252 LICHENS 



but the braes round which it circles wear a sophisticated 

 aspect ; the fern springs as fresh here as elsewhere, but 

 the greenwood has forfeited some of its special grace ; the 

 gray crag drops as sheer from its crest as in any Highland 

 glen, but it has parted with some elements of dignity. Only 

 the other day, when strolling through a princely demesne, 

 well stocked with fur and feather, but within sound of a 

 great manufacturing city, did I hit by accident upon the 

 secret. ' Where were the lichens ? ' 



There were none. The humblest of all forms of terres- 

 trial vegetation had ceased to exist within the zone of 

 coal-smoke. That was why the wayside boulders showed 

 so dark and monotonous, and the tree stems seemed grim 

 and unyielding as wrought iron. There happened at the 

 time to be no impurity in the air ; it was a serene winter's 

 day the sun unclouded, the lift blue, a brisk nor'-west 

 breeze flying across the Clyde from the snowy Highland 

 hills. But it was easy to understand that, with the wind 

 from another quarter, or in calm, damp weather, when fog 

 broods over the plain, the atmosphere would be charged 

 with the waste products of combustion. Men, beasts, and 

 trees manage to thrive through it ; only the lowest 

 organisms succumb. 



Of course there is nothing new to science in all this. 

 Of myself I know nothing, or next door to nothing, 

 about the cellular cryptogams, but on returning home I 

 looked up a treatise on lichens by the Rev. J. M. Crombie, 

 and among the first statements that caught my eye was 

 that ' their fully developed condition is a sure indication 

 of the purity of the air.' Obviously, the lichen's im- 

 patience of coal-smoke is one of the elementary facts 

 known to every cryptogamist, but a fact acquired at first 



