The bottom being planted, the water may be introduced through a watering-pot, or poured against the side of the tank, so as to avoid any violent agitation of the bottom.  The water should be pure and bright.  River-water is best; spring-water will do, but must be softened by the plants for some days before the fishes are put in.

Sunshine is good for the tank at all seasons of the year.  The fresh- requires more than the salt-water aquarium.  The amount of oxygen given off by the plants, and hence their growth and the sprightliness of the fishes, are very much increased while the sun is shining on them.

In selecting plants for the aquarium some regard is to be paid to the amount of oxygen they will evolve, and to their hardiness, as well as to their beauty.  When it is desired to introduce the fishes without waiting long for the plants to get settled and to have given off a good supply of oxygen, there is no plant more useful than the Callitricke, or Brook Star-wort.  It is necessary to get a good supply, and pick off the green heads, with four or six inches only of stem; wash them clean, and throw them into the tank, without planting.  They spread over the surface, forming a rich green ceiling, grow freely, and last for months.  They are continually throwing out new roots and shoots, and create abundance of oxygen.  Whenever desired, they can be got rid of by simply lifting them out.

The Vallisneria, or Tape-Grass, common in all our ponds, is essential to every fresh-water tank.  It must be grown as a bottom-plant, and flourishes only when rooted.  The Nitella is another pleasing variety.  The Ranunculus aquatilis, or Water-Crowfoot, is to be found in almost every pond in bloom by the middle of May, and continues so into the autumn.  It is of the buttercup family, and may be known as a white buttercup with a yellow centre.  The floating leaves are fleshy; the lower ones finely cut.  It must be very carefully washed, and planted from a good joint, allowing length enough of stem to reach the surface.  Some of the blossom-heads may also be sprinkled over the surface, where they will live and bloom all through the summer.  The Hydrocharis, or Frog’s-Bit, and the Alisma, or Water-Plantain, are also easily obtained, hardy and useful, as well as pleasing.  Many rarer and more showy varieties may be cultivated; we have given only the most common and essential.  All the varieties of Chara are interesting to the microscopist, as showing the phenomenon of the circulation of the sap, or Cyclosis.

Of the living tenants of the aquarium, those most interesting, as well as of the highest organization, are the fishes.  And among fishes, the family of the Cyprinidae are the best adapted to our purpose; for we must select those which are both hardy and tamable. Cyprinus gibelio, the Prussian Carp, is one of the best.  It will survive, even if the water should accidentally become almost exhausted