WHAT ARE LICHENS r* 37 



tion. The method of reproduction in lichens is wholly 

 different from that of fungi as well as algae. It is, 

 however, true that the spores of lichens have a close 

 morphological resemblance to the spores of certain 

 fungi, but functionally they differ widely. The spores 

 of fungi can develop into new spore-producing in- 

 dividuals, while the spores of lichens cannot produce 

 new lichens unless associated with the essential algae, 

 which proves that the fungal symbiont can no longer 

 mature independently. Some of the lichen-algae have 

 been induced to exist independently, but it is evident 

 that some cannot. Lichen-spores are simply the 

 functionally degenerate reproductive organs of their 

 fungal ancestors. 



As already indicated, fungi are essentially parasitic 

 and saprophytic. Lichens have partially or almost 

 wholly lost the saprophytic and parasitic function and 

 have acquired the power of converting inorganic sub- 

 stances into organic compounds. The thallus of lichens 

 is structurally and functionally comparable to the leaf 

 of higher plants ; fungi have no thallus, nor do they 

 have any functional resemblance to the leaves of higher 

 plants. 



Lichens also contain chemical compounds not found 

 in fungi or algae. Among these, lichenin (lichen-starch) 

 is the most important ; others are various acids (ever- 

 nic, cetraric, etc.) and bitter extracts, coloring sub- 

 stances, and other compounds as yet not well known. 



The typical reproductive organs of lichens are the 

 soredia. These are in reality miniature thalli espe- 

 cially adapted to serve as propagative organs. They 



