Papers in the Biological Sciences


Date of this Version



Transactions of the Microscopical Society (1905), pp. 19-102


This work was also accepted as Dr. Clements' Ph.D. dissertation.


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, investigators 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 assigned to one or another of the physical factors, and others have been ignored entirely. In no case have they been carefully measured. 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.

Three objects have been kept clearly in mind:' (I) To correlate in a definite way the histology of leaves with the measured physical factors of their habitat i (2) to determine the kind and amount of modification taking place in the leaves of the same species in different habitats i (3) to throw light upon the plasticity of different species and genera. This investigation was suggested by Doctor Frederic E. Clements, under whose direction it has been carried on. Grateful acknowledgment is here made for helpful suggestions, and for the facilities offered by the Department of Botany at the University of Nebraska, and at the Alpine Laboratory, Minnehaha, Colorado.

I. Introduction | II. Historical | III. Physical factors | IV. Typification of Endemic Species: Hydrophytic Types, Mesophytic Types, Sciophyta, Heliophyta, Xerophytic Types | V. Discussion of Polydemic Species: Hydrophyta, Mesophyta Sciophyta, Mesophyta Heliophyta, Xerophyta | VI. Grouping of Polydemic Species | VII. Summary | VIII. Bibliography | IX. Explanation of Plates | X. Index