THE LARCH CANKER 31 
them. The hyphal development in the wood never seems 
to be of a nature that can cause reinfection of the phloem, 
so that probably the hyphae get round the cork layer in 
the cambium just outside the wood, and spread from that 
point. Cork formed in the vicinity of the fungus is apt to 
become red. This is due to infiltration with resin, and cork 
cut fresh from a healthy tree may be made to assume this 
red colour by boiling in resin. 
(iii) The character of the secondary wood which is made 
in the neighbourhood of the canker is also profoundly 
affected. 
Where the cambium is killed, of course no more wood 
can be formed ; but the cambium which is still living on the 
flanks of this dead patch cuts off wood elements which are 
essentially different from normal xylem (fig. 4 and fig. 11). 
The cells which are first differentiated in the spring wood 
remain thin walled and show no tendency towards sliding 
growth. Their walls become lignified and have numerous 
simple pits. Sometimes the living contents remain, but not 
infrequently they become disorganized and are replaced by 
water. Thus in many ways they resemble medullary ray 
parenchyma, except that they are extended longitudinally 
instead of radially. Irregular intercellular spaces are formed 
between them, and these often become filled with resin. 
Normal resin ducts are also formed, besides such irregular 
abnormal ones (fig. 4, p. 8). 
As the summer advances tracheides are formed. These, 
however, have an irregular wavy outline, which gives 
a truly longitudinal section the appearance of being oblique, 
although entire tracheides may be included in it. Subse- 
quently formed tracheides are normal except. for the fre- 
quency of a tertiary spiral thickening of the walls. Tannin 
cells are frequent throughout this portion. 
The significance of this abnormal wood is difficult to 
define. In many respects it resembles the wound-wood 
described by VOchting (1892) and Kuster (1903); but 
Hartig (1892) figures a very similar development in spruce 
after defoliation by the nun moth, and Harper (1913) has 
