Two of the three species which form the subject of this article are not only highly ornamental, but also valuable timber trees. Until recently they were considered to belong to the genus Planera, which, however, consists of but a single New World species; now, they properly constitute a distinct genus, viz., Zelkova, which differs materially from the true Planer tree in the structure of the fruit, etc. Z. crenata, from the Caucasus, and Z. acuminata, from Japan, are quick growing, handsome trees, with smooth bark not unlike that of beech or hornbeam; it is only when the trees are old that the bark is cast off in rather large sized plates, as is the case with the planes. The habit of both is somewhat peculiar; in Z. crenata especially there is a decided tendency for all the main branches to be given off from one point; these, too, do not spread, as for instance do those of the elm or beech, but each forms an acute angle with the center of the tree. The trunks are more columnar than those of almost all other hardy trees. Their distinct and graceful habit renders them wonderfully well adapted for planting for effect, either singly or in groups. The flowers, like those of the elm, are produced before the leaves are developed; in color they are greenish brown, and smell like those of the elder. It does not appear that fruits have yet been ripened in England. All the Zelkowas are easily propagated by layers or by grafting on the common elm. [Illustration: YOUNG ZELKOWA TREE (21 FEET HIGH)] _Zelkcova crenata_--The Caucasian Zelkowa is a native of the country lying between the Black and the Caspian Sea between latitudes 35° and 47° of the north of Persia and Georgia. According to Loudon, it was introduced to this country in 1760, and it appears to have been planted both at Kew and Syon at about that date. A very full account of the history, etc., of the Zelkowa, from which Loudon largely quotes, was presented to the French Academy of Science by Michaux the younger, who speaks highly of the value of the tree. In this he is fully corroborated by Mirbel and Desfontaine, on whom devolved the duty of reporting on this memoir. They say that it attains a size equal to that of the largest trees of French forests, and recommend its being largely planted. They particularly mention its suitability for roadside avenues, and affirm that its leaves are never devoured by caterpillars, and that the stems are not subject, to the canker which frequently ruins the elm. The name Orme de Siberie, which is or was commonly applied to Zelkova crenata in French books and gardens, is doubly wrong, for the tree is neither an elm nor is it native of Siberia. In 1782 Michaux, the father of the author of the paper above mentioned, undertook, under the auspices, of a Monsieur (afterward Louis XVIII.), a journey into Persia, in order to make botanical researches. [Illustration: FOLIAGE OF A YOUNG ZELKOWA TREE, WITH FLOWERS AND FRUIT.]