19 



It attacks young trees as well as older ones, entering the tree through 

 the root system and growing up into the trunk for sometimes 40 and 

 50 feet (12 to 15 meters) from the ground. The mycelium makes the 

 wood of the Spruce very brittle. Diseased wood is of a yellowish 

 color; it has a cheesy consistency so that it can be cut across the grain 

 with a knife quite readily and without much resistance. When dry, 

 it is readily powdered. The brilliantly colored. fruiting bodies are to 

 be found in July and August growing about the base of the affected 

 trees, more rarely on the trunks. (See text fig. 1; also PI. I, fig 1.) It 

 was found more frequently in places where the air was laden with 

 moisture — for instance, along the coast and near lakes. On many of 

 the islands which lie off the Maine coast the fungus was found to be 

 very plentiful, even to a distance of 5 miles (8 kilometers) from the 

 mainland, showing that the spores must be carried for a considerable 

 distance. One small island had some 12 trees on it, all White Spruces, 

 of which 7 had old fruiting organs of this fungus growing about the 

 bases of the trunks. 



STRUCTURE OF DISEASED WOOD. 



The wood of the Red Spruce or the Fir when first invaded b}^ the 

 mycelium turns yellow, and after a time cracks here and there as if 

 dried rapidly. A cross section of the trunk of a young Fir, made 

 about 6 feet (about 2 meters) above the ground, is shown in PI. II. The 

 large crack at the side was made in chopping down the tree; the other 

 cracks in the heartwood show plainl}^ how the wood has shrunken. The 

 structural changes which take place are as follows: Soon after the myce- 

 lium enters the wood of the Spruce the color changes and the wood 

 becomes more or less brittle. This is due to the fact that at various 

 points in the summer wood cracks appear in the walls of the tracheids 

 and extend in the spiral direction around each tracheid. The break 

 deepens gradually until it extends entirel}^ through the secondary 

 lamella up to the primary lamella. The latter remains unbroken. The 

 spiral breaks increase in number and at last the tracheid has the 

 appearance shown in PI. IX, fig. 1. There appear to be two series of 

 cracks, one extending upward from left to right, the other from right 

 to left. This appearance is due to the fact, as Hartig has shown, that 

 one sees the breaks in the walls of two tracheids at the same time. 

 Hartig mentions that these cracks all extend in a spiral direction, 

 none paralh'l to the walls. This is certainly a striking fact, and seems 

 to distinguish wood attacked by this fungus from that injured by 

 many others. It will be shown that some other fungi, Polyporus sul- 

 fureiis and a form of Polyporus destructor possibly, attack the wood of 

 the Spruce and the Yellow Pine, respectively, in a similar way. 



The spring wood has few cracks. These aic inaiidy in the 

 pits, where four radiating cracks appear in the secondary lamella. 



