PREFACE. 



This little book has been prepared for the use of 

 students in the Summer Course in Botany at Harvard 

 University. 



There have appeared within the last few years several 

 excellent text-books b}^ Sachs, Bessey, and others, in which 

 more or less space is given to a general consideration of 

 various groups of Cryptogams. Most of us who have tried 

 to combine field-work with the study of these books have 

 been met by the difficulty of recognizing plants belonging 

 to the genera spoken of. For example, to know a Bole- 

 tus at sight requires a knowledge of the distinctive char- 

 acters of the genus ; and these are not given in the books 

 just mentioned, but must be sought for in special works 

 not always easy to obtain. 



In writing this book the attempt has been made to 

 bring together in systematic form and in a convenient 

 shape such information as would enable a student to learn 

 to recognize a number of the commoner conspicuous 

 genera of Cryptogams. 



As it is thought that all who use this book will have a 

 copy of Gray's Manual, it has been deemed unnecessary to 

 include the Ferns and their allies. In the several orders of 

 Thallophytes where the genera have not been given, this 



