LICHENS 



97 



Lichens. 



BY DR. AND MRS. ALBERT SCHNEIDER, SAN 

 FRANCISCO, CALIFORNIA. 



You have seen, on rocks and trees 

 in wild places, certain flat, papery or 

 leathery objects of various colors, that 

 resembled you hardly know what, un- 

 less you arc a botanist. You have 

 probably seen them too on soil, ami 

 so loosely attached as to become sepa- 

 rated at the lightest touch, while some 

 on the rocks, apparently hardly more 

 than spots of color, seem almost im- 

 bedded; and on old houses and fences 

 ami in exposed situations generally at 

 all seasons. These blotches are living, 

 growing plants. They are lichens. 

 Most fascinating plants they are too, 

 because of their wide range and pe- 

 culiar mode of life. 



Sometimes rocks or large boulders 

 are so covered with various kinds that 

 they present a curiously mottled, often 

 an encrusted appearance. 



I remember hearing the driver of 

 a stagecoach say, as he pointed to a 

 well-known lichen hanging in festoons 

 from the branches of a tree, "Yes, sir, 

 that stuff up in those oaks will show 

 you how high this river rises some- 

 times." 



How much more interesting many a 

 drive would be. if we knew a little 

 more of the world about us. 



Lichens are world-wide in their dis- 

 tribution. In the extreme north they 

 form the most advanced outpost of 

 vegetable life. They are found on 

 mountain tops far in advance of other 

 vegetation, and they abound in the 

 hottest countries. They are the pioneers 

 of the vegetable world, subsisting 

 largely on wdiat the wind and the rain 

 can bring them. 



They are most frequently seen on the 

 weather side of rocks, trees, fences and 

 old houses. This fact has been util- 

 ized by explorers and trappers to guide 

 them through unfamiliar places. One 

 kind grows on the leaf of the coffee 

 plant, and one found in California 

 grows on the boxwood leaf. Both 

 probably derive some nourishment 

 from the green part of the plant, and 

 are therefore to some extent probably 

 parasitic. A few are marine, occurring 

 on rocks and rocky ledges that are 

 submerged at high tide. 



They seem to disappear before the 

 advance of civilization, and are com- 

 paratively rare in parks, near dwellings 



and along much traveled roadsides. 

 Some authorities say they are sensitive 

 to noxious gasses smoke and dust. 

 They are little affected by drought or 

 changes in temperature. During dry 

 weather or dry seasons they lie dor- 

 mant, but with the iirst rainfall they 

 change from brittleness to elasticity, 

 and the colors brighten. 



As distinguished from the mosses, to 

 which they are not related, they lack 



RAMALINA RETICULATA. 



leaves and the characteristic green col- 

 oring. They are lower in the scale of 

 plant evolution than the mosses. 



A lichen is not a single plant unit as 

 is the oak or the fern, but a composite 

 organism made up of an alga and a 

 fungus. The kinds of algae vary in the 

 different lichens. Most of them, how- 

 ever, are the simplest forms, known as 

 the single-celled algae. Most of the 

 fungi belong to the group known as 



