608 - Heredity and Evolution 



Circle well beyond the range of other plants. 

 Lichens also provide a source for several 

 dyes. These include orchil, a beautiful blue 

 dye, known since ancient times; and litmus, 

 the familiar pH indicator, used in the chem- 

 istry laboratory. 



Probably the lichens were among the first 

 invaders of the land areas in early geological 

 times. Many seem to secrete organic acids, 

 which dissolve and crumble the rocks upon 

 which they grow. Thus lichens probably 

 played a significant part in the creation of 



Fig. 31-15. Mushrooms are typical representatives of the Basidiomycetes. Note how the spores are pro- 

 duced by the basidia, which are borne upon the gills of the sporophore, or "cap." The mycelium, includ- 

 ing the button, must grow subterraneously for a number of weeks before the sporophore "mushrooms" 

 upward into the air. One mushroom may produce more than a billion spores. 



