380 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
Habitat .— species is very abundant at Hakinda, where 
most of my investigations have been made, and where it 
covers large areas of rock to the exclusion of other forms, 
though it is often found mixed with Lawia zeylanica, less 
often with Farmeria metzgerioides or Dicræa stylosa 
f ucoides, and only rarely with Podostemon subulatus, Dicræa 
elongata, or D, stylosa laciniata. It affects on the whole the 
most violent and rapid water of all the species, and is often 
found on the edges of waterfalls and similar places of very 
strong current. In the Nilgiris I found the var. griseum in 
very similar places, and occasionally mixed with Dicræa 
dichotoma, while in the Anamalais 1 found the local variety 
mixed with Hydrobryum lichenoides, var. Fentonii. The 
interminglingof this species with the larger plants mentioned 
usually occurs mainly at places where there is considerable 
local variation in the condition of the water, as for instance 
at a place where an eddy rejoins the main rush of the stream. 
This species, like the others with low-lying thalli, appears 
to be able to inhabit much smaller streams and shallower 
water than the large species, and is (consequently perhaps) 
found at higher levels. It goes far higher than any other 
species in Ceylon, except H. lichenoides, and is frequent 
from 1,500 to 5,000 feet, and in quite small streams. 
At Paikara in the Nilgiris it reaches nearly to 6,000 feet, and 
in the Anamalais I found it at 3,500 feet, and probably 
enough it may be found at higher elevations. In Ceylon it 
occurs in very small streams, which easily run almost or 
quite dry, but the thallus lies so low upon the rocks, and the 
leaves of the secondary shoots form so good a sponge for 
catching any water that may be trickling over the plant, that 
it is able to live so long as there is any water, and it can 
even stand a considerable period of complete exposure and 
yet revive and form new growing points if once more 
submerged. 
Dry Season A 2 ) 2 ^earance,—T\xQ appearance of the plants 
when completely exposed and in ripe fruit is very well 
shown in PI. XXXIII., but the plants there figured are 
