. Black rot, leaf spot and canker of pomaceous fruits. Black rot; Leaf spots; Canker (Plant disease); Apples. Black Rot, Leaf Spot, and Canker of Pomaceous Fruits hi a row of cells with dark-stained walls is seen in the leaf (Fig. 32). They are arranged in a direct line from the upper to the lower epi- dermis. This involves the palisade cells and the spongy parenchyma, the latter tissue now being composed of more densely packed, but large, cells. With the advance of the fungus this layer increases in size and number of cells until the diameter is increased over that of the normal part. An addi
. Black rot, leaf spot and canker of pomaceous fruits. Black rot; Leaf spots; Canker (Plant disease); Apples. Black Rot, Leaf Spot, and Canker of Pomaceous Fruits hi a row of cells with dark-stained walls is seen in the leaf (Fig. 32). They are arranged in a direct line from the upper to the lower epi- dermis. This involves the palisade cells and the spongy parenchyma, the latter tissue now being composed of more densely packed, but large, cells. With the advance of the fungus this layer increases in size and number of cells until the diameter is increased over that of the normal part. An additional layer of palisade cells may be developed in this region, but in a late stage the entire mesophyll becomes densely filled with large, irregularly shaped cells. The elongated palisade cells are completely changed and become isodiametric in form. The apparent stimulation results in hyperplasia and metaplasia of the palisade cells and in hyperplasia of the spongy tissue (Fig. 33). The diseased cells give a test for suberin with chlor-iodide of zinc and with cyanine-glycerin. Certain stages in the development of the leaf spot show discoloration of the epi- dermal cells up to the suber- ized layer only. Later, how- ever, the epidermal cells are affected beyond this region, as evidenced by their loss of normal size and color. It ap- pears that penetration of the temporary layer is accom- plished by the fungus invading the epidermal cells and thence advancing into the healthy tissue. At any rate the my- celium is found in the epidermal cells in this region. The alternate pro- cesses of the formation of this layer of tissue, and the subsequent invasion of the tissue beyond the suberized layer by the parasite, give rise to the concentric rings previously described. Bark.— The tissues of the normal apple stem represent the condition found in a typical dicotyledonous plant. In the center is the pith, radiating from which region are alternate medullary rays and fibrovascular bundle
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectblackro, bookyear1916
