PREFACE. 



THE present volume, the second of the series, is 

 devoted to a close study of the external features 

 of the leaves of our woodland plants, especially from 

 the point of view of the morphological characters which 

 are found to be of systematic value. At the same time, 

 I have incorporated such information regarding the 

 anatomical and microscopic structure, and the functions 

 of the typical leaf, as may enable a student familiar 

 with elementary Botany, or even the beginner, to under- 

 stand something of the marvellous powers displayed by 

 this complex machine in breaking up the carbon-dioxide 

 of the air and building it up into organic substances 

 which serve as the principal food of the plant organism. 



The leaf is the most plastic of all the organs of the 

 plant, and it is by no means sufficient for the Forest 

 student to know the mere shapes of ordinary leaves : 

 he ought to be familiar with the principal varieties, and 

 especially with the metamorphoses which leaves undergo, 

 and it is hardly too much to say that he who really 

 understands the conformation and adaptations of the 

 leaf, holds the key to the morphology of the higher 

 plants. It is for this reason that I have entered into 

 some matters which may at first sight appear foreign 

 to the purpose of the work as a whole. 



