Fig. 57.—Back view of a Flower of Rhododendron Maximum, and Seed-pod.
Fig. 58.—Flower of Rhododendron Ponticum.
The species of the genus Rhododendron are easily distinguished by their flower buds, which are disposed in the form of a strobile, or pine-cone, each bud having its accompanying bract, which the flower retains after its expansion, as shown in fig. 57 at a, in a flower of R. maximum. There are five or ten stamens of unequal length, the larger ones curling upwards (as shown at b in fig. 58), as does the style (c), which has a simple stigma. The flowers have a very small calyx, (d in fig. 57,) and a campanulate corolla which is deeply five-cleft, the upper segment (e in fig. 58) being somewhat larger than the rest, and spotted in the inside. The capsule is five-celled and five-valved, as shown in fig. 57 f. The leaves of nearly all the species are evergreen; and the flowers are showy, and produced in terminal corymbs. The principal species may be thus distinguished from each other; R. maximum has drooping leaves, covered with brown or white down on the under surface, and a dense corymb of flowers, the segments of the corollas of which are roundish, and the bracts leafy. In R. ponticum, on the contrary, the corymbs of flowers are looser, the segments
Fig. 59.—Seed-pod of Rhododendron Ponticum. more pointed, and the bracts more scale-like; and the leaves are smooth on both surfaces. The seed-pods also differ: in those of R. maximum and the other American species, the valves are smooth as shown at f in fig. 57; and in those of R. ponticum, the valves are somewhat crinkled as shown in fig. 59. This species, and all its hybrids and varieties, are more tender than R. maximum, R. catawbiense, and all the other American kinds and their offspring. R. catawbiense has the flower of a darker colour on the outside of the corolla than within, and the upper segment is very faintly dotted. It hybridises freely with R. arboreum, which R. maximum does not, and the hybrids thus produced are hardier than those raised from R. ponticum, though the latter are by far the most numerous.
Most of the species have purple or whitish flowers, but some, such as R. chrysanthemum, and R. anthopogon, have yellow flowers; R. ferrugineum and R. hirsutum, have bright pink or rose-coloured flowers; and those of R. arboreum the Nepaul tree Rhododendron, are of a rich scarlet. The commonest small kinds are R. ferrugineum and R. hirsutum, both dwarf shrubs and natives of the north of Europe, with funnel-shaped corollas, and leaves dotted on the under surface. They are so much alike as scarcely to be distinguished at first sight, but on examination the leaves of R. ferrugineum will be found to have brown dots, and to be plain on the margin; while those of R. hirsutum have white dots and are fringed with fine hairs.
Of all the species of the genus, those which differ most widely from the others are the Indian kinds. Of these R. arboreum has a ten-celled capsule, and the segments of the corolla two-lobed with waved margins. The leaves are long and silvery beneath; and the capsules, the peduncles, and the calyxes, are all woolly. In R. campanulatum, a splendid species with very large flowers, the capsule is six-celled, the leaves are somewhat cordate at the base, and the bracts are fringed; and in R. anthopogon the corolla has a cylindrical tube, woolly inside, and a small but spreading limb, cut into five lobes. There are eight stamens, and the capsule is five-celled.
R. Camtschaticum, R. Chamæcistus, and R. dauricum differ from the preceding species in having their corollas rotate, that is, wheel-shaped. The last of these kinds is a favourite greenhouse shrub, from its flowering under shelter in winter. In the open ground it flowers in March. The species has rose-coloured flowers which appear before the leaves; and leaves which turn red in autumn before they fall. The roots are knobbed and fibrous; and the stems are twisted and knobbed in a wild state. There is a variety R. d. atrovirens which has purple flowers, and evergreen leaves, and which is hardier than the species.