ORDER XXX.—BYTTNERIACEÆ.—THE BYTTNERIA TRIBE.
This order is divided into five sections, which some botanists make distinct orders. It is very nearly allied to Malvaceæ, but the anthers are two-celled. The principal genus in the first section (Sterculieæ) is Sterculia, which has several carpels distinct and arranged like a star: the species are trees with large handsome leaves which are articulated at the base, and axillary panicles or racemes of flowers. The second section (Byttnerieæ) contains among other plants Theobroma Cacao, from the fruit and seeds of which Cocoa and Chocolate are prepared. The third section (Lasiopetaleæ) is well known in England, by the pretty Australian shrubs included in the genera Thomasia and Lasiopetalum, the leaves of which have their under surface downy, and generally brown. The fourth section (Hermannieæ), and the sixth (Wallichieæ), contain no plant common in English gardens; and the fifth (Dombeyaceæ) is best known by Astrapæa Wallichii. The qualities of all the plants in this order are mucilaginous.
ORDER XXXI.—TILIACEÆ.—THE LINDEN TRIBE.
The only genus belonging to the natural order Tiliaceæ which is easily to be procured in Britain is that of Tilia, the Lime trees. The common Lime (Tilia europæa) is generally a tall, well-formed tree, with rather broad leaves, which are heart-shaped at the base, tapering at the point, and serrated at the margin: they are also smooth on the outer surface, thin, and of a light and delicate texture; below there is a little tuft of hair at the angle of the veins. The flowers are produced in cymes or compound
Fig. 120.—The flowers and seed-vessel of the common Lime tree. umbels (see fig. 120); and their main pedicel appears to spring from one long entire bract (a). The calyx is in five sepals, and it falls off before the corolla, which is composed of five pale yellow petals, which are very sweet-scented.
The stamens are numerous, and the filaments separate, bearing two-celled anthers, which burst by long slits. The ovary has only one style, the tip of which is cleft into five small stigmas; and it is divided into five cells, each containing one or two ovules. The fruit or capsule (b) is round, and has a leathery skin, covered with a soft down; and when ripe, the cells often become united so as to form one, with only one or two perfect seeds in the whole capsule, the other ovules proving abortive. The whole plant abounds in mucilage, and the sap when boiled affords sugar. The inner bark is so tough and fibrous, that it is used for making what are called bast mats: it being first rendered flexible by steeping it for a long time in water. The wood is of very fine texture, but soft and white, and it is thus admirably adapted for carving. The American Limes have a small scale at the base of each petal of the flower; but the other differences between the species are very slight.