WHAT ARE LICHENS ? 25 



SECTION III. 

 WHAT ARE LICHENS? 



In order to comprehend the true nature of lichens 

 it is necessary to have a correct idea of their origin ; 

 we must have some conception of their j^osition in 

 nature, of their relation to other plants. Lichens ori- 

 ginated in a manner wholly different from any other 

 group of plants. Their history of development is most 

 remarkable, and stands without a parallel in the world 

 of living things. In order to make clear this wonder- 

 ful origin and development it is necessary to enter into 

 a brief consideration of fungi and the lower algae. The 

 impatient reader may ask, "What do fungi and algas 

 have to do with lichens ? " He will soon learn that 

 without these plants lichens could not have come into 

 existence. We shall begin the discussion with algae. 



Every one is more or less familiar with the lower 

 alga2 ; they occur plentifully upon tree-trunks, fences, 

 upon flower-pots, walls and woodwork of greenhouses, 

 etc.; they form the green scum on ponds and brooks, in 

 watering-troughs, in fact, in nearly all moist })laces 

 and in water exposed to sunlight and warmth. These 

 plants are very small, the individual plant is, in fact, 

 too small to be seen by the naked eye. Several hun- 

 dred must become associated to form a minute green 

 speck. 



