^CHAPTER VI 

 HEART-ROT. FOMES ANNOSUS (Concluded) 



Reproductive organs : fructifications ; conidiophores. Pure cultures 

 on artificial media. Cultures on natural media. Infection experiments. 

 Mode of attack in nature. The frequency of heart-rot in plantations 

 which form the first rotation on cultivated soil. Methods of prevention. 



Reproductive organs. Fomes annosus has two kinds of 

 reproductive organs. These are (1) fructifications, usually 

 large, of Polyporus form, which may occasionally be found 

 associated with larch heart-rot, but which are much com- 

 moner on young trees of other coniferous species when 

 they have been killed by the fungus ; and (2) conidia on 

 somewhat specialized conidiophores, which occur regularly 

 in all cultures, but have been found, so far, only very rarely 

 in a truly wild state. They are apparently formed only in 

 a saturated atmosphere, such as is provided under usual 

 cultural conditions, but which cannot be relied upon in 

 nature. 



The morphology and life-history of the fungus have been 

 carefully worked out by Brefcld (1889) under the name of 

 Heterobasidion annosum, (Fries) Brefeld, and I have made 

 free use of his description in the following account. 



1. Typical fructifications are shown in figs. 29, 30, 39, 40. 

 They are of two kinds bracket-shaped, borne usually on 

 the sides of trunks and above ground, and ' resupinate ', 

 which grow on the under -sides of roots and have the whole 

 or nearly the whole of the upper side attached to the root. 

 The latter form is generally subterranean, and has its lower, 

 spore-bearing side exposed in some hole in the ground, 

 such as those made by rabbits and mice. 



The fructifications first arise as small white masses of 

 hyphae, often no bigger than a pin's head. These break 

 through the bark of the roots and broaden on the surface 



