44 DISEASES OF DECIDUOUS FOREST TEEES. 



Fomes nigricans. While there are no signs of pores or other struc- 

 tures which would enable one to definitely say that these black 

 masses are undeveloped sporophores of this fungus, the writers are 

 inclined to agree with Lindroth that this is the case. This supposition 

 is strengthened by the fact that wherever these black masses occur 

 on birch trees the characteristic decay of the wood usually caused by 

 Fomes nigricans will always be found. Attention should be called to 

 the very frequent appearance of these sterile masses a form of 

 growth, so far as known to the writers, which has not been known for 

 any other wood-rotting fungus. 



DISEASE CAUSED BY HYDNUM ERINACEUS. 



The coral fungus (Hydnum erinaceus Bull.) produces a white rot 

 of many deciduous species, chiefly of oaks. It has been found abun- 

 dantly on both the red oak (Quercus rubra L.) and white oak (Q. alba 

 L.), where its large white fruiting bodies form very conspicuous 

 objects (PL VII, fig. 2). 



The fungus enters the trees very much as do the other wood-rotting 

 fungi, growing from branch stubs into the heart of the tree. It like- 

 wise gets in through the tunnels of the oak borer in the same manner 

 as does Polyporus obtusus. The diseased wood in its final stages is 

 soft and mushy, so that when squeezed considerable water flows out. 

 Trees in an advanced state of decay have numerous large holes in the 

 heartwood, which are filled with masses of light yellowish, fluffy 

 fungous mycelium (PL VII, fig. 1). During the early stages of the 

 disease the heartwood of the oak turns lighter in color, and the more 

 rapid destruction of the wood between the medullary rays is very 

 characteristic of this type of disease. As the disease progresses, the 

 wood becomes spongy and is practically wholly destroyed, so that 

 cavities such as have been referred to form; indeed, the entire heart 

 of the tree may be destroyed, leaving but a hollow shell consisting of 

 sapwood. 



The white rot caused by the coral fungus can be recognized by the 

 very wet, soggy nature of the diseased wood. The fruiting bodies of 

 the coral fungus form on broken trunks and on standing trees, issuing 

 frequently from the holes of the oak borer. They are snow-white in 

 color, anywhere from 1 to 10 or 12 inches in diameter, and almost 

 spherical in shape. They may appear singly or in groups. The mass 

 of the sporophores is fleshy, and drops of glistening fluid frequently 

 exude over the entire surface of the top. The top surface is more or 

 less roughly hairy. The bulk of the sporophore consists of an exceed- 

 ingly large number of white teeth, or spines, bearing the spores. 



Very little is yet known as to the exact distribution of this fungus 

 and of the host trees which it attacks. Judging from the number of 



149 



