W. J. Dowsoit. 
’a i i 
solution. All the dead and the greater part of the discoloured 
tissues were found to contain hyphae which were most abundant a 
short distance behind the junction of discoloured and healthy tissue. 
Behind this area the hyphae appeared to retreat from the wood to 
the cortical tissues for purposes of reproduction. The amount of 
gum in the tissues that had been dead some time was less than in 
those which were situated at the line of demarcation between 
healthy and unhealthy tissues. It would appear that gumming 
proceeds a little in advance of the hyphae, a phenomenon also 
observed by Brooks 1 in Plum trees attacked by Stereum purpureum. 
This is in accordance with the well-known fact that Plum trees 
produce quantities of gum upon injury. 
The amount of gum produced was so great in some junction 
areas which took the form of a fairly flat and oblique plate and not 
a central elongated cone, that in longitudinal sections the gum 
floated out as long (2—3 mm.) ribbonds and cylinders. The vessels 
in these areas were completely blocked by the long plugs of gum. 
The presence of the parasite no doubt causes the gumming in the 
vessels and tracheids ; but it is the actual gum which kills the 
branch by stopping the transpiration current. The mycelium is to 
he found in all the elements of the wood, but especially in the 
vessels and medullary cells; it also occurs in the pith and cortex. 
In those cases where a diseased central cylinder is present the 
mycelium appears to travel rapidly up the pith in a similar manner 
as described by Brooks and Bartlett 2 in the case of Botrytis attacking 
Gooseberry bushes. The hyphae pass in a horizontal direction 
into neighbouring tracheids and vessels through the simple or 
slightly bordered pits, and also in the medullary ray cells in like 
manner (Pig. 3, E, F); but do not bore through the walls, which 
are not delignified. 
A curious feature of the mycelium was noticed in those diseased 
areas where the hyphae were most abundant. Some of the hyphae 
had broken up into a number of small oval-shaped bodies which 
were present in great numbers. In the cutting of the sections 
masses of these oval bodies were scattered up and down the vessels 
by the action of the razor and subsequent treatment. So far I 
have been unable to discover what function these bodies perform, but 
would suggest that they are the result of the disintegration of the 
hyphas, owing to the age or lack of nourishment, or both (Fig. 3, G). 
1 “Silver Leaf Disease.” Journ. Agric. Soc., 1911-1912. 
* “ Two Diseases of Gooseberry Bushes.” Annales Mycologici, vol. 8, 
No. 2, 1910. 
