BOTANY OF THE CEYLON PATANAS. 461 
illumination” *, This view, the result of field observations, is suffi- 
ciently borne out by the anatomical characters, herein recorded, of 
those plants which have been available for examination. The 
conditions prevailing over the patanas situated below 4500 ft. 
appeared to be much more favourable to the existence of a pro- 
nounced xerophytie flora than those which dominate the open 
country at higher elevations. It was therefore confidently 
expected that those anatomical peculiarities which usually 
characterize plants of insolated areas would be more strongly 
developed in the members of the “dry” patana flora than in 
those from the “wet” patanas. That this is not the case is 
abundantly evident from the facts recorded above. This con- 
clusion is of considerable interest and by no means easy of 
explanation. 
It does not seem likely that the unfavourable nature of the 
climatic conditions of the “ dry ” patanas has been overestimated. 
It is rather probable that some factor in the climate of the wet 
patanas tending to the evolution of xerophytic characters has 
been overlooked or its influence undervalued. All the material 
of “ wet” patana plants examined was obtained from the patanas 
lying along the Hakgala valley, which, as already pointed out *, 
trends east and west and falls rapidly to the east. Throughout 
the prevalence of the south-west monsoon, this valley is swept 
by powerful winds from the west, whose dwarfing effect upon the 
arborescent vegetation on the upper southern slopes has already 
been alluded tot. Thus, although the air is never dry in any 
ordinary sense of the word, it is almost constantly changing and 
probably rarely approaches a state of saturation, at any rate in 
the lower portion of the valley. We are inclined to regard this 
as a factor of importance in the development of the xerophytic 
character of the flora, which, compared with that of the drier 
patanas, is certainly more marked than would be anticipated. 
In this connection sufficient importance has perhaps not been 
ascribed to the lowering of the functional activity of the roots of 
“wet” patana plants by the humic acids in the soil f. This to 
some extent renders them incapable of absorbing the moisture in 
the soil which under other circumstances would be sufficient to 
support a flora of a mesophytic type. 
* Pearson, Journ. Linn. Soc., Bot. xxxiv. (1899) p. 323. 
t Pearson, J, c. p. 332. t Pearson, /. c. p. 324. 
