JOSSEEYN BOTANICAL SOCIETY 



9 



Geographical Distribution of Lichens in Maine. 



Dr. Iv. W. Riddle. 



[Abstract.] 



The problem of the geographical distribution of lichens is 

 complicated by the peculiar nature of the lichen-thallus, or 

 vegetative body. Investigation has shown that this is made 

 up of fungus filaments growing in association with the cells 

 of some alga. The so-called fruit of the lichen is in reality 

 the fruit of its fungus-component only. When the spores of 

 this are scattered they must meet with the cells of the particu- 

 lar alga to which they are adapted, in order to develop into 

 a new lichen. This introduces an element of uncertainty. 

 To avoid this, the lichen has additional means of reproduc- 

 tion by a direct or modified method of fragmentation of the 

 parent-thallus, each piece so formed developing a new lichen. 

 On account of the extensive use of this method, and on 

 account of their adaptability and resistance to unfavorable 

 conditions, lichens are widely distributed. Many of the 

 species, however, are more or less confined to definite life- 

 zones, as are the higher plants. 



In Maine there are four chief geographical regions, from 

 the point of view of lichen distribution. The first is a boreal 

 region, best represented in the conifer forests of northern 

 Maine. The second region is a transitional one, forming a 

 broad belt across the middle of the state, and having a lichen 

 flora made up of both boreal and austral elements. The 

 third region is the sandy country south of Portland, and is 

 essentially austral in its character. But probably the most 

 interesting region of all is the exposed rocky coast from a 

 point above Portland, north to Eastport. Most of the char- 

 acteristic boreal lichens occur, also, in this coastal region. 

 Some of these (e. g., Usnea longissima), are found in the 



