. A text-book of mycology and plant pathology . Plant diseases; Fungi in agriculture; Plant diseases; Fungi. 276 GENERAL PLANT PATHOLOGY As an internal determining cause, the formation of enzymes under abnormal conditions must be reckoned as causal, as well, as nutritive disturbances which produce monstrosities and the like. Having classified the chief causes of disease, a more detailed descrip- tion of these factors should be put in a form available for student use. Much of the information is scattered, and part of it is buried in foreign botanic and pathologic journals, which can be consulte
. A text-book of mycology and plant pathology . Plant diseases; Fungi in agriculture; Plant diseases; Fungi. 276 GENERAL PLANT PATHOLOGY As an internal determining cause, the formation of enzymes under abnormal conditions must be reckoned as causal, as well, as nutritive disturbances which produce monstrosities and the like. Having classified the chief causes of disease, a more detailed descrip- tion of these factors should be put in a form available for student use. Much of the information is scattered, and part of it is buried in foreign botanic and pathologic journals, which can be consulted only in the largest scientific hbraries at home and Fig. 112. -Oyster-shell scale (Lepidosaphes ulmi. After Quaintance, , Farmers' Bull. 723, Apr. 26, 1916. U. S. The chemic condition of the soil, as a determining cause of disease, may be considered from the standpoint of the normal influence of the important soil ingredients, as contrasted with the absence or deficiency of such elements. Potassium is usually found in young tissues and dis- appears in the older ones. It is associated in some way with the for- mation of carbohydrates in the plant such as starch, sugar and cellulose. The absence of potassium in-the soil causes a cessation of growth, the leaves fail to develop the power of forming starch within the greenr coloring bodies, or chloroplasts. A plant which has failed to grow for months will recover in a few days after potassium salts have been added. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harshberger, John W. (John William), 1869-1929. Philadelphia : P. Blakiston's Son & Co
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