Page:The Book of the Aquarium and Water Cabinet.djvu/36

26 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 number 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. M. 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