Vlll 



ent from that of the older authors, such as Tuckerman and others, 

 being in a great measure the outcome of recent investigations in 

 symbiosis. For this reason it was thought advisable to include a 

 chapter on the more common phenomena of symbiosis, which, it is 

 hoped, will enable the student to obtain a better knowledge of the 

 true nature of lichens. 



Part II. treats of the special morphology of the families and 

 genera of lichens occurring in the northeastern United States. The 

 drawings (with the exception of Plate 5) were made by Mr. F. 

 Emil, under the author's supervision. Duly considering the diffi- 

 culties usually encountered in making drawings of this kind it is be- 

 lieved that they give a fairly accurate presentation of the histological 

 characters of the genera occurring in the territory. 



It is hoped that this work will act as an incentive toward leading 

 others to the more scientific methods of studying this interesting 

 group of plants. With Reinke, I wish to emphasize the necessity 

 for studying more carefully the polyphyletic origin and relationship 

 of the various lichen groups. This will, no doubt, lead to a more 

 accurate delimitation of the families, and incidentally also to a more 

 accurate knowledge of the phylogeny of other plants. 



COLUMBIA UNIVERSITY, May 31, 1897. 



