JUGLANS REGIA, Common Walnut
- Juglans regia, Linnæus, Sp. Pl. 997 (1753); Loudon, Arb. et Frut. Brit. iii. 1421 (1838).
A deciduous tree, attaining 100 feet in height and 15 to 18 feet in girth. Bark smooth and silvery grey in young trees, becoming ultimately more or less deeply fissured.
Leaves large, up to 10 inches long, coriaceous, of five to nine (rarely as many as thirteen) leaflets, sub-opposite or opposite, the terminal leaflet stalked, the others subsessile ; elliptic, long-ovate or obovate, shortly acuminate at the apex, tapering and unequal at the base, glabrous on both surfaces, except for inconspicuous tufts of pubescence in the axils of the nerves on the lower surface; dark green above, paler beneath, entire or slightly sinuate in margin; exhaling an aromatic odour. Venation pinnate, with ten to fourteen pairs of lateral nerves, which run nearly straight to near the margin, where they curve forwards and join with the next vein. The leaflets diminish in size from the apex to the base of the leaf. Rachis glabrous, terminal leaflet not articulated. Young shoots glabrous, with yellow sessile glands and white inconspicuous lenticels.
Male catkins arising singly or in pairs (one above the other) above the leaf-scars of the previous year’s shoots, green, two to five inches long, sessile, pendulous, thickly cylindrical and densely flowered; flowers with stalked bracts, two to five perianth leaves and two bracteoles; stamens ten to twenty; anthers oblong, apiculate. Female flowers, one to four, at the apex of the young shoots, green, with usually purple stigmas ; involucre minute, indistinctly four-toothed ; perianth green, with four linear-lanceolate divisions.
Fruit globular, about two inches in diameter ; pericarp green, smooth, glandular- dotted, coriaceous, and very aromatic, splitting irregularly when mature. Nut very variable in shape, wrinkled and irregularly furrowed, thin- or thick-shelled; divided interiorly by two thin dissepiments into four incomplete cells ; one dissepiment separat- ing the two cotyledons, the other dissepiment dividing them into two lobes. The structure of the fruit of the walnut is very complicated, and the reader is referred for further details to Lubbock’s paper’ on the fruit and seed of the Juglandeæ.
The common walnut, according to Kerner,” is truly monœcious, the stigmas, however, ripening several days before the pollen is shed from the anthers.’ The unripe male catkins have the flowers crowded together in a short thick spike directed upwards. As soon as the pollen develops the spike elongates to three or four times its former length and becomes loose and pendulous, the flowers
1 Jour. Linn. Soc. (Bot.), xxviii. 247 (1890). Cf. also Lubbock, Seedlings, ii. 506 seq. (1902). Malformed walnuts are occasionally produced, which are very curious. Cf. Gard. Chron. 1858, p. 5, and 1890, viii. 758, fig. 154.
2 Cf. Kerner, Nat. Hist. Plants, Eng. trans. i. 742, fig. 184 (1898).
3 This is not invariable. Delpino observed that while certain trees of the common walnut were protogynous, i.e, the stigmas ripening first, other trees were protandrous, the stigmas ripening after the anthers. In such cases the trees behave as if they were diœcious. Cf. Darwin, Diff. Forms of Flowers, 10 (1877), and Trelease, Missouri Bot. Garden Report, vii. 27 (1896).
