File:A text-book of mycology and plant pathology (1917) (14762213411).jpg

Identifier: textbookofmycol00hars (find matches)
Title: A text-book of mycology and plant pathology
Year: 1917 (1910s)
Authors: Harshberger, John W. (John William), 1869-1929
Subjects: Plant diseases Fungi
Publisher: Philadelphia : P. Blakiston's Son & Co.
Contributing Library: University of British Columbia Library
Digitizing Sponsor: University of British Columbia Library

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nternal. Theexternal factors of disease are the chemical conditions of the soil, as adetermining cause, also the physical character of the soil. The influ-ence of a superabundance.of water, or its absence, is important. Cli- 1 Cook, Mel T. and Taubenhaus, J. J.: The Relation of Parasitic Fungi to theContents of the Cells of the Host Plants, i. The Toxicity of Tannin, Bull. 91,Delaware College Agric. Expcr. Stat., Feb. i, 191 t. GENERAL CONSIDERATION OF PLANT DISEASES 275 matic and meteorologic conditions may be influential, when these dis-turb the normal life of the plant. Light, heat, cold, rain, dew, hail,frost, wind and lightning play an important role. The gaseous emana-tions from gas pipes, smelter works, smokestacks, including soot, dustfi;om cement works, acids, poisons, and dye stuffs, which pollute streams,all are determining causes of disease. Traumatism or mechanic injurymay be of various sorts and the effects are dependent upon the form andseverity of the injury, or wound.
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Fig. III.—Rose-chafer (Macrudaclylis subspinosiis). a. Adult or beetle; h,larva; c, d, mouth parts of same; e, pupa, /, injury to leaves and blossoms ofgrape with beetles at work. (From Marlatt in Quaintance, A. L. and Shear, C. L.,U. S. Farmers Bull. 284, 1907.) Living organisms, whether animal or vegetal, may be the cause ofdisease. All groups of animals may be considered, but the mammals,worms and insects (Fig. in) are of most importance and interest.Insect depredations of plants are notorious and insects occupy firstplace in their destructive effects on plants (Fig. 112). Various para-sitic flowering plants are known, as well, as the bacteria and fungi,for their disease-producing powers. 276 GENERAL PLANT PATHOLOGY As an internal determining cause, the formation of enzymes underabnormal conditions must be reckoned as causal, as well, as nutritivedisturbances which produce monstrosities and the like. Having classified the chief causes of disease, a more detailed descrip-tion of t

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