160 TRANSACTIONS OF THE [Sess. lxxxi 



evergreen species of Rhododendron. The revolution of the 

 lamina makes the upper surface the exposed one, excepting 

 the midrib (here raised) of the under surface against which 

 the curled sides of the lamina abut. The upper surface 

 and the exposed midrib area of the under side are in the 

 four species (Rh. agastwm, Bh. araiophyllum, Kit. hylo- 

 threptiiin,Rh. irroratu77i),oi which alone we know the young 

 leaves, densely clad with indumentum. Its elements may 

 be hairs with a stout foot and branching freely above, 

 often very long and interwoven, white at first and becom- 

 ing more or less orange or red, and taking on the greasy 

 appearance so often seen in Rhododendrons {Rh. agastwm, 

 Rh. araiophyllum). The whole surface may thus be 

 what is known by the generic term tomentose, and this 

 tomentum, composed of flocks of greasy hairs, is a floccose 

 greasy tomentum. Or there may be an admixture of 

 clavate-.stalked red glands with similar stout bases (Rh. 

 hylothreptum) and the glands may predominate (Rh. irro- 

 ratuin). The same covering may spread over the petiole. 

 The under leaf-surface, concealed by the rolling back- 

 wards of the sides of the leaf, bears also floccose hairs with 

 stout bases, but they are fewer, not in contact, and the 

 branches are shorter, more prostrate and radiating ; there 

 may also be clavate glands and cauliflower glands. (In 

 Rh. araiophyllum tlie under surface appears to be glabrous 

 except on the primary veins and midrib.) Along the 

 margin glands and flocks are also developed. As the 

 leaves unfold the glands and the flocks fall ofl" always 

 above the foot or base, which remains as a red or orange- 

 coloured cone blackening with age, and is the cause of 

 the punctulation of the leaf-surface in the mature leaf. 

 Punctulations on tlic petiole and on the stems are 

 developed in like manner. In no species, with the 

 exceptions hereafter mentioned, have I seen the juvenile 

 indumentum persisting throughout on the mature leaves 

 and petioles and stems. But if my description has made 

 clear the happenings during the passage from youth to 

 maturity, the persistence of some part of the indumentum 

 in a more or less perfect state is an occurrence that will 

 not cause surprise. In some species this persistence is 

 more marked than in others. Rh. agastum retains as a thin 



