Reconquest of the Water 
Willows whose branches have drifted down stream 
are also very useful, for by judicious planting of certain 
kinds the channel can be kept in its place, as indeed 
has been done on the Mississippi. 
Unfortunately in many of our rivers the water is 
polluted by drainage ; in such cases one often notices 
the long waving locks of a green Alga Cladophora, often 
18 inches or 2 feet in length. These slimy masses 
are detested by the fisherman, who still infrequently 
catches a trout or grilse in some of these streams. 
After a heavy flood they seem to disappear, probably 
because the shingle stones rubbing against one another 
rub them off, but they soon grow again. 
In very badly polluted streams, the whole of the 
bottom and everything in the water is often covered by 
dirty white waving tufts, which have a slimy and horrible 
appearance, This is a fungus, Apodya lactea, and is a 
sure sign of pollution.” 
The Clyde below Glasgow, the Thames below London, 
and other city rivers are inhabited by masses of bacteria, 
which, however, purify the water and disappear as soon 
as all the organic matter has been digested by them. 
Such pollution is of course a waste of valuable organic 
matter and dangerous to mankind. It is difficult to under- 
stand how figx withstand such poisonous waters at all. 
A trout was discovered a few years ago apparently 
trying to mount the steps at the Broomielaw in Glasgow. 
Some kindly person put it in a bucket of fresh water, 
and it was taken to the police station, where, however, 
it died in spite of every care and attention. 
1 Webber. 2 Bonnier. 3 Henslow, Freidenfeldt, Massart. 
4 Wylie. 5 McCallum.  ° Oliver. 
7 Frith and Schroter. §® West. ® Lyons. 
and " Geographical Journal, March 1900 and September 1902. 
18 Turnbull. 
139 
