1915-16.] BOTANICAL SOCIETY OF EDINHUKGH 



Rhododendron trichocladum, Franch., and its Allies. 

 By Professor Bayley Balfour, F.R.S. 



(Read 13tli April 1916.) 



This is a small group of Western Chinese species char- 

 acterised by deciduous leaves and small yelloNv precocious 

 flowers. We know more or less of four species in the 

 group — Rh. trichocladum, Franch., from the Tali Range ; 

 Rh. mekongense, Franch., from Mt. Sila on the Mekono-- 

 Salween divide ; Rh. melinantlnim, Balf. f. et Ward, from 

 East Burma close to the Yunnan boundary, near Atuntsu : 

 and Rh. xanthinum, Balf. f. et W. W. Sm., from the Shweli- 

 Salween divide. Of these Rh. trichocladum, Franch., has 

 flowered in cultivation from seeds collected by Forrest. 

 From herbarium specimens I judge that Rh. xanthinum, 

 Balf. f. et W. W. Sm., is the most desirable of the species 

 from the horticultural standpoint. 



In all the species the young parts are coated with an 

 indumentum of long, somewhat tawn}^ hairs intermixed 

 with the peltate scales of a lepidote surface. As elsewhere 

 amongst Rhododendrons, the stalks of the scales are sunk 

 in shallow pits of the laminar surface, but the disk of the 

 scale is well outside the pit, and this allows its maroinal 

 series of cells to expand as a peripheral fringe. Here the 

 component cells of the fringe remain in contact one with 

 the other throughout their extent and do not branch, so 

 that the fringe is entire. The hairs, which may be stifl" and 

 erect {Rh. trichocladum, Franch.) or lanate and interwoven 

 {Rh. xanthinum, Balf. f. et W. W. Sm.), may persist on the 

 twigs to the second year or longer, or may fall off" early, 

 and similarly the leaf may, except on the petiole and the 

 base of the midrib above and below, lose entirely the hairs 

 but all stages of the shedding are to be met with. The 

 under surface of the leaf in all the species is less markedly 

 coated with wax than is the case in the small yellow- 

 flowered species of the Brachyanthum group; indeed in 

 Rh. trichocladum, Franch., one can liardly speak of the 

 surface as having a " bloom." Correlated Avith this, the epi- 

 dermal papillae, which carry the wax, are short and conical. 



The general similarity in flower structure that marks tl;e 



