INJURIOUS INSECTS, FUNGOUS DISEASES, ETC. 187 



are thus parasites which obtain their nourishment by the 

 breaking down of the cells of the plants on which they exist. 

 As affecting shade-trees the fungous diseases are not so 

 serious as the injuries by insects. Very few wood-rotting 

 fungi are capable of entering an injured tree and beginning 

 growth. Nearly all gain lodgment in wounds, grow in these 

 and rot the wood. Fungous diseases, therefore, are usually 

 the result of some form of neglect, and it is the preventive 

 measures rather than the cures that count for most in main- 

 taining the health of trees. The various types of fungi 

 will therefore be mentioned only briefly. 



WOOD-DESTROYING FUNGI 



The most familiar fungi are the shelving or bracket 

 forms seen on dead or decaying trees. These shelves or 

 brackets are the fruit bodies, which on maturity liberate 

 millions of spores for the reproduction of other plants. The 

 spores, which are unicellular, microscopic bodies correspond- 

 ing to the seeds of higher plants, are scattered by the wind 

 and find lodgment in wounds of trees, where they begin to 

 sprout. They grow unseen for a long time by threadlike 

 roots called hyphae which bore through and between the cell- 

 walls forming a mass of white meshes called the mycelium. 

 This spreads through the heart of the tree, rapidly disinte- 

 grates the wood and causes it to rot. 



When the mycelium has spread over a large feeding area 

 and has stored reserve food it can then grow out through a 

 wound or old knot-hole and form the bracket fruit body. 



False-Tinder Fungus {Pyropolyporns igniarius (Linn.) 

 Murrill) (Fomes igniarius (Linn.) Gillet). The fungi which 

 are responsible for the decay and destruction of the heart- 

 wood of various broad-leaf trees are quite numerous. They 



