IV 



Preface 



The directions in the introductory chapter are designed 

 to help the teacher in getting material for study ; they are 

 not intended for the pupil, although the figures should be 

 helpful in enabling the teacher to show the class what to 

 look for in the case of the microscopic specimens. 



In the preparation of a few of the chapters valuable 

 assistance has been rendered by Mr. Albert F. Conradi, 

 while the drawings have been made by Mr. Robert A. 

 Cushman. The authors are also under great obligations 

 to Professor J. H. Gerould of Dartmouth College, who has 

 kindly read the proof, and made many valuable sugges- 

 tions for the improvement of the Guide. 



C. M. W. 



New Hampshire College of 



Agriculture and Mechanic Arts, 



Durham, August, 1902. 



