HEART-ROT CAUSED BY OTHER FUNGI 127 



reason to suppose it is confined to those counties. The 

 parasitology and method of attack of the fungus have not 

 been worked out. The best papers on the disease are by 

 Hartig (1878), who described it under the name of Polyporus 

 mollis, Fr., and gave an account of two hundred-year-old 

 Scots pines which had been attacked l)y tlie fungus, and by 

 Schrenk (1900), who described the rot on American trees 

 and made interesting observations on the fructification. 



FrucJificatio7i. This may arise either from the roots, 

 often at some distance from the trunk, or on the trunk 

 itself up to 10 or 12 ft. When growing on roots that are 

 buried its connexion with the tree may not be observed until 

 the roots are bared of earth, but in other cases it may arise 

 from parts of roots that are exposed to the surface. In 

 either case it is stipitate, i.e. has a stalk with an expanded 

 pileus as in fig. 46. Sometimes, as in the figure, two or more 

 stalks may grow up side by side and their respective pilei 

 grow into each other, or become congruent. The pores are 

 borne on the lower side of the pileus, and the uj)per swollen 

 part of the stipe also becomes pore-bearing, so that there 

 is no sharp line of demarcation between the pileus and the 

 stipe. When growing on the trunk the fructification has 

 a. totally different form. It is then bracket-shaped, as in 

 fig. 47, with a more or less distinct stalk ; and often the 

 brackets are imbricated, borne closely one above another, 

 in which case there is usually no stalk visible. The fruit- 

 bodies are generally about G in. across, but specimens up to 

 16 in. have been measured. 



Though the two forms of fi'uctification are so different 

 in their general shape, the details of structure are identical. 

 The upper surface is dark, reddish brown in colour, and 

 rough with excrescences. The pore-bearing under-surface 

 is greenish when young, but changes to red on being touched, 

 and during the period of active growth it exudes numerous 

 drops of liquid. I^nhke Fomes annosus, the fructification 

 is not woody, but soft and fairly light. It hardens some- 

 what with age and dries up and dies in the autumn. It 

 generally falls from tfie tree in late winter unless it has been 



