Viii PREFACE TO THE THIRD EDITION 



Chapter VIII on "Taxonomy" has been increased by seven pages 

 of new data, and the whole former text carefully revised. 



Chapter IX on "Ecology" has been newly introduced as has also 

 a Glossary of Botanical Terms. The index has been so planned as 

 to make the information contained in this book readily accessible. 



To the authors of works from which cuts were borrowed the 

 writer's thanks are due. 



H. W. Y. 



