FUNGI: THE LICHENS 



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fruticose lichen is the " hanging moss" 

 of the Northern States (Usnea barbata), 

 often found hanging from the limbs of 

 trees in damp or swampy woods. It 

 consists of very fine, grayish, much- 

 branched threads, sometimes reaching a length 20 

 cm. to 30 cm. or more, but usually smaller: It should 

 not be confused with the " hanging moss " (Tilland- 

 sia] of the Southern States, which is a flowering 

 plant. 



435. Crustaceous lichens. These form thin and 

 very close incrustations on rocks and the trunks of 

 trees. They are often so closely connected with the 

 rock or bark that it looks as if the latter were merely 

 painted. The minute fruit bodies are scattered over 

 the surface. The trunks of young beech or birch 

 trees are sometimes nearly covered with different 

 species of various colors. 



436. The gelatinous lichens. In the above 

 three types of lichens the fruit bcdy is stratified, the 

 algae being in a layer a short distance below the 

 upper surface. The algae present are usually isolated 

 cells resembling the alga Pleiirococcus. In the gelat- 



Fig. 237. inous lichens the algal element is more evenly mixed 

 nea barbata), with the fungus element. The algae here are often 



often called . ._ T -, 77 



hanging moss, of the Nostoc type. Calluna is an example. 



437. The work of lichens in soil building. The lichens are 

 believed to be among the most important early agencies in soil 

 making. Growing as many of them do on bare rocks where 

 scarcely any other vegetation can hold, especially on sloping sur- 

 faces, their disintegrating bodies mingle with the finely weathered 

 and disintegrated rock which lodges in crevices. Here many 

 ferns, grasses, and other plants can find a foothold and obtain 

 nourishment. The algae can also grow on moist rocks, but are 

 killed when long exposed to dry air in these situations. But when 

 the alga is surrounded by the close mat of fungus elements in the 



