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LICHENS. 



THE lichens are manifestly closely related to 

 the fungi in many particulars, especially of 

 structure, and were so regarded by Berkeley, who 

 classed Fungi and Lichens together as two great 

 families constituting the Mycetal Alliance. They 

 differ from fungi in mode of growth, in their living 

 at the expense of the surrounding medium, and not 

 of the matrix, and in the production of gonidia. The 

 greater proportion of fungi are destructive, either of 

 living structure, or dead matter by disintegration, 

 whereas lichens are not destructive of the substances 

 upon which they flourish, or rather to which they are 

 attached. Moreover, lichens are usually of slow 

 growth, persistent for years, not being so prone to 

 decay. 



It is difficult, in the absence of any complete 

 catalogue of recent date, to estimate with any pre- 

 cision the number of described species ; but we know 

 them to be far less numerous than fungi or algse. In 

 1847 the estimated number of species for the whole 

 world, according to Lindley's " Vegetable Kingdom," 

 was 2400. In 1869 Krempelhuber's catalogue raised 

 the number to 5 131, and since that period a great 



