THE CARE OF SHADE TREES. 



135 



Fig. 1772. Polyporus betulinus (Birch shelf fun- 

 gus), showing the horse-shoe shaped shelf. 

 (After Massee.) 



pearance. Flattish, fruiting- structures form 

 on the surface of the roots, while the shelf 

 which appears on the roots and stumps re- 

 sembles a white crust or cake, nearly an 

 inch across. The upper surface of the lit- 

 tle shelf is brown, and the lower surface is 

 white. In all cases, save the Scotch pine, 

 the disease soon ascends into the stem. 

 Moreover, it is thought that mice and other 

 burrowing- animals assist in the dissemina- 

 tion of the spores. 



Remedy. — As with Agaricus melleus, the 

 shelves should be removed to prevent the 

 spread of spores, and a ditch dug- about the 

 diseased tree to prevent the infection of the 

 roots of neighboring- trees. 



2. Fungi affecting the Stems of Trees. 



(a) Heart-ivood Rots. {Polyporus sp.) 

 One of the most common objects seen in 

 parks and woods is the large shelf-like fun- 

 gus projecting^ from the trunks of both living 

 and dead trees. The various species have 

 quite characteristic shelves — e. g., the shelf 

 on the birch is shaped like horse's hoof, 

 that on the oak and willow is crispy and 

 wavy margined, while other forms may be 

 hemispherical. (Fig^s. 1772 and 1773.) 



The heartwood is usually the first region 

 injured, afterwards the sapwood. Wher- 



ever a crack or wound permits the thread 

 of the internal mycelium to get to the sur- 

 face, one or more of the shelves will be found. 

 It is by means of wounds that the mycelium, 

 produced by g-erminating- spores, finds an 

 entrance into the inside of the tree. In a 

 few years the heart of a tree may become 

 entirely rotten, but it is "usually several 

 years from the time a tree is first attacked 

 until its death." The majority of these 

 shelf-fung-i spread by means of spores liber- 

 ated from minute pores on the under sid^ of 

 the shelf ; while a few, like the root-rot 

 fungus, spread chiefly by underground my- 

 celia, "from tree to tree along- decaying 

 roots." 



Remedies. — In the case of trunk-infesting 

 forms, the fungfous shelf oug^ht to be de- 

 stroyed whenever it is seen, thereby pre- 

 venting the liberation of the minute spores. 

 All broken branches, moreover, should be 

 carefully trimmed and treated with some 

 protective fungicide, such as tar. With 

 root-infesting forms, where the mycelium 

 crawls from tree to tree by means under- 

 ground, decaying roots, it becomes neces- 

 sary to remove the cause of the spread. The 

 earth at the base of the tree may be freed 

 from all decaying roots, and all injuries 

 carefullv treated with tar. 



Fig- 1773- Polyporus sulphureus (Heart-wood 



Rot), showing the irregular and wavy 



margin. (After Massee.) 



