Chapter XII. 



Lichens and Beetle-fungi. 



The life of a lichen. The group of plants known as lichens 

 is famihar to all observers. Some varieties are called gray or 

 hanging moss by persons who do not discriminate accurately 

 between these plants and the very different forms which are 

 rightly known as mosses. A still greater error is made in com- 

 mon speech, when the little hanging, gray, flowering plant, so 

 abundant in the south upon tree-branches, is given the name of 

 "Spanish moss." Lichens are found in a great variety of posi- 

 tions. They are exceedingly prevalent all over the world on 

 rocks, making characteristic patches on weathered clifTs, walls, 

 boulders, and pebbles, provided there be not some constant agi- 

 tation upon the surface of the rock, as by drifting sand or surf, 

 which might prevent their growth. They are seen very com- 

 monly upon the trunks of trees, usually preferring the side 

 toward the north. One characteristic lichen hangs from the 

 branches of tamaracks everywhere in Minnesota, and is some- 

 times called "old man's beard" from its gray color and thread- 

 like texture. Other varieties produce little patches on tree 

 trunks and they may be distinguished by their generally circular 

 form, by their flat habit of growth, and by their greenish, red, 

 yellow or gray color, which is very rarely a pure leaf green, but 

 varies more or less toward the other shades. 



Stone-corroding lichens. Lichens upon stones are very 

 often so firmly attached that they cannot be removed, having 

 eaten their way into the stone by means of acids which they 

 secrete for that purpose. Curiously enough, a lichen which can 

 live upon limestone is not always able to live upon sandstone, 

 because it takes a different kind of acid to corrode limestone 

 from that which eats away the quartz of a "granitic rock. A 

 great many of the lichens upon stones are not, however, firmly 



