SAP-KOTS OF SPECIES OF DECIDUOUS TREES. 53 



by other factors that to all intents and purposes it is dying or dead, 

 with the possible exception of cases where the fungi grow on dead 

 patches of wood caused by some injury, as in the case of trees injured 

 by fire. 



SAP-ROT CAUSED BY POLYSTICTUS VERSICOLOR. 



Of all the fungi which grow upon the deciduous species of woods 

 after they are cut from the tree the most widely distributed, and in 

 many respects the most destructive, is Polystictus versicolor (L.) Fr. 

 Either singly or in dense masses its varicolored sporophores may be 

 found on any of the deciduous species in all parts of the world. So 

 far as known, this fungus is a strict saprophyte, except where it causes 

 the destructive heart-rot of the catalpa. This fungus grows univer- 

 sally throughout the United States, and probably in all parts of the 

 world. It is extremely common in Canada, Mexico, and Europe; it 

 is known from Africa to Australia, and it has been reported from 

 Japan, the Canary Islands, the West Indies, and South America. 



Polystictus versicolor is one of the most cosmopolitan species of fungi 

 known. It does not seem to have any preference for any particular 

 kind of wood, but grows with almost equal readiness, especially on 

 the sapwood, on every broadleaf species of wood (as distinguished 

 from coniferous wood) known. On account of its wide geographical 

 range and its ability to grow on and destroy so many different kinds 

 of wood, it should be regarded as the most serious of all the wood- 

 rotting fungi which attack the dead wood of broadleaf trees. ' It is 

 the fungus which destroys probably 75 per cent or more of the broad- 

 leaf species of timber used for tie purposes. Wherever broadleaf 

 species of wood are used for fencing, for posts or poles, or for any pur- 

 pose where they come in contact with the soil they are sure to be 

 attacked sooner or later by Polystictus versicolor. 



The fruiting bodies of this fungus are extremely variable, depending 

 upon the kind of wood upon which they grow and upon the conditions 

 under which they develop. The sessile sporophores may grow singly 

 or, more usually, many of them together, forming a series of closely 

 overlapping shelves. As just indicated, 'they are readily recognized 

 by the soft, hairy upper surface with bands of various colors. These 

 bands are usually white and yellow, although considerable variation 

 from both of these colors will be found. When young the sporophores 

 are fleshy, but they become tough and leathery when older. The 

 lower side of the sporophore is generally snow white, and the pores 

 are exceedingly regular and minute. The body of the sporophore 

 is very thin, rarely exceeding the thickness of heavy paper. 



In the majority of cases the sporophores form on a vertical surface 

 and s priii;:; from a broad sheet of mycelium which covers the entire 



14!) 



