161 



X. Statistics and Distribution of North American 



Lichens 



BY HENEY WILLEY, NEW BEDFOED, MASS. 

 [Bead before this Society, October dd, 1873.] 



An attempt at presenting the statistics and the geographical dis- 

 tribution of the Lichens of Xorth America, mnst necessarily be 

 imperfect, owing to the fact that but a small portion of the conti- 

 nent has been thoroughly explored in search of Lichens; so that 

 new species may be expected to occur, even in the more familiar 

 districts, while considerable accessions to our knowledge may be 

 expected in those which have, as yet, been hardly visited by the 

 Lichenist. The present attempt, therefore, is offered only as an 

 approximation to exactness. 



In my " List of North American Lichens" as known at the com- 

 mencement of 1872, there were enumerated 808 species and sub- 

 species, some being ranked as species, which will hereafter, prob- 

 ably, be reduced to varieties. The additions and corrections since 

 made to that list (which are given in an Appendix to this paper) 

 swell the total to 823, subject to the same reservation in regard to 

 species and varieties. This estimate does not include a considera- 

 ble number of species collected but not described or published; 

 with the addition of these and other discoveries which may be 

 made, the whole number of North American Lichens may finally 

 reach between 850 and 900 ; the Avhole number of Lichens at pres- 

 ent known and described being from 1,500 to 2,000, and of Lichens 

 occurring in Europe, about 700. New species are being constantly 

 published, but the title of many of them to rank as such may well 

 be doubted, as it depends to a great extent, on minute chemical dif- 

 ferences, as to the value of which Lichenists are not agreed. 



Of the five Tribes into which Lichens are divided, according to 

 the arrangement of Professor Tuckerman in his " Genera Lichen um,'' 



BUL. BUP. 80C. NAT. SCI. (21) OCTOBER, 1873. 



