X AUTHOR'S PREFACE 



I desire to acknowledge my indebtedness to 

 my good friend E. A. Bessey, M.A., Ph.D., 

 Professor of Botany, Michigan Agricultural Col- 

 lege, for kindly writing the Prefatory note and 

 the subject matter on pages 29, 30, 33-38, 79 and 

 83 ; for reading the whole of the proofs and for 

 many other valuable suggestions and additions. 



To any others who have assisted me either 

 directly or indirectly I tender my best thanks. 



THOMAS MILBURN. 



(Bounty Offices, 

 Preston, July^ 1915- 



