Selection of Plants.—There is scarcely any aquatic plant but may be grown in an aquarium, and unless some attention is given to the botanical department, only half the pleasure and instruction it is capable of affording is attained. I cannot agree with Mr. Gosse, that the vegetation of a tank has so strictly a secondary place—"preserved because they cannot be dispensed with,"—for in either a marine or fresh-water vessel the vegetation is a special source of beauty and interest, and fairly divides attention with the animals. Supposing it were impossible to keep animals in such vessels, they would still be acceptable for the formation of aquatic gardens.
Beauty of form and adaptability to confinement are the requisites for this purpose, and the more lakes and rivers are explored, the more the botanical department of the aquarium will be extended, both as to ornament and usefulness.
STRATOIDES ALOIDES.
Water Soldier.—Among the plants easily attainable, and which combine grace of outline with cleanliness of growth, and tendency to create oxygen, I can recommend, first of all, the famous water soldier—Stratoides aloides—a lovely cactus-like plant, which grows equally well with or without a root, as indeed most water-plants do. In form it closely resembles the tuft of herbage on the crown of a pine apple, and its leaves have similar serrated edges. If thrown in, it floats on the surface, and puts forth new heads in plenty, each new head springing from the base of a leaf on a long stalk. By separating these when pretty well grown, and removing the stem from the base, any number of new plants may be formed. If it be wanted to root at the bottom (as indeed is best) cut away the decayed portion of the base, and trim off every dark-coloured leaf and throw the plant in again. In a few weeks it will throw out roots, and it may then be attached to a stone by a piece of bass, and dropped in to fix itself where wanted, without in any way disturbing the tank.
VALLISNERIA SPIRALIS.
Starwort I have already spoken of, as a good purveyor of oxygen. It is a pretty plant of a delicate green hue, which appears on the surface of brooks and ditches everywhere, both in this country and all over the continent. At a little distance it has so much the appearance of duckweed 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.