112 HEART-ROT 
4, Can trees be infected through growing on infected 
soil ? 
In order to infect the trees they were lifted from the 
ground and their roots were washed in running water. 
Pieces of infected roots, or lumps of infected soil, taken 
from pure cultures were tied to roots of the trees by means 
of bast. Infection points were tied round with sterilized 
moss, and the trees were carefully potted in suitable soil. 
On March 30, 1915, twenty-four infections were made with- 
out wounding, eighteen with slight scalpel wounds into the 
phloem, eighteen on roots still attached to the trees which 
had been placed in nearly boiling water for one minute in 
order to kill them, whilst the other roots of the trees remained 
alive, and twelve on roots which were both boiled and 
wounded. 
None of the infections were effective where there was no 
wound, whereas all those where the fungus had touched 
a wound were successful. In these successful infections the 
mycelium grew into the wood and usually reached the 
centre of the root. The hyphae grew both upwards and 
downwards in the wood and bark, killing and browning the 
tissues on their way. Growth was very slow, but rather 
more rapid in the wood than in the phloem, where it was 
always hindered by cork layers which were made across the 
phloem and cortex as an obstruction. The extreme slowness 
of growth is shown by the fact that in most cases the 
mycelium had only spread 5-6 mm. upwards and downwards 
in the wood and about 1 mm. less in the phloem in six months. 
Infections on killed roots were invariably successful. In 
five weeks the mycelium had spread to one and a half inches 
in the wood, and since infections were mostly made on the 
larger roots the hyphae soon spread to the stem and killed 
the tree. With some of the trees, whose experimental roots 
had been killed, I was doubtful whether enough healthy 
roots had been left to supply water during the summer 
months. On this account I cannot be certain that death 
was always brought about by the fungus. But some were 
examined as soon as the trees began to look unhealthy, 
