THALLOPHYTES 



59 



Perhaps the best definition of the first group (Phycomy- 

 cetes) is that it includes all true Fungi in whose life-histories 

 neither asci nor basidia appear. 



39. Lichens. Lichens are very commonly observed 

 plants, forming splotches of various colors on tree trunks, 

 rocks, old boards, etc., and growing also upon the ground. 

 They may resemble in- 

 crustations on these va- 

 rious supports ; or they 

 may have very definite 

 flat and lobed bodies 

 that are not attached 

 throughout to their sup- 

 ports (Figs. 44 and 45) ; 

 or they may have slen- 

 der, branching bodies 

 that are erect, hanging, 

 or prostrate. The so- 

 called " reindeer moss" 

 is an erect, branching 

 lichen common in north- 

 ern latitudes ; and in 

 certain mountain re- 

 gions trees are fre- 

 quently thickly covered 

 with the hanging lichens 

 (Fig. 46). 



The most important fact about a lichen is that it is made 

 up of two very different plants, a fungus and an alga ; but 

 these two are so closely associated that they seem to belong 

 to a single body (Fig. 47). In fact, a lichen is a parasitic 

 fungus that obtains its food-supply from certain Algae, and 

 in doing so inwraps the Algae completely. Apparently the 

 Algae are not injured, and in fact their position in the midst 

 of a moist, sponge-like body is very favorable for their work. 



FIG. 46. A hanging and profusely branching 

 lichen. After SACHS. 



