the 
Mussels to burrow in. The stones used with tar for the tops 
of houses are about the right size for this layer, and. on the - 
top of it some larger stones about the size of an almond 
may be seattered here and there. As to the color of the 
stones this may add greatly to the effect. If we can have 
the patience to pick out for ourselves the white and varie- 
ated stones from the beaches, we shall be amply repaid by 
their appearance in water. White stones give a brighter 
look to the inside of the tank than dark-colored ones, and 
AMER. NATURALIST, VOL. III. 27 : 
