vi PREFACE TO THE FIRST EDITION 



would be, it would tend to confuse rather than to 

 assist the student. For this reason we do not pro- 

 fess to have mentioned all research on the subject 

 matter; indeed in some instances, the chapter on 

 Growth for example, some critics will say that too 

 much has been omitted ; we trust, however, that no 

 work of outstanding importance and requisite for 

 our treatment has been omitted. Details regarding 

 methods of experiment have been omitted since this 

 aspect of the subject more properly belongs to a 

 practical treatise. 



P. H. 



T. G. H. 



July, 1922. 



