BOTANY OF THE CEYLON PATANAS, 323 
General Biological Features of the Flora. 
The flora of the patanas as a whole is composed of plants 
which, generally speaking, present characters which tend to 
reduce transpiration and to protect delicate parts from the 
injurious effects of intense illumination: broadly speaking it 
may thus be regarded as a “ Xerophyte-Association" in Warming’s 
sense (35) In the case of the Uva patanas below 4500 feet, the 
conditions which determine the characteristic features of the 
flora are, briefly, intense illumination, the heating effects of the 
rays of a vertical sun, and a comparatively dry season of eight 
months' duration, during six months of which a drying wind 
blows constantly over the area and the sky is usually unclouded. 
The evaporation from the surface is therefore intense—a fact 
whieh must have a considerable influence upon the vegetation 
of a district which has little standing water, and but little soil 
by whieh absorbed water may be retained, and which therefore 
depends for its water-supply upon dew and rainfall; aud the 
latter, as we have already seen, is, during the dry season, 
comparatively small in amount; and what little there is, by 
reason of the undulation of the country and the hardness of the 
surface, tends to run off rather than be absorbed. Therefore 
the supply of water to the roots is small, and the necessity for 
the reduction of transpiration imperative. 
Above 4500 feet the climatic conditions are widely different, | 
as has already been pointed out. The rainfall is Jarge and 
almost evenly distributed over the year and is accompanied, 
especially at bigher elevations, by dense fogs and heavy clouds 
which obscure the sun’s rays usually for a considerable portion 
of each day *. The rate of evaporation from the surface and 
the periods of intense illumination must therefore be considerably 
less than on the Uva patanas; and further, the soil always 
retains considerable quantities of water. Nevertheless, plants 
with marked xerophytie characters predominate here as at 
lower elevations, a fact which is at first sight somewhat surprising. 
These humus-patanas at 5000 feet aud upwards, existing under 
a warm temperate climate, may be compared with the moor- 
and marsh-formations which are particularly characteristic of 
temperate climates. It is well known that the plants constituting 
such formations commonly present marked xerophytie characters, 
* See pp. 314 and 332, 
