Water Relations of the Polypody Fern, Polypodium Polypodioides (L.) A. S. Hitchcock

Abstract

Epiphytes have long been a source of interest to the botanist. Schimper well might be called the father of epiphytic ecology since his published observations (1884) have excited the interest of many botanists in this field of study. Schimper (1884) and Mez ('04) both stated that the scales of Dendropogon usneoides,3 which closely resemble those of Polypodium polypodioides, served to seize the momentary opportunity offered by a rain, and in their dry condition to absorb moisture rapidly over the whole surface of the plant body. In his study on epiphytic bryophytes, Olsen ('17) detailed the influence of the following environmental conditions: the age of the tree; the position of the tree in regard to light, rainfall and wind; the species of the tree; and the chemical composition of the substratum. Pessin ('24) made a physiological and anatomical study of the leaves of Polypodiur polypodioides. He described and attempted to explain the behavior of the leaves during desiccation. After performing experiments in which he sealed leaf surfaces petrolatum, he concluded that the under surface of the leaf lost more water than the upper, with the result that a curling of the leaf occurs. The function of the scales was thought to be both distribution and absorption of water present on the surface of the leaf. Pessin ('25) then made a more detailed study, whose purpose was to explain the distribution of the fern. From his investigations, Pessin concluded that the evaporating power of the air was the most