VI PREFACE TO THE FOURTH EDITION. 



these. Still, methods of cultivation and examination are given 

 in some detail. 



Dr. Williams was unable, for a number of reasons, to revise 

 and correct the book himself. The entire responsibility for 

 the present edition (including the chapters by Dr. Clinton and 

 Dr. Carpenter) rests with the reviser. 



B. Meade Bolton. 



Washington, D. C, September, 1905. 



