Aquatic plants, two of which are of very curious construction. In Vallisneria, the male and female flowers are on different plants, and the buds of the female flowers rise on long spiral stalks, which gradually uncoil, till the flower appears above the surface of the water, where it expands. The male flowers are produced on separate plants at the bottom, but, before they expand, they detach themselves from the soil, and rise up to the surface, where they float till the flowers have opened, and the pollen has fallen on the stigmas of the female flowers, after which the male flowers wither, and the female ones coil up their stalks again to ripen the seed-vessels at the bottom. This curious arrangement is necessary, because the pollen should be dry when it falls on the stigmas; and nearly a similar arrangement takes place with the Fresh-water Soldier (_Stratiotes_). The Frog’s Bit (_Hydrocharis morsus ranæ_) is a floating plant, with pretty white flowers. _Damosonium indicum_ is a very handsome water-plant, with white flowers and winged stems. ORDER CLXXX.—ALISMACEÆ.—THE WATER PLANTAIN TRIBE. The principal genera in this order are Alisma, Sagittaria, and Actinocarpus, all common British aquatic plants. The Water Plantain (_Alisma plantago_) has ribbed leaves, and a loose panicle of small pinkish flowers, which have a permanent calyx of three sepals, a corolla of three petals, six stamens, and numerous carpels, which grow close together so as to form a head, as in the Ranunculus tribe. _A. natans_, which is generally found on lakes in the mountainous districts of Wales and Cumberland, has rather large white flowers, with a yellow spot at the base of each petal. The flower-stalks rise high above the water, and the flowers expand in the months of July and August. The common Arrowhead (_Sagittaria sagittifolia_) has curiously-shaped leaves, resembling the head of an arrow. The flowers are white, and resemble those of _A. natans_; but they have a pink spot at the base, and there are numerous stamens. The flowers are in whorls, and those in the upper whorls are generally destitute of carpels. The common Star-fruit (_Actinocarpus damsonium_) has only six carpels, which are so arranged as to form a star-like fruit when ripe. ORDER CLXXXI.—BUTOMEÆ.—THE FLOWERING RUSH TRIBE. The flowering Rush (_Butomus umbellatus_) is certainly the handsomest of the British aquatic plants. The flowers are rose-coloured, crimson, or white; and they are produced in large erect umbels. The calyx and the corolla are generally of the same colour, and in three divisions each; there are nine stamens and six capsules, which are many-seeded. The leaves are triangular or flat. _Limnocharis Plumieri_ is a very handsome Brazilian aquatic belonging to this order. ORDER CLXXXII.—JUNCAGINEÆ.—THE ARROWGRASS TRIBE. Insignificant bog plants, with grassy leaves, and central spikes or racemes of greenish yellow flowers. ORDER CLXXXIII.—ORCHIDACEÆ.