132 
I may add that | am well aware that the views given above 
are in many points open to criticism. 
The Leaf. 
Among the forms with broad leaves which persist through 
the winter Rhododendron lapponicum is doubtless the one that 
is specially Arctic, and one of the oldest forms of this region; 
consequently, it may well be.the first to be dealt with. Here 
we find a thick epidermis on both surfaces; a well-developed 
covering of peltate hairs; stomata especially well-protected ; 
several layers of small palisade-cells; and a slightly branching 
spongy parenchyma arranged in lamellæ around the large inter- 
cellular spaces. With regard to the last-named feature it may 
be mentioned that it would be quite indefensible to connect 
them at all with Arctic conditions such as, for example, the 
great dampness of air in these regions. According to LaLanse, 
leaves which may be several years’ old, provided they are not 
too small, have large intercellular spaces. This feature is not 
dependent upon any particular climate, but should rather be 
connected with the thickness of the epidermis, which affords 
good protection against the danger of excessive transpiration; 
or better still, the spaces may be rendered necessary in the 
present instance, because the stiff, coriaceous leaves cannot be 
stirred so freely by the wind as are deciduous leaves. 
Trying next to find a species which is as well protected 
as Rhododendron, we come to Ledum. This is a very common 
species in the Arctic regions, but it has in addition a much 
more southerly distribution, in districts with a continental cli- 
mate, and consequently, a severe winter. It is scarcely as typi- 
cally Arctic as Rhododendron, neither is it as old-established 
in the region as the latter. Nevertheless it is justifiable to 
surmise that its structure reflects to some extent the Arctic 
climate. The stomata are perhaps not so well protected as 
those in Rhododendron, but on the other hand we have here 
