An Undescribed Timber Decay of Pitch Pine

Summary

Polyporus amorphus cannot yet be said to be a common fungus in this country since only a few collections are known. It is probable, however, that it is more common than these collections would indicate. Indications are that its range will be southern Canada, New England, and the states bordering on the Canadian line.

The fungus causes a characteristic decay of the sapwood of Pinus rigida, and has been collected also on wood of P. Strobus, P. pungens, and Tsuga canadensis.

In external appearance the decayed wood is darker in color than sound wood and is of a cinnamon-buff color (Ridgway). The spring wood is completely decayed long before the summer wood disappears. This results in the formation of concentric cavities alternating with the bands of firmer summer wood, and has suggested the name “stringy rot.”

Microscopic examination and microchemical tests establish the fact that the fungus first dissolves out the cellulose of medullary rays, then the bordered pits. The lignified structures including the ray tracheids and the vertical tracheids are then attacked and eventually (at least in the spring wood) entirely destroyed. Consequently it is believed that cellulose dissolving enzymes are produced in quantity by the younger mycelium, although probably a lignin dissolving enzyme is not entirely absent. In later stages of decay a lignin dissolving enzyme is produced in greater quantities.