32 THE LARCH CANKER 
found a similar formation of resin ducts in larch which has 
been attacked by the sawfly. These comparisons do not 
support the contention of de Vries (1876) that such wood 
is the result of reduced tangential pressure produced by 
a wound, since in two cases the tree was not wounded 
a ee 
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Tic. 11.—Radial Jongitudinal section of abnormal wood: a, summer 
wood of previous year, abnormal—one cell shows tertiary thickening ; 
b, short sclerenchymatous elements ; c, long sclerenchymatous elements ; 
d, nearly normal xylem. 
except in its crown. We have rather to look for the cause 
in the reduction of food supply which may be brought about, 
either by defoliation, or by the death of the phloem in the 
neighbourhood of the developing wood. 
In the canker the formation of normal wood is resumed 
only when new phloem has been made outside, which forms 
