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 Brefeld (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 
