LICHENS, 141 
shaggy and picturesque: appearance of the rocks, 
yet the object of that steady, ceaseless labour will 
one day be accomplished. And it is humiliating 
to the pride of man to find that the noble piles of 
architecture built by him as if for eternity, though 
apparently as solid as the rock out of which each 
individual stone had been hewn, and as hard as 
the famous Roman cement which had resisted 
the utmost efforts of Goth and Vandal, must 
yield in the end to the slow but persevering 
assaults of the most diminutive and contemptible 
vegetables, and be brought back again by these 
apparently feeble agents to the bosom of nature, 
out of which he had reared them with such 
labour and skill. Here, indeed, we have an illus- 
tration of that comprehensive saying of Mel- 
anchthon, ‘ The humble ones are the giants of the 
battle ;’ here we have sermons in stones, lessons 
taught us by the lifeless lichens of the perma- 
nence of nature, and the never-ceasing change and 
decadence attendant upon all the works and 
possessions of man. 
The objects which lichens subserve when they 
are: produced on rocks and ruins are thus suffi- 
ciently obvious ; but it is not so easy to determine 
their precise use when growing on trees. It has 
been asserted by some writers that so far from 
being beneficial, they are absolutely prejudicial 
