304 BALFOUR—NEW SPECIES OF RHODODENDRON. 
species of Croton, and others. This is well represented in Rh. 
cuneatum, Rh. hippophaeoides, Rh. idoneum, Rh. intricatum, 
Rh. polifolium, Rh. tapetiforme, Rh. Websterianum. One speaks 
of the scales as uniform or concolorous. The surface may be 
'grey-coloured, or if the scales are tinted brown it becomes a 
bright brown or a rusty brown. But in some cases, eg., Rh. 
achroanthum, Rh. capitatum, Rh. chryseum, Rh. rupicolum, about 
half of the scales equally distributed over the leaf-surface become 
tinted brownish and are intermixed with the other half, which 
remain whitish or grey-green. There appear to be two kinds of 
scale. But the scales are all of the same build; it is in the 
coloration that there is difference, and also in the stalks, which in 
the brown scales are a little longer and the scale-disks are there- 
fore projected somewhat beyond their untinted fellows. And 
then we pass to species in which only a few of the scales de- 
velop longer stalks and become brown, as in Rh. diacritum, 
Rh. drumonium, Rh. nigropunctatum, Rh. nivale, Rh. pycno- 
cladum, Rh. telmateium, Rh. thymifolium, and others, so that the 
greyish or brownish leaf-surface is picked out with dark brown 
spots—it is punctulate. We speak of the scales in the two cases last 
described as biform or bicoloured. What functional meaning, 
if any, there is in the modification is not evident, unless it 
be that the projection of many or few of the contiguous scales 
secures more free communication between the stomata and the 
atmosphere—a suggestion the validity of which is questioned 
by the occurrence of like disposition on leaf-surfaces where the 
scales are discontiguous. Leaf under-surfaces with discon- 
tiguous scales may appear grey or tinted brown or brown mixed 
with green. The grey and green of the surface depends upon 
the area of surface exposed between the scales and the develop- 
ment of wax on the epidermal papillae; the brown tint is a 
consequence of the coloration of the scales. 
Examination of dried specimens and of the few species that 
are in cultivation tells me that this indumentum character of 
the old leaves is a good basal one of definition. 
The twigs of all the Lapponicum Rhododendrons are alike. 
They may be longer or shorter, but are all coated with a rusty 
indumentum of peltate scales which peal off like scurf. 
In no one of the Lapponicum series have I found on the 
stems and petioles the very long-stalked peltate scales which 
lose sooner or later their disk—the stiffened stalk becoming there- 
after a longer or shorter seta. These setulose scale-stalks are well 
developed in the Anthopogon, Fragrans, and Cephalanthum 
series. See what I say on p. 318. In this Lapponicum series the 
scale-remnant sometimes forms a little wart on the branch- 
lets before the grey bark begins to shred off, but that is all. 
