Studies on the seasonal changes in the moisture content of western hemlock Tsuga heterophylla (Raf.) Sargent, demonstrated two moisture minima, one in the spring and one in the fall, and two maxima, one in the spring and the second in the winter. Significant differences were noted for both bark and wood moistures between good and poor sites, between seasons of the year and for the interaction between site and seasons of the year. The relative turgidity of bark from the good site was below the 80 per cent level for 95 days through an entire year. On the poor site it remained under this critical value for 123 days of the 8 months observation period. Dwarf mistletoe did not appear to affect the water economy of the portion of branches that had not been invaded by the endophytic system. However the parasite produced moisture stress in the bark at the central area of infections. An investigation of the fungi that were associated with cankered areas of dwarf mistletoe infections revealed the occurrence of twelve different species of fungi. Nine of these were Ascomycetes and three were Fungi Imperfecti. There were two undescribed species, and one species, Mytilidion decipiens Karst. had not been reported previously for North America. Preliminary tests of the parasitism of seven species indicated that one, a member of the Fungi Imperfecti, was mildly parasitic. / Science, Faculty of / Botany, Department of / Zoology, Department of / Graduate