432 MESSRS. J. PARKIN AND H. H. W. PEARSON ON THE 
and the plants which it supports have to contend against xero- 
phytic conditions. The absence of shade aggravates these 
conditions, the maximum air-temperature during the sunny 
portion of the day ranging between 120° and 138° F. * 
But probably the most important factor in influencing the 
biological character of the plants of these patanas is the intense 
illumination to which they are subjected f. 
“ Dry” Patanas.—Below 4500 ft., the rainfall during eight 
months of the year (February to October) is small and the sky 
usually unclouded. There is a total absence of shade; the 
intensity of illumination is therefore very high and commonly 
continuous from sunrise to sunset. The maximum. air- 
temperature during these eight months of low rainfall ranges 
from 156° F. (January) to 168° F. (August) {. For the greater 
part of the period a constant south-west wind, the S.W. 
monsoon, sweeps over the country, after discharging the greater 
part of its moisture on the slopes of the central ridge of the 
island which forms the western boundary of the area under 
consideration. 
For two-thirds of the year, therefore, the plants have to 
withstand conditions which favour a constant and intense 
evaporation, while the paucity or absence of soil over the whole 
area prevents a natural storage of water accessible to the roots. 
At the same time, during the remaining four months of the 
year—the period of the north-east monsoon—copious rainfalls 
occur constantly. 
The conditions prevailing on both “humus” and “dry” 
patanas would therefore lead us to expect in the plants 
composing their floras adaptations evolved to protect the aerial 
parts from the effects of intense insolation. Xerophytic 
characters are also likely to be prominent, though the conditions 
are not so extreme as to lead to the development of a flora of a 
very marked xerophytic type. Judging from the characters 
of the soil and climate of the two regions, the plants of the 
“dry” patanas might be expected to show a greater xerophytic 
tendency and a more marked protection against insolation than 
those of the “ wet” patanas. 
* Ceylon Administration Reports: Meteorology—Statistics for Hakgala, 1897. 
t+ Pearson, Journ. Linn, Soc., Bot. xxxiv. (1899), see table on p. 332. 
} Ceylon Administration Reports: Meteorology—Statistics for Badulla, 1897. 
