. Annals of applied biology. Biology, Economic; Biochemistry. 188 Apple Canker Ffmrjus—Leaf Scar Infection growth as in June. When a leaf falls, the tissue exposed is submitted to the desiccating effects of the atmosphere and results in the drying up of the cells exposed. The contraction of the tissue which takes place on drying results in small cracks appearing in the leaf scars, especially in the region of the soft tissue adjacent to the leaf traces. These small cracks allow the canker fungus the opportunity to enter the host, which it does very readily, before the host has had time to form
. Annals of applied biology. Biology, Economic; Biochemistry. 188 Apple Canker Ffmrjus—Leaf Scar Infection growth as in June. When a leaf falls, the tissue exposed is submitted to the desiccating effects of the atmosphere and results in the drying up of the cells exposed. The contraction of the tissue which takes place on drying results in small cracks appearing in the leaf scars, especially in the region of the soft tissue adjacent to the leaf traces. These small cracks allow the canker fungus the opportunity to enter the host, which it does very readily, before the host has had time to form a phellogen (Text-fig. 1). The small depressions between the leaf scars and the main stem hold up small quantities of water which probably aid the germination of the spores of the fungus. The tissue of the leaf base is rather looser than the normal cortex and the canker fungus grows very freely in the intercellular. Text-fig. 1. Radial longitudinal section of a leaf base showing a crack in the leaf scar and the mycelium about to enter the host. The intercellular space in the tissue below the crack affords an unimpeded entrance to the fungus, x 34. m= mycelium; = leaf trace; = intercellular space. spaces. The spread of the fungus is helped by the slow response of the host to form a limiting phellogen, and the stem soon becomes completely girdled (Text-fig. 2). The second period of infection, which takes place when the trees become active in the spring, however, is very similar in its symptoms to the autumn infection. Many tiny cracks in the leaf scar tissue are found especially towards March and April when the buds are bursting. Through- out the winter the buds gradually swell by normal growth, but the swelling is usually sufficiently slow to allow the continuity of the phel- logen to be maintained. The growth cracks, however, frequently extend to considerable depths. With the enormous increase in growth in early. Please note that these images are extracted from scan
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbiochem, bookyear1921
