HEART-ROT 113 
and in these it was found that the hyphac had penetrated to 
the stem. 
" Thus question 1 can be answered in the negative, ques- 
tions 2, 3, and 4in the affirmative. Infection does not take 
place through unwounded roots, at any rate under the 
circumstances of the experiments (too much confidence 
must not be placed in a negative result), but can take place 
through a living wounded root or through a dead root. 
Mode of attack in nature. The habit of the fungus leaves 
no doubt as to the part of the tree which is first attacked. 
It is always the roots which first become infected, and in 
every case that has been recorded the disease has spread 
from the roots to the stem, and not vice versa. Infection 
then, must be subterranean, or immediately on the surface 
of the soil. 
Hartig (1878), who at that time was unaware of the 
existence of conidia, recognized two possible means of 
infection. One was by the spores of the fungus reaching 
the roots of healthy trees, and the other by living roots 
coming into contact with roots which contained the fungus. 
These two methods will be discussed in turn, and as they 
do not seem adequate to account for all the infections which 
occur in nature, a third method will be suggested. 
(i) Infection by means of spores. The fructifications of 
the fungus are usually subterranean, or if they grow above 
ground they bear their spores so near to the soil that wind 
can play but a small part in the dispersal of the spores. 
Often fructifications which begin to. develop subaerially 
become covered by fallen leaves and shoots of ivy, but this 
seems rather to encourage than retard their development. 
Thus it is presumed that spores are carried by other means 
than air currents, and, as Hartig suggested, rabbits, voles, 
and other burrowing animals are probably the chief agency 
in dispersal. The fructifications require some open space 
for development, and burrows, made by animals under the 
trees, afford the kind of station in which they flourish. So 
there is reason to think that such animals catch the spores 
‘in their fur or pick them up on their feet, and they may 
1888 ig I 
