24 Transactions British Mycological Society. 
and to become completely dried up: in all about fifty branches 
were kept under close observation from the time wilting was 
first observed, and in every case the branch which had lost its 
leaves became covered with the pink stromata of Nectria during 
the following winter. 
A number of similar branches were removed from the bushes 
as soon as the wilting was observed. When cut open it was 
found that a brownish green region was present in the wood at 
the base, extending almost across the branch, leaving a small 
area of white and healthy wood, with a corresponding area of 
healthy cortex external to it. 
This discoloured portion could always be traced either to a 
wound in the branch itself or more commonly to a dead side 
branch; in many cases these dead portions already bore stromata 
of Nectria. 
The discoloured portions of wood and cortex were found to 
be full of fungus mycelium extending up to the edge of the 
white and healthy wood, the vessels and tracheids being choked 
up in the darker parts with hyphae and gummy material. This 
characteristic discoloration of the wood was observed by Mayr 
in the wood of Norway maple, and he considered the gummy 
liquid represented the product of solution of part of the cell 
wall by the fungus. Fig. 3 shows the hyphae in the wood cells 
taken from the edge of the discoloured zone; it is seen that in 
the early stages of invasion the fungus appears incapable of 
invading the living ray cells; later on these also become filled 
with hyphae. It was never found that the fungus advanced in 
the cortex before the wood was blocked up, in fact there seemed 
no evidence that it could effect an entrance into any living cell 
in a normal healthy condition. 
EXPERIMENTAL WORK. 
A. In the laboratory. 
Twelve typical branches were selected with discoloured por- 
tions attached to them, but no visible stromata or signs of the 
presence of any fungus upon them; after thorough scrubbing 
they were placed under sterile conditions in jars of water under 
bell jars. In six weeks every branch began to show the pink 
stromata of Nectria breaking through the bark, commencing 
round the discoloured regions. (Control branches developed a 
little Cladosporium under these conditions.) 
Portions of the wood from different parts of the discoloured 
regions were removed from another batch of branches under 
sterile conditions and were transferred to Petri dishes of sterile 
agar jelly. 
