. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. 1134 Phytopathology [Vol. 27 1937] Wean: Parasitism of Polyporus schweinitzii 1135 acterized by short laterals of larger diameter than those of the other series. The percentage of infection on the roots of the current season was similar to that of the low nitrogen series, but that of the older roots was similar to that of Series C at pH (Fig. 2, E). It is significant that all inoculated cultures in the various series yielded plants with less new-shoot growth an
. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. 1134 Phytopathology [Vol. 27 1937] Wean: Parasitism of Polyporus schweinitzii 1135 acterized by short laterals of larger diameter than those of the other series. The percentage of infection on the roots of the current season was similar to that of the low nitrogen series, but that of the older roots was similar to that of Series C at pH (Fig. 2, E). It is significant that all inoculated cultures in the various series yielded plants with less new-shoot growth and smaller root systems than were found under similar conditions in the controls. Fewer lateral roots, likewise, developed in the former cultures, with the exception of the 2-year-old plants of Series A. The results from pH determinations of juice extracted from the roots of both age classes of the plants showed a correlation with the shift in pH of the nutrient solution. Juices from the needles and stems, however, failed to show any substantial deviations. Infected roots (Fig. 2, K) showed injury of various degrees of severity. In some instances the mother roots bore lesions (Fig. 2, F) with large open areas of decay. In others it appeared that certain root tissues had become meristematic in an attempt to wall out the fungus. Direct infection had often taken place through epidermal and cortical cells (Fig. 3, A and B), although the typical mode of entrance appeared to be either through a lat- eral or at its base (Fig. 2, H and I). Portions of roots killed by the fungus showed a dark red discoloration of the central region (Fig. 2, J) extending upward in the mother root toward the root-crown, occasionally even into the stems. The fungus could not be isolated from tissues very far distant from the point of initial infection, even though the discoloration in the central portion of the root extended beyond such areas. Chemical Analyses.^ York (op. cit.) found upon comparing the ash
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