THE LK'HEXS 



stones; while fruticose fnnns grow upmi the, ground or liung 

 fr(jiu bnuiclies of trees. Illustrations of tin' latter group ai-e 

 the reindeer moss {^VhiJ<Dii(i i-iuiij/fcrini/ ) and other cladonias 

 (Fig. li-to), and the bearded 

 moss (^Lhnvii bdrlmiti'). 



In sections or carefully 

 made dissections of a lichen 

 body usually the fungus is 

 seen to compose the outer 

 covering for the whole bod)-. 

 The alg:e are A\'ithin, and 

 often closely wound about 

 by the hypliie of the fungi 

 (Fig. 194), ^^'hieh absorb 

 food from the cells of the 

 algae. 



The fruiting cups usu- 

 ally resemble some of those 

 of the aseomycetes. AVithin 

 tlie base of the cup in most 

 lichens the fungal liyphaa 

 form asci and aseospores, as 

 do many aseomycetes. These 

 spoi'i's belong to the fungus. 

 The algal part of the lichen 

 when it is a one-celled alga 

 like Plcuroi-occuH reproduces 

 hj division, as aa'c have al- 

 ready found that it does in 

 the green algae. This repro- 

 duction of the alga occurs 

 quite independently of the 

 reproduction of the fungus. 



229. Economic importance of lichens. Probably the greatest 

 economic importance of lichens is found in their relation to 

 formatiim of soils. Any freshly bared rock soon becomes the 



. 1'.12. X detail of a small piece of 

 Usnca barbata 



The braDC'lies bear the fruiting cups, and 



branches may also grow from the cups. 



The open sides of the cups are shown in 6, 



and the reverse surfaces in c 



