. Chestnut blight. Chestnut blight; Chestnut. 576 Bulletin 347 • Development of pycnidium.—The pycnidial stage usually appears on the cankers in three to six weeks after inoculation. The very earliest stages in the development of the pycnidium are not readily found and studied in the bark, but when the ftingus is grown in Van Tieghem cells in drops of agar the process can be easily observed under the microscope. At room temperature it begins in less than a week, in the following manner: At a certain point on a hypha, short cells are formed by the laying down of new septa. These cells increase
. Chestnut blight. Chestnut blight; Chestnut. 576 Bulletin 347 • Development of pycnidium.—The pycnidial stage usually appears on the cankers in three to six weeks after inoculation. The very earliest stages in the development of the pycnidium are not readily found and studied in the bark, but when the ftingus is grown in Van Tieghem cells in drops of agar the process can be easily observed under the microscope. At room temperature it begins in less than a week, in the following manner: At a certain point on a hypha, short cells are formed by the laying down of new septa. These cells increase in diameter and in amount of contents and each one sends out short septate branches (Fig. 92, a and b),. Fig. 92.— Development of pycnidium a and b, Very earliest stages observed in Van Tieghem cell cultures c and d, Cross sections of pycnidium on agar before the beginning of the cavity e, Cross section when the cavity first becomes apparent the individual cells of which in turn put out other short branches, until the whole structure has the appearance of a witches' broom. Other hyphas, and more distant branches of the same hypha, grow toward it and mingle with its branches. This tangle of hyphae soon becomes so dense that a surface view does not show what is occurring oh the inside, and later stages have to be studied from serial sections after imbedding, sectioning, and staining. Cross sections at this time and for some days later show that the mass is merely an increasing solid ball of hj^hae, which are all alike and densely interwoven but not anastomosed in any way (Fig. 92, c and d). A little later the hyphse at the center appear. 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 1906-1960
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