Repository: UIHistories Project: Board of Trustees Minutes - 1880 [PAGE 68]

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66 and the earth about them. After a series of careful microscopical investigations of diseased specimens of peach limbs, leaves and roots, a thoroughly competent authority,* looking for any of the hitherto known parasitic fungi, tells us none such can be found to which the yellows may be attributed. Beturning again to the blight of pear trees, it is worthy of record that in an address before the American Pomological Society, at St. Louis, 1366, Thomas Mehan, of Pennsylvania, gave his reasons for theoretically holding that the disease is caused by fungi. He has steadfastly adhered to this opinion, and has year by year pointed out, through the columns of the Gardener's Monthly, and elsewhere,, the fallacy of other explanations, together with the apparent evidence supporting this. At his instance, Dr. J. Gibbons Hunt, of Philadelphia, examined, by the aid of the best microscopical equipments, blighted limbs of pear sent to him for this purpose. He reported the discovery of a fungus which, according to him, caused the blackening of the branches. In his communication he says: t " I t attacks the bark and outside of leaves and young fruit first, causing changes in the cells in these locations, resembling much those pigmentary cell-changes which differentiate the negro from the so-called white man. The cell contents, normally transparent, are changed into extremely minute pigment granules, which fill the cells and give that characteristic color and smell which mark the disease. Moreover, minute drops of viscid, offensive liquid come out on the surface. * * * From the cambium layer the fungus travels towards the interior of the stem, through the medullary rays chiefly, and here I find those round bodies which, in our hasty ignorance, we often call spores. The. ducts which ascend the stem are often obstructed with similar bodies and aggregated pigment granules. This is all I know about the subject. I cannot venture to name the fungus." I have thus quoted at some length this account, for, according to my observations, it is the nearest approach to the solution of the cause of the difficulty, founded upon direct observation, that had up to this time been made. Still, it seems impossible to admit the correctness of the interpretations here given. The coloration of the diseased parts does not come from pigment granules, or from anything which can be mistaken for them. As for the round bodies which might be called spores, in the interior of the stem, obstructing the ducts, etc*, I can only say nothing similar has been found by myself. The ''offensive liquid" seems to have escaped careful examination. In 1876, Thomas Taylor exhibited drawings at the Centennial Exposition, Philadelphia, showing f ' t h e effects of the chemical changes, which take place in the interior structure of the tree, under the attacks of the fungus to which this disease is due." Unfortunately,, I do not remember how nearly these drawings represented what I have observed. They have not been published; neither has the author made any claim of having*seen the "fungus to which this disease is due."

* Byron D. Halsted, in Transactions of American Association for the Advancement of Science, 1880. t Gardeners' Monthly, 1875, p. 245. X Eeport of Department of Agriculture, Washington, D. C, 1876, p. 75.