PREFACE vii 



acknowledgment and express my regrets that many useful sug- 

 gestions could not be made use of in this brief text. I shall be 

 glad to consider any criticisms of materials or methods of pre- 

 sentation which readers and students may submit. I want to 

 express my thanks to my associate, Mr. Alwin Berger, for cor- 

 rections and additions in the botany of the book. 



U. P. Hedrick. 



New York Agricultural Experiment Station, 

 Geneva, New York. 

 February, 1925. 



