Osmotic Concentration and Water Relations in the Mistletoes, with Special Reference to the Occurrence of Phoradendron californicum on Covillea tridentata

Abstract

It should be the function of the ecologist to express the phenomena of distribution in terms of the morphology and physiology of organisms on the one hand and of the geological history and physical factors of their environment on the other. In attempting to fulfill this function and to simplify the presentation of his results by the formulation of generalizations, the worker will inevitably encounter many exceptions to codified rules. These exceptions can not be permanently disregarded. They must be rechecked to determine whether they are apparent or real. If they can not be harmonized with the formulated laws, the laws themselves must be modified. It is often the discovery of the exception which ultimately results in the establishment of the soundest generalization. The purpose of the present paper is to consider certain peculiarities of the host relations of the desert mistletoe in their bearing on generalizations which have been drawn concerning the osmotic concentration of the tissue fluids of parasitic plants. The desert mistletoe, Phoradendron californicinm Nuttall, is widely distributed in the arid southwest, having been reported from Nevada, Utah, Arizona, California, Lower California and Mexico. The list of host families and species 1 includes