. Textbook of botany. Botany. PLANT DISEASES 375 weeks after flowering. The branches are at first slightly swollen, then they turn dark brown, and soon the tissues shrink and wilt conspicuously (Fig. 209). If it is not checked at this time, the disease will extend into adjacent tissues, and may readily be carried by insects to other branches and to neighboring trees. It is especially likely to be spread by insects just after a rain, because at such times a gummy substance is excreted on the surfaces of diseased branches, in which substance are countless living bacteria. The bacteria live throu
. Textbook of botany. Botany. PLANT DISEASES 375 weeks after flowering. The branches are at first slightly swollen, then they turn dark brown, and soon the tissues shrink and wilt conspicuously (Fig. 209). If it is not checked at this time, the disease will extend into adjacent tissues, and may readily be carried by insects to other branches and to neighboring trees. It is especially likely to be spread by insects just after a rain, because at such times a gummy substance is excreted on the surfaces of diseased branches, in which substance are countless living bacteria. The bacteria live through the winter in the diseased tissues, and in the fol- lowing spring when the tree resumes its growth they may infect the living tissues of the tree or may be carried by insects to still other plants. The bac- teria also live in cankers on vari- ous parts of apple trees, and these cankers are prolific sources of new infections. The only means known for controlling the disease is the cutting out and burning of dis- eased branches as soon as they are discovered. An infected branch must be cut at some distance below the place where the disease is evident, be- cause some of the bacteria are usually present below the darkened portions. Great care must also be taken to see that the pruning knife or saw does not come into contact with the diseased tissues, for in that case the cutting tool itself will carry the disease from tree to Fig. 209. — A branch of an apple tree attacked by the fire blight. Notice the character- istic appearance of the younger portions, which look as though they had been 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 Allen, Charles E. (Charles Elmer), b. 1872; Gilbert, Edward Martinius, joint author. Boston, New York [etc. ] D. C. Heath & co
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1917
