276 WILLIS: MORPHOLOGY OF THE PODOSTEMACEÆ 
sea-level. The Mahaweli-ganga, as it flows round the Botanic 
Gardens, is a swift smoothly-flowing stream about 80-100 
yards wide during ordinary weather. It is subject, like other 
. mountain streams, to sudden and heavy floods during rains, 
and I have seen it rise 10-15 feet bi a day. The current is 
very swift even in the driest weather, and the water is 
always muddy, owing to the wash from paddy fields and tea 
estates on the hills which it drains. In the driest weather 
it has a pale straw colour, and in rains it becomes a thickly 
turbid -Stream, the colour being that of strong coffee mixed 
with a moderate amount of cream. The rise and fall of the 
water-level is rapid and decided ; in former years, before the 
mountains of the Central Province were so largely cleared 
of their forests for planting purposes, this was probably much 
less pronounced, and the water, too, was probably less 
muddy, and so perhaps the plants submerged in it could live 
at a greater depth. 
At Getambe, just below the gardens, the river enters a 
deep rocky gorge and becomes a furious torrent, resembling 
the Cl}' de above Cora Linn, or the Wharfe near the Strid. 
The stream is closely confined by hard steep gneiss rocks 
full of potholes, and in many places is reduced to a fraction 
of the width that it has at Peradeniya. This gorge continues 
for about half a mile to Hakinda, where it turns a corner, 
and at the same time the steep hillsides fall back a little from 
the glen, and the river widens out into a broad basin, run- 
ning among numerous small rocky islets. The current is 
still very rapid, but has less depth and force, and it is there- 
fore practicable to wade about in many places, an impossible 
feat in the narrow gorge higher up. All along the rocky 
part of the river just described the rocks are more or less 
overgrown with Podostemaceæ, wherever they are covered 
by water during ordinary weather. These plants grow only 
on places Avhere the water is in constant motion, and never 
in stagnant water. They even flourish on the rocks at the 
sides of the waterfalls, with the furious current rushing 
right over them. If the level of the water falls at any time 
