DISTURBANCE OF VEGETATION _ tar 
islands, like the Bittern and Great Bustard which are 
their companions. 
Some lakes, again, have been ruined for the botanist 
by being usedas reservoirs. ‘Theconsiderable changes 
of level which this involves is a thing to which plants 
are not adapted, and only a few can withstand it, such 
as the Water Bistort (Polygonum amphibium) and the 
Shore-weed (Littorella uniflora), which are equally at 
home on land or in water, being able to change 
rapidly their structure and mode of life to suit change 
of environment. As compared with a lakelet with a 
natural outlet, a dam with a sluice has always a much 
reduced and usually quite uninteresting flora. 
The proximity of a large town, especially if it is a 
centre of manufacture, is a notorious factor in the 
reduction of the native flora: not only by the thought- 
less and wanton destruction carried out by its inhabit- 
ants, but more subtly by the deposition of soot, and 
by the poisoning of the air by sulphurous and acid 
fumes. The higher Cryptogams, such as Mosses and 
Hepatics, are particularly susceptible in this respect, 
and vanish along with the more delicate Seed Plants. 
Mining centres are specially destructive of plant life, 
since, in addition to other drawbacks, the soil is often 
buried under masses of excavated material containing 
poisonous substances. If there is a purgatory for 
plants, it is surely found in such areas. 
Other examples of the multitudinous ways in which 
human activities disturb and destroy native plant life 
will occur to the reader—the burning of moors in 
order to improve them as pasturage; in recent years 
the tarring of roads, which kills the pleasant wayside 
herbage and poisons the streams into which the road 
