ABSTRACT
Studies in plant pathology of any great practical bearing or importance are decidedly and characteristically modern. There is nothing pathological in the sudden destruction of a field of wheat by floods or locusts, but excessive moisture or the presence of a parasite may each bring about diseased conditions, and every gradation of phenomena between practical and inclusive types must be considered. The most usual injury by frost is the winterkilling of fall wheat. Sources of injury and weakness are of three kinds: unfavorable inanimate environment; unfavorable animate environment; and poor seed wheat. All types of disease mentioned thus far arise from physiological variations due to abnormal variations in the growth factors, are not transmissible, and consequently never spread from plant to plant or field to field, as do the infectious wheat diseases. In the mature wheat plant smut seems to be found only in the chlorophyl bearing parencliymatic tissues.
