26 THE FRESH-WATER AQUARIUM. 
weed as to be recognised with difficulty. Its old botanical 
name is Callitriche aquatalis, but owing to its liability to 
vary its appearance, botanists have lately divided it into 
several species, the two most common of which are C. 
autumnalis, and C. Vernalis. 
Vallisneria spiralis is essential to every fresh-water 
tank. It is a native of Italy, and is named in honour of 
the Italian naturalist, Vallisneria. The blooming of this 
plant is very curious and worthy of close scrutiny. It 
likes abundance of light, and must be grown as a bottom 
plant, flourishing only when well rooted. 
Anacharis alsinastrum, or the New Water-weed, is an 
interesting plant that grows freely, whether rooted or not; 
but it can only be considered ornamental when springing 
from the bottom. It thrives just as well without a root 
as with one, but, if firmly fixed, usually sends down a num- 
ber of white rootlets from joints on the stem. I have seen 
roots of this kind sent down six inches to reach the bottom, 
while the lower part of the stem was decaying rapidly. 
Myriophyllum contributes some lovely members to the 
aquarium. All the plants of this genera are of elegant 
structure, the leaves finely divided and of a delicate 
emerald green. MM. Spicatum is perhaps the best, but 
there are other species to be had of the dealers that are 
worthy of attention. 
Potamogeton is an extensive genera of water-plants, 
numbering not less than fifteen species in the brooks and 
rivers of this country alone. P. fluitans, crispus, and 
densus, are most easily obtained, and they flourish in the 
tank, and make rich branching masses for the centre, or to 
