. Black rot, leaf spot and canker of pomaceous fruits. Black rot; Leaf spots; Canker (Plant disease); Apples. Black Rot, Leaf Spot, and Cankep of Pomaceous Fruits 6g So far as has been determined, the process of formation is similar on different substrata. The earlier stages are more accurately followed in agar cultures than on any organs of the host plant. The writer's obser- vations have been made by examining petri-dish cultures under the low power of the microscope and by the use of prepared slides from such cultures. The material was prepared as follows: Pycnospores or hyphal threads were
. Black rot, leaf spot and canker of pomaceous fruits. Black rot; Leaf spots; Canker (Plant disease); Apples. Black Rot, Leaf Spot, and Cankep of Pomaceous Fruits 6g So far as has been determined, the process of formation is similar on different substrata. The earlier stages are more accurately followed in agar cultures than on any organs of the host plant. The writer's obser- vations have been made by examining petri-dish cultures under the low power of the microscope and by the use of prepared slides from such cultures. The material was prepared as follows: Pycnospores or hyphal threads were planted in the center of agar plates, and, as the hyphae developed, pycnidia appeared in more or less definite concentric rings. In this way the oldest pycnidia were nearest the starting point, whereas the youngest were found near the margin of the culture, the stages between. FlG. 23. DEVELOPMENTAL STAGES OF THE PYCNIDIUM A, Early stage in pycnidial development. The hyphas have become closely septate, are broadened, and are beginning to tangle. B, Early stage in the process, showing the origin of hypha? which enter into the pycnidium. Some come from adjacent hyphas, others arise from cells of the threads in the immediate tangle. C. Early stage. Branching of hypha, preliminary to coiling and twisting as in D and F. D, Early stage. Twisting of hyphae about one another. E, Early stage, showing symohyo- genetic and meristematic tendencies in pycnidial formation. F, G, H. More advanced stages in the process of pycnidial formation the two being intermediate. Blocks of agar were cut out from the dish, fixed, and imbedded in paraffin. A single section frequently includes a gradual series of the several stages, from the very youngest to the more mature structures. The sections were made both perpendicular and parallel to the surface of the agar, the second method proving the more satisfactory. The young pycnidium as it occurs in agar appears to be made up of a closely tangled mass of
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectblackro, bookyear1916
