Ridley. — On Endemism mid the Mutation Theory . 565 
occurrences recorded by botanists, and I would especially refer Dr. Willis 
to Hiern’s paper on ‘ Forms of Floating Leaves ’ (Cafnb. Phil. Soc., xiii); and 
call his attention to the well-known variations in Polygonum amphibium. 
The whole meaning of these adaptations of local species to local con- 
ditions is not always clear. I do not clearly see why, for instance, the Alpine 
plants of the high mountains of the Malay Peninsula and Ceylon have 
a tendency to the reduction of the whole plant in size, the thickening of the 
leaves, and their having a tendency to become eventually quite round, 
orbicular in fact, and in the case of compound leaves, simple, a state of 
affairs which does not occur in any of the species of the same genus in the 
wet forests at the base of the mountains ; but there cannot be a shadow of 
doubt that it is of importance to the plant, and that the plants have been 
gradually adapted to their surroundings. Dr. Willis seems to be puzzled 
as to why different species of a genus occur in the same region. Why, he 
asks, in the ‘Annals of the Roy. Bot. Garden, Peradeniya,’ vol. iv, p; 11— why 
should Dillenia retusa with its obtuse leaves and small flowers be found 
alongside D. indica with acute leaves and large flowers ? In the eastern 
peninsula again live D. ovata , D . meliosmaefolia , as well as D. indica . 
Why should they be better suited to the eastern peninsula while D . brae - 
teata suits Mysore and D. retusa Ceylon ? ’ I have not seen D . retusa or 
D. bracteata , and we must add D. dentata , Thunb. ( Wormia triquetra , which 
is a true Dillenia), growing wild, so I can give no answer as regards them, but 
the story of the Dillenias of the Malay Peninsula I can at least partly give® 
D. indica is exclusively confined to wet ground, chiefly river banks. 
It would not grow in the ordinary soil of the gardens of Singapore, but 
planted on the edge of ponds and in swampy grounds it did well. Its fruits 
are very large and round with immensely thickened and enlarged sepals, and 
measure 4-6 in. through. These sepals are not sweet to taste, nor is the 
fruit eaten by any animal. It is adapted for dispersal by river. River 
and sea-dispersed fruits have a tendency to become very large, e. g. Calo - 
phyllum macrocarpum , Barringtonia speciosa , Cerbera Odollam , &c., and this 
entails in many cases a corresponding enlargement of the flower, well seen 
in Di indica. D. ovata , Wall., and D. aurea, Sm., inhabit dry, xerophytic 
spots in rocky or sandy localities. They have bright yellow flowers and 
smaller-sized fruits ; both are rare in the peninsula, as the climate, except in 
the north, is unsuitable. They appear to have originated in a dry region 
and have pushed a short way into the peninsula from Siam. D. meliosmae- 
folia, Hook, fil., is a small jungle tree occurring in our wet forests. To adapt 
it for that life the leaves and shoots are densely hairy, to throw off the rain 
which otherwise would injure the leaves. Hairy leaves such as these I find 
dry after rain quicker than smooth ones, besides retaining less water on the 
leaf during a shower. The leaves and buds of the trees in the forests are 
all guarded in various ways from the action of rain, or father from the action 
Q q 
