BOTANY OF THE CEYLON PATANAS. 325 
savannahs, the periodic fires, which destroy the aerial parts of 
all the less-resistant species, are a controlling factor in the 
seleetion of perennials possessing subterranean parts which 
resist the action of fire and from which the aerial parts are 
reproduced in the following season. 
The “rootstock " has various forms—e. g., a rhizome, which is 
frequently very deep in the ground (Pteris); a small herbaceous 
structure (Lagenophora, ete.) ; an erect and fleshy body (Curculigo, 
in which it is sometimes as much as 12 inches long); a tuber 
(Drosera peltata) ; or a gnarled woody, more or less branched 
body (Knoxia, and the majority of the shrubby species). The 
root-system is, as a rule, highly developed, 1. e., much branched 
and widely spreading. Tuberous fleshy roots are common 
(Curculigo, Lagenophora, Heracleum, etc.). Six species of ground 
orchids, with root-tubers, are also present, and associated with 
them is a Mycorhiza, at least in some cases. The grasses are 
tufted in habit, except at high elevations, and low in growth ; 
their leaves are narrow, rough, stiff, and usually erect. Lichens, 
mosses, and algw are quite absent from the dry patanas, and 
rare even at higher elevations ; both Sphagnum and Polytrichum 
are found in swampy places; Usnea grows luxuriantly upon the 
Rhododendron above 6000 feet; and a Collema is sometimes 
present on the damp surface of the ground among the grasses. 
Where the grasses grow in thick tufts with damp shady ground 
between them, there flourishes a flora of low, delicate shade- 
plants; these include species of Viola, Potentilla, Serpicula, 
Hydrocotyle, etc. 
The evaporating and illuminating effects of the sun’s rays 
are very effective all over the patanas, particularly below 
4500 feet; over which, as we have seen, the sun is much less 
obscured by cloud than at higher elevations. In relation with 
this we find that characters which tend to effect the regulation 
of transpiration, and a lessening of the degree of illumination 
of the leaves and other easily injured parts, are commonly 
developed. Among the more obvious of these are :— 
The rolling of the leaf; which is, however, never very 
pronounced, for, as on the savannahs, the **erieoid" and “ pinoid” 
types of rolled leaves are entirely wanting (39). 
Plants with very small, usually linear leaves are common. 
Leaves are frequently numerous and crowded together—a con- 
dition in which the majority are shaded at the expeuse of the rest. 
