Repository: UIHistories Project: Board of Trustees Minutes - 1880 [PAGE 76]

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74 tartaric, citric malic and muric acids and albuminoid substances into carbon dioxide, butyric acid and hydrogen, whenever and wherever the conditions permit. Should this prove to be the case, it would not necessarily, if presumably, invalidate its active agency in producing the disease of the pear and apple tree; but it might render less hopeful the discovery of preventive treatment. So far as my observation goes, the allied organism found by myself in specimens sent me from Michigan of peach tree afflicted with the "yellows," is, in form and size, very similar to that of the pear blight; but, according to my own measurements and those of Dr. H. J. Detmers, who possesses a magnificent microscope furnished with the very best of Tolle's objectives, the bacteria of the peach yellows is, in its characteristic form, one-thousandth of a millimeter in transverse diameter (the same as that from the pear) and three and a halfthousandths of a millimeter long; hence, slightly longer than the pear organism. (Pear, .0000394 inch by .000118 inch; peach, .0000394 inch by .0001377 inch). The peach organism is more commonly more than two-jointed, under the sharpest definition appearing four-jointed nearly as frequently as two. Neither of them is Bacterium tenno. The most conspicuous change that can be observed, by the aid of the microscope, in the tissues affected with the blight, is the disappearance of the stored starch. The cell walls are not dissolved or altered, in any way, except by the staining, which sometimes takes place through oxidation, in the later stages of the disease. This is an important point, and though at variance with many published statements, has been established by numbers of microscopical observations devoted to this special problem. If there be any exception, it is confined to the thin walls of very young cells, which soon shrink, and become by drying much distorted. But unless the bacteria do dissolve the cellulose of the cell wall sufficiently to make a passageway for themselves, it is impossible for them to gain entrance to such cells as they infest in their adult form. So it must be likewise impossible, in the same condition, for them to spread through tissues as we find them doing. They are assuredly not carried in the circulation of the fluids of the tree; where this is most active they are not found at all, and their slow dispersion from the point of beginning, in all directions through the starch-bearing cells, is too uniform for such interpretations. It is also readily enough proved that the tissues primarily affected by blight have no open pores in their cell walls, such as occur in those of older wood, etc.; neither are there ducts or other channels for their passage. The circulating fluids are filtered most thoroughly in their passage through the walls of each cell; it is impossible for solid particles large enough to be seen by our best microscopes, to pass through the plant tissues; The speculations often made, of ordinary spores of fungi being absorbed by the roots and carried by the watery currents in the plant, are wholly erroneous. Any tyro in microscopy can disprove the toocommon assertions of this kind. Accepting *Nageh's theory of the molecular construction of the cell wall, we can only understand how the organisms pass from cell to cell in their deadly work, by supposing their germs are less than

* Sachs' Text-Book of Botany, Eng. Trans., p. 588.