340 Man's Work on the Farm 



others, quite distinct from these, were to be found onlj 

 on the heath. For change in the vegetation had been 

 followed by a corresponding change both in the insect- 

 life and in the bird-life. 



Not a marsh nor a field can be drained, not a canal 

 can be cut, not a railway or even a road can be made, 

 nor a house built, without making some change, and in 

 some cases a very great change, in the vegetation of 

 the place or immediate neighbourhood. As for the 

 growth of towns and cities, that affects far more than 

 the immediate neighbourhood ; for not only is many a 

 field covered with bricks and mortar-r but the smoke 

 from the chimneys and the increased traffic on the 

 roads have their effect upon vegetation, sometimes for 

 miles round. 



When to houses are added factories, the evil influ- 

 ence is felt still more widely, and that even by lichens. 

 Lichens are such very passive-looking vegetables, so 

 little life-like, and so largely composed of mineral 

 matter, that one is apt to fancy they cannot be 

 sensitive. And they are in many respects very hardy, 

 as we have seen. But they, too, have their limits 

 of endurance. They may stand both biting cold and 

 parching heat ; but smoke kills them, especially the 

 larger leafy-looking species, such as grow on the 

 trunks of trees. They flourished formerly in the 

 woods, seven miles from Newcastle, and might flourish 

 there still, but for the change in the atmosphere, for 

 nothing else is altered. But the factories and collieries, 

 though several miles off, have polluted the air ; the ' 

 trunks and branches of the trees have acquired the 

 grimy look which they wear in cities, and all the larger 

 lichens, and most of the smaller, have been killed by 



