WHAT ARE LICHENS ? 33 



association of a fungus and an alga, two morphologi- 

 cally distinct organisms. We shall now consider 

 somewhat more in detail the relation of lichens to both 

 algae and fungi. 



II. THE RELATION OF LICHENS TO ALG^ AND FUNGI. 



In the historical review we have already indicated 

 the varied positions given to lichens in the many sys- 

 tems of classification. Shortly before Schwendener's 

 wonderful discoveries lichens were treated as a distinct 

 class of plants, coequal in systematic importance with 

 fungi, algas and mosses. . Schwendener and his fol- 

 lowers unhesitatingly classified them as fungi. "Why ? 

 Because they looked upon lichens as fungi which were 

 parasitic upon algie* Reinke, de Bary and others have, 

 however, shown conclusively that it is not a truly 

 parasitic relationship ; as already indicated, it is an 

 association mutually beneficial, known as mutualistic 

 symbiosis. Schwendener's error was due principally 

 to the fact that he misinterpreted the relationship and 

 laid too much stress upon the spore-bearing structures. 

 There are no more reasons why lichens should be 

 classed as fungi than as algse. In fact, the eminent 

 scientist, Nageli, classified them as algae and Tucker- 

 man in his earlier writings designates lichens as " aerial 

 algae." The eminent French lichenologist, Ny lander, 

 had already recognized the double affinity of lichens 

 without realizing their true dual nature. In his sys- 

 tem of classification he begins with those lichens most 

 nearly resembling fungi, gradually proceeding to the 

 highest foliose and fruticose forms, then forming a 



