254 MANUAL OF TREE DISEASES 



appear to come from the soil near the base of the tree. In afl 

 cases, however, they will be fomid attached by mycelial strands 

 to the roots. The sporophores are usually large and may occur 

 as two to five overlapping shelves or as a single more or less 

 circular, expanded, toadstool-like body supported on a thick 

 stalk (Fig. 50). The center of the upper surface is depressed 

 where it is attached to the stalk. The upper surface is white 

 or yellowish, while the under surface is whitish and covered 

 with large angular honeycomb-like pores. 



Cause. 



The string and ray butt-rot of oaks is caused by Polyporus 

 Berkeleyi. The spores are borne around the inner surfaces of 

 the angular pores of the sporophores. Infection takes place in 

 wounds at the base of the tree, such as fire-scars. The life, 

 history and control of wood-rotting fimgi are discussed more 

 fully on page 64. 



Reference 



Long, W. H. Three undescribed heart-rots of hardwood trees, espe- 

 cially of oak. Jour. Agr. Res. 1 : 109-128, pis. 7-8. 1913. 



Wet Heartwood-Rot 



Caused by Hydnum erinaceus Fries 



Oak and other deciduous trees are affected by this wet heart- 

 wood-rot. White and red oaks are most commonly affected. 

 The disease is common in central United States and is some- 

 times found in other parts of the country. 



Symptoms. 



In the early stages of this decay, the wood becomes lighter 

 in color and the woody tissue between the medullary-rays is 

 destroyed. Later the entire structiu-e of the wood disappears 

 and there remains only a white soggy mass. Large cavities 



