76 BALFOUR—NEW SPECIES OF RHODODENDRON. 
made in the case of Rh. dimitrum and of Rh. neriiflorum 
(see p. 54). 
The flower-character of difference between Rh. sanguineum 
and Rh. haematodes 5 petals, 10 stamens in the former, 6 petals 
12 stamens in the latter, is not a valid one. Both species are 
characteristically pentamerous. 
Where Franchet does furnish definite point for diagnosis is 
in the indumentum of the leaf underside. Here there is an 
easily recognisable difference, although fundamentally the in- 
dumentum in the two species is moulded on the same lines. I 
refer to this specially, because Franchet shows customary per- 
spicacity in his appreciation of indumentum. The indumentum 
_ of Rh. sanguineum on the leaf underside forms a thin white 
covering smooth and scintillating. Under magnification the 
surface appears honeycombed by the interlacing of hairs spread- 
ing out more or less parallel with the plane of the leaf-surface ; 
the whole surface is compact, there are no long hairs standing 
up like wool. The indumentum is formed of a series of shortly- 
stalked hairs, the stalks relatively stout and from the top giving 
off many horizontally spreading branches, the branches of 
adjacent hairs overlapping and interpenetrating, each branch 
being a thin-walled broad cell vesicular when mature. The 
branch-system forms a canopy over the leaf-surface supported 
as it were on pillars formed by the hair-stalks, and thus a chamber 
of still air, so important a contrivance for checking rapidity of 
transpiration, is provided. But these stalks are not all of quite 
the same length, and some of the hairs have stalks so short 
as to give them a different appearance from their neighbours 
with longer stalks. There is therefore an approach to a bistrate 
character in the indumentum, though it is not of the conspicuous 
well-marked character found in some other species of Rhodo- 
dendron. But it is significant that in species very closely 
allied to Rh. sanguineum, for instance in Rh. citriniflorum, 
Balf. f. et Forrest (see p. 37), an emphatic development of the 
bistrate type occurs, and this may be regarded as a link between 
the less-developed state in Rh. sanguineum and the much more 
developed state in Rh. haematodes. For in Rh. haematodes a 
bistrate indumentum is typical. Its surface is buff-coloured, 
not white. No magnification is necessary to show its loose 
honeycombed surface, and if one does use a lens of even 
low magnifying power the long openly interwoven threads 
of the hair-branches stand out upon the surface in very 
different fashion from what is seen in Rh. sanguineum, and 
pressure with the finger of the surface in the two cases reveals 
to touch the soft resilient thick woolliness in Rh. haematodes 
in contrast with the hard unimpressible surface in Rh. san- 
