On the origin of parasitism in fungi.

Abstract

Up to the present no definite explanation has been offered as to why a given parasitic fungus is often only capable of infecting one particular species of plant. This, however, is well known to be the case, for although the spores of fungus parasites germinate freely on the surface of any plant when moist, infection only takes place when the spores germinate on the particular species of plant on which the fungus is known to be parasitic. This apparently selective power on the part of the fungus I consider to be due to chemotaxis. An extensive series of experiments were conducted with various species of fungi, including Saprophytes, facultative parasites, and obligate parasites, and the results are given in tabulated form in the full paper. The chemotactie properties of substances occurring normally in cell-sap were alone tested; among such may be enumerated saccharose, glucose, asparagin, malic acid, oxalic acid, and pectase. In those instances where the specific substance, or combination of substances, in the cell-sap assumed to be chemotactic could not be procured, the expressed juice of the plant was used.