. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. [Repiiiited from Phytopathology, December, 1937, Vol. XXVII, No. 12, pp. 1124-1142.] THE PARASITISM OF POLYPORUS SCHWEINITZII ON SEEDLING PINUS STROBUS^ Robert E. Wean2 (Accepted for publication August 24, 1937) INTRODUCTION Polyportis schweinitzii Pries, as a cause of root rot in coniferous trees, was reported by Sargent (23), in 1897, to be more destructive in the United States than in Europe. Von Schrenk (25), in 1900, stated that this organ- ism was very common
. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. [Repiiiited from Phytopathology, December, 1937, Vol. XXVII, No. 12, pp. 1124-1142.] THE PARASITISM OF POLYPORUS SCHWEINITZII ON SEEDLING PINUS STROBUS^ Robert E. Wean2 (Accepted for publication August 24, 1937) INTRODUCTION Polyportis schweinitzii Pries, as a cause of root rot in coniferous trees, was reported by Sargent (23), in 1897, to be more destructive in the United States than in Europe. Von Schrenk (25), in 1900, stated that this organ- ism was very common in our northern forests of spruce and fir. In 1933, York^ discovered P. schweinitzii causing root and root-crown decay in forest plantings of white pine, Pinus strohus L., established in 1912-1914. It is generally believed that this fungus attacks mature and over-mature coniferous trees by invasion of the roots through wounds. The penetration of root parasites into woody plant tissue has been extensively studied by several investigators (6, 11, 18, 25, 29). However, our knowledge pertain- ing to Polyporus schweinitzii is based entirely upon field observations. From this information it appears to have a wide range of coniferous hosts (2, 8, 12, 13, 21, 25, 34). It also has been reported on hardwood trees (15, 22). The writer is not aware of any published record of the ability of this fungus to enter its host directly or of infecting and injuring the living roots of seedling conifers. York's conclusion {op. cit.) that this organism is, apparently, a direct parasite and that there seems to be a close relation between the amount of infection and the pH of the soil suggested this investigation. The influence of temperature, hydrogen-ion concentration, and mineral nutrition on the 1 A dissertation in botany, presented to the Faculty of the Graduate School, Univer- sity of Pennsylvania, in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 2 The writer wi
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