SAP-ROTS OF SPECIES OF DECIDUOUS TRKES. 



57 



trunk. The forest fire may not seem to have injured the tree at the 

 time, although the heat may have been sufficient to kill the cambium 

 layer over a considerable area. The bark over such areas dries out 

 and cracks, and it is in such dead bark that this fungus finds a favor- 

 able entrance. Within a few months after the injury the sporophores 

 of Polystictus pergamenus are found growing on the dead bark, and 

 the decay caused by the 

 fungus extends rapidly 

 throughout the deadened 

 area (fig. 7). In almost 

 any burnt area of decidu- 

 ous forest one may find 

 many of the standing trees 

 after a year or two bearing 

 large masses of the sporo- 

 phores of this fungus. 



Polystictus pergamenus is 

 universally distributed 

 throughout the United 

 States and Canada, and it 

 is known from various 

 points in South America. 

 It grows on practically all 

 the deciduous species of 

 wood. It is very common 

 on species of oak and has 

 been collected by the writ- 

 ers on the following woods : 

 Red gum (Liquidambar 

 styraciflua L.), white oak 

 (Quercus alba L.), scarlet 

 oak (Q. coccinea Muench.), 

 red oak (Q . rubra~L. ) , black- 

 jack oak (Q. marilandica 

 Muench.), shingle oak (Q. 

 imbricaria Michx.), sugar 

 maple (Acer saccharum 

 Marsh.), silver maple (A. saccharinum L.), red maple (A. rubrum L.), 

 yellow birch (Betula lutea Michx. f.), chestnut (Castanea dentata 

 (Marsh.) Borkh.), shagbark hickory (Hicoria ovata (Mill.) Britton), 

 tulip poplar (Liriodendron tulipifera L.), black cherry (Prunus serotina 

 Ehrh.), beech (Fagus atropunicea (Marsh.) Sud worth), and willow 

 (Salix sp.). 



149 



FIG. 7. A living tree of red oak the bark of which was 

 killed by fire. The fungus Polystictus pcrgamenus is 

 rapidly rotting the sapwood beneath. 



