Causes of hemlock brownstain. Phase 3. Evaluation of the potential of hem-fir wood extractives as precursors of hemlock brownstain. (Third of six reports)
Hemlock brownstain was studied histochemically, in microscopic sections of western hemlock and amabilis fir, and chemically, using wood extractives of western hemlock. For the first time it was histochemically demonstrated that brown pigments, found in amabilis fir and western hemlock, are at least partially composed of catechin and/or epicatechin. Evaluation of nine extractives of western hemlock provided no indication that they play a significant role in hemlock brownstain. However, sap collected from western hemlock showing signs of brownstain produced browning on filter paper. Thus the composition of the sap, yet unidentified, was responsible for discolouration observed in this study.