INTERNAL WATER RELATIONS OF YELLOW BIRCH AT CHALK RIVER
Wood moisture was measured in the butt of healthy and decadent yellow birch trees growing on various sites in the summers of 1950 and 1952. The moisture content decreased from almost 100% in May to about 60% in late June when the leaves were fully unfolded. Wood moisture was usually 5 to 15% higher in the butt of decadent trees than in healthy trees during the 2 years of investigations. It was higher in the trunk of trees on a dry site during a wet summer and on a wet site during a somewhat dry summer.Relative turgidity in leaves was measured in mature trees as well as in leaves of seedlings growing on soils with varied moisture contents. Relative turgidity was usually less during the day. During periods of drought it decreased even during the night. Exceptions observed may have been caused by leaf absorption of dew. In young birch seedlings relative turgidity values varied between 65 and 50% in soils ranging from 100 to 70% of field capacity. As the soil wilting point was approached, relative turgidity of leaves decreased to about 35%.