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317 
Two days later the upper portion of the tree beginning from the 
Botrytis zone was in a desiccated state, and the leaves were 
brittle and easily detachable. These symptoms are significant 
of a very recent cause of drought due to a factor operating in so 
active and rapid a manner as to form almost immediately a com- 
plete barrier to all water conduction in the stem. If the Botrytis 
mycelium in the diseased region is this factor, as appears to be 
the only probable hypothesis, iis behaviour is remarkable. 
period averaging 20°29 C. and the minimum 6-7° C. From 
May 16th until May 23rd the weather was dull and showery, 4°19 
ems. of rain falling in seven days. The average maximum tem- 
perature fell by three degrees, whilst the average minimum 
increased by three. From May 24th until the end of the month 
ere was a recurrence of the earlier weather conditions with a 
slightly increased temperature but occasional dull days. Rain 
only fell on the 29th May when 1 cm. was recorded. 
It is well known that the active development of Botrytis is 
peculiarly dependent upon the presence of warm, humid, and 
equable conditions. and this is’ especially true of the infection 
stages. The brief wilting period indicating the unusual rapidity 
with which the fungus must have developed in the tissues has 
already been noted. When these factors are borne in mind, and 
the various phenomena presented by the host tree are correlated 
_ with the weather conditions, it appears extremely probable that 
the primary fungal attack must have occurred during the du 
wet week of equable temperature extending from May 16th to 
May 23rd. This would give a maximum period of fifteen days 
from the initial penetration of the mycelium or germinating 
Spore to a state of host permeation resulting in the complete 
desiccation of the tree. 
General Distribution of the Fungus in the Host.—In order 
to determine the degree of penetration of the host tissues by the 
fungus, the main stem of the tree was carefully divided in a 
radial longitudinal plane. The diseased area was then visible 
by reason of its discoloration, and this was greatly accentuated 
by a few hours’ immersion in water (Pl. vii. Fig. 3). 
In section the diameter of the’ affected portion of the stem was 
appreciably less than that of the non-affected regions, but the 
most striking distinction lay in the general appearance and 
