1911 Encyclopædia Britannica/Laburnum
LABURNUM, known botanically as Laburnum vulgare (or Cytisus Laburnum), a familiar tree of the pea family (Leguminosae); it is also known as “golden chain” and “golden rain.” It is a native of the mountains of France, Switzerland, southern Germany, northern Italy, &c., has long been cultivated as an ornamental tree throughout Europe, and was introduced into north-east America by the European colonists. Gerard records it as growing in his garden in 1597 under the names of anagyris, laburnum or beane trefoyle (Herball, p. 1239), but the date of its introduction into England appears to be unknown. In France it is called l'aubour—a corruption from laburnum according to Du Hamel—as also arbois, i.e. arc-bois “the wood having been used by the ancient Gauls for bows. It is still so employed in some parts of the Mâconnois, where the bows are found to preserve their strength and elasticity for half a century” (Loudon, Arboretum, ii. 590).
Several varieties of this tree are cultivated, differing in the size of the flowers, in the form of the foliage, &c., such as the “oak-leafed” (quercifolium), pendulum, crispum, &c.; var. aureum has golden yellow leaves. One of the most remarkable forms is Cytisus Adami (C. purpurascens), which bears three kinds of blossoms, viz. racemes of pure yellow flowers, others of a purple colour and others of an intermediate brick-red tint. The last are hybrid blossoms, and are sterile, with malformed ovules, though the pollen appears to be good. The yellow and purple “reversions” are fertile. It originated in Paris in 1828 by M. Adam, who inserted a "shield” of the bark of Cytisus purpureus into a stock of Laburnum. A vigorous shoot from this bud was subsequently propagated. Hence it would appear that the two distinct species became united by their cambium layers, and the trees propagated therefrom subsequently reverted to their respective parentages in bearing both yellow and purple flowers, but produce as well blossoms of an intermediate or hybrid character. Such a result may be called a “graft-hybrid.” For full details see Darwin's Animals and Plants under Domestication.
The laburnum has highly poisonous properties. The roots taste like liquorice, which is a member of the same family as the laburnum. It has proved fatal to cattle, though hares and rabbits eat the bark of it with avidity (Gardener's Chronicle, 1881, vol. xvi. p. 666). The seeds also are highly poisonous, possessing emetic as well as acrid narcotic principles, especially in a green state. Gerard (loc. cit.) alludes to the powerful effect produced on the system by taking the bruised leaves medicinally. Pliny states that bees will not visit the flowers (N.H. xvi. 31), but this is an error, as bees and butterflies play an important part in the fertilization of the flowers, which they visit for the nectar.
The heart wood of the laburnum is of a dark reddish-brown colour, hard and durable, and takes a good polish. Hence it is much prized by turners, and used with other coloured woods for inlaying purposes. The laburnum has been called false ebony form this character of its wood.