LICHENS LIFE'S PIONEERS 



there will soon be found on it a vegetable growth 

 that often resembles the dried bark of a tree, clinging 

 closely to the stone, and partaking of, or rather giving 

 to the stone its dominant color. In dry weather it is 

 usually hard and somewhat friable, appearing indeed 

 as if it were the dead residue from a former vegeta- 

 tion, rather than a still living plant. In damp 

 weather the tissues absorb moisture rapidly, swell up 

 and become partly or entirely green, or partly yellow, 

 red and grey, mixed with green. 



These plants, some of them so small even when 

 grouped together as to seem rather a stain upon 

 the face of the rock than a living structure, are 

 Lichens, the most widely diffused of all forms of 

 vegetation, extending from the sea-coast in the tropics 

 to the highest summits of the arctic mountains. They 

 are the pioneers of the organic world; they seize 

 upon the naked rock for their domicile, and thrive and 

 multiply where nothing else can find a foothold. 

 Nor is their life ephemeral : they retain their posi- 

 tion through the greatest drought, the highest heat 

 of the tropics, and the intense cold of the highest arctic 

 mountain summits. Though their constituent tissues 

 die, they are soon replaced in detail by new growths, so 

 that they appear immortal. The same patch of lichens 

 has remained apparently unchanged upon stones in 

 buildings for hundreds of years. Probably the life 



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