IV 



PREFACE 



ception of the difficulties involved in an attempt to prepare a Key for the 

 multitude of genera that have been proposed, many of which are imperfectly 

 known and described. Whether its usefulness will justify the labor involved 

 in the preparation of the work or not remains to be determined. Of errors 

 there are undoubtedly many, especially in the citations, as it has been 

 impossible to verify them all, and we shall be grateful to have them called 

 to our attention as found. No one can realize better than the writers the 

 imperfections of the work. In the present state of knowledge of the genera 

 of fungi, no generally satisfactory Key or system of arrangement is 

 possible. 



It is hoped that the treatment given and the illustrations in particular 

 may help to promote the study of mycology by students and amateurs, as 

 well as its progress at the hands of professional mycologists and patholo- 

 gists. If our efforts result in leading more students to become acquainted 

 with this interesting group of plants and to pursue this fertile field of 

 investigation, we shall feel amply repaid for our labors. 



The authors wish to express their obligation to Dr. J. C. Arthur for 



his kind assistance in the key to the rusts. They are further indebted to 



Miss Edith Cash for her aid in the bibliographic work, and to Mrs. B. F. 



Jordan for help in connection with manuscript and proof. 



Frederic E. Clements 



Cornelius L. Shear 



Santa Barbara 



and 



Washington 



December 1930 



