Study of Polyporus betulinus (Bull.) Fries

1. An introductory survey is made of the distribution, uses, synonyms and ststematic position of Polyporus betulinus (Bull) Fries. 2. Parasitism is discussed. Negative results have been obtained from infection experiments; but field observations force the writer to the opinion that the fungus is a parasite. 3. From observations in Nature and in culture the type of breakdown produced in the attacked wood is classified as a red-brown cubical rot. The microscopic characters are listed following Hubert's method. The stages in decay are illustrated. 4. A brief survey of the enzyme content is made, following Buller's methods. The fungus is shown to contain a variety of ferments capable of attacking the woody tissues of the birch. It appears to belong to both the lignin-destroying and the cellulose-destroying groups of wood-attacking fungi. 5. The culture characters of the mycelium are investigated and the fungus classified according to Fritz's work. 6. Black lines are formed in culture. These are related by position with bulbils (sclerotia). It is suggested that here, as elsewhere, both are resting stages. 7. Sporophores are described in Nature and from culture. The hymenium consists of pores lined by basidia and sparingly interspersed with cystidia. These latter appear to be modified fibre hyphae. The sequence of nuclear phenomena in the basidium is traced. The period of spore discharge is determined for the species and for individual sporophores. 8. From an examination of the structure of sporophores, bulbils and zone lines it is suggested that all three are constructed on the same fundamental plan. 9. The life history of the fungus has been carried through from spore to spore in culture, in a space of three months. 10. Monospore cultures were obtained. The fungus is heterothallic. The spores were shown to fall into two groups by pairing 12 monospore colonies in every possible way. Monosporous mycelia show single nuclei and no clamp connections. The normal hyphae contain paired nuclei and bear clamp connections. 11. A bibliography of 75 titles is appended