ORNAMENTAL PLANTS SUBJECT TO DISEASE AND INSECT PESTS : Page 820

The true diseases of plants are either physiological, such as tip burn,due to over-transpiration of water during a hot wind, or parasitic.The parasitic diseases either kill by the secretion of toxins and enzymeswhich destroy plant tissues, or these toxins and enzymes cause ex-cessive tissue growth or diversion of food substances of the plant to theuse of the parasite. When the plant tissue is killed a rot, blight, or leafspot appears and when the second effect takes place the result is a gall,leaf curl, rust, or smut. The first effect, which results in the immediatedeath of the plant tissue, is of course the most harmful. Anthracnoseis a disease caused by one definite sort of fungus or parasite.