54 THK WHITE PINE. 



matter, as much sunlight as the plants will en'dure without wilting, a fairly low temperature, and 

 an abundant supply of fresh air. Mr. J. Dawson, of the Arnold Arboretum, suggests watering 

 the young plants from below, so as to avoid wilting the leaves, as a means of prevention. Other 

 suggestions will be found in recent literature of the subject, practically in the reports of various 

 agricultural experiment stations. 1 



A disease which attacks the trunk of the tree, at various ages, is very prevalent in pine 

 forests, and occasions the condition known among lumbermen as "punky pine." A diseased tree 

 can frequently be recognized by its having one or more knots with a rough, irregular contour, at 

 a considerable height above the ground, commonly conspicuous by a considerable outflow of resin. 

 These seem to result from the breaking off of branches, followed by gradual decay at the place 

 where they have separated from the tree, in such a way as to admit water into the trunk, the 

 opening being afterwards partially covered by subsequent growth of the tree while decay is going 

 ou inside. 



Upon examining the wood of such a tree, it is seen to be discolored and in various stages of 

 decay, the diseased condition extending inward from the knot hole, and both upward and 

 downward from it in the trunk. By inspecting logs cut from such trees, it will be noticed that 

 the decayed portion may have filled up the center, making a rotten heart; or it may follow the 

 rings of growth for some distance, midway from the center to the periphery; or it may be still 

 nearer to the surface, its position and extent being very variable and following no recognizable 

 rule. The parts diseased are utterly worthless, though boards containing a greater or less amount 

 of wood thus affected are common in the market. Microscopic examination shows that the wood 

 is penetrated by the filaments of a fungus, and that the elements of which the wood is made up 

 have been greatly altered, and to a considerable extent decomposed by its action. 



Continued observation in the pine woods of Michigan, in different years, does not so far justify 

 the reference of this disease to any single species of the various fungi found growing upon the 

 trunks and logs of decaying pine trees. But whatever the species, one or several, concerned in 

 producing or hastening the condition described, the general facts, as stated above, appear to be 

 that the disease finds its way where the separation and decay of a branch presents a favorable 

 place for the entrance of water and the spores of fungi, and that it spreads so extensively in the 

 trunk as to entirely ruin large and valuable trees. 



In our natural forests there is, of course, neither remedy nor prevention, but in artificial culti- 

 vation careful and seasonable pruning would doubtless be the most effectual preventive, since, if 

 properly performed, the wounds left by the removal of branches would soon be grown over and 

 there would be no further danger from this source. 



KXPLAXATIOX OK PLATE XII. 



1. Agaricus melleus, cluster of youug sporopliores.' 



2. Agaricus melleus, larger sporopkore with root-like organ of attachment. 



3. Root of spruce tree invaded by mycelium of Agaricus melleus; rhizomorph of same fungnn ou the right. 

 4-6. Fragments of pine wood showing the destructive action of Agaricut melleus. 



7. Stump of White Pine attacked by Polyporus annosus ; the heart is still sound, but is surrounded by decayed 



wood and spots filled with masses of resin. 

 S. Wood of Norway Spruce in early stages of decay occasioned by action of Polyporus annosus; the white areas 



have become delignified, and the wood elements composing them are soft and easily separable. 

 9. Wood elements of Norway Spruce isolated and showing the mycelium of the Polyporus annosus. 

 10. Fruiting hyphiu and spores of Polyporus annosus. 



KXPLAXATION OK PLATE XIII. 



1. Stump of Norway Spruce, with a sporophore of 1'olyporits annosus several years old; the inner portions of the 



stump wholly decayed. 



2. Roots of a diseased spruce tree, with numerous small sporophores of Polyporus annosus attached. 



5. Stump and part of root system of a young pine tree killed by the action of Polyporns annosus, the sporophoros of 



which have grown entirely around the base of the trunk. 



4. Mature sporophore of Polyporim annosus seen from below, showing the porous spore-bearing surface. 

 .5. Mature sporophore of Polyporus annosux from above, showing the velvety upper surface and concentric bands. 



6. Mature sporopbore of 1'olijporun aiinosiit in section. 



T. Mode of infection; where the smaller diseased root crosses the larger one, the mycelium of the Polyporus annosus 

 has penetrated the latter and spread in both directions for some distance. 



1 Cf. Atkinson, Cornell Univ., Agr. Exp. Sta. Bull. 94, 1895. 



