[Reprinted from TRANSACTIONS OF THE AMERICAN MICROSCOPICAL SOCIETY, 1905.] 



THE RELATION OF LEAF STRUCTURE TO 

 PHYSICAL FACTORS 



Published under a grant from the Spencer-Tolles Fund 



BY EDITH SCHWARTZ CLEMENTS 



WITH NINE PLATES 



TABLE OF CONTENTS 



Page. 



I. Introduction 19 



II. Historical 20 



III. Physical factors 27 



IV. Typification of Endemic Species 29 



Hydrophytic Types 3 1 



Mesophytic Types 32 



Sciophyta 32 



Heliophyta 35 



Xerophytic Types 38 



V. Discussion of Polydemic Species 45 



Hydrophyta 4 6 



Mesophyta Sciophyta 48 



Mesophyta Heliophyta 5 6 



Xerophyta 64 



VI. Grouping of Polydemic Species 81 



VII. Summary 89 



VIII. Bibliography 93 



IX. Explanation of Plates 95 



X. Index 99 



I. INTRODUCTION 



The leaf, as the seat of important physiological functions of the 

 plant, and because of its modification by external factors, has long 

 been a fruitful subject for investigation. As a rule, however, in- 

 vestigators have confined themselves solely to the histology and 

 morphology of the leaf, independent of its relations to physical 

 factors. Where the latter have been considered at all, it has been 

 in a more or less general way, or undue importance has been as- 

 signed to one or another of the physical factors, and others have 

 been ignored entirely. In no case have they been carefully meas- 

 ured. The aim of the present paper has been to study the histology 

 of the leaves of a comprehensive number of species, and to take 

 careful account of the physical factors which affect leaf structure. 



19 



