32 



THE LARCH CANKER 



found a similar formation of resin dncts 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 



Fio. 11. — Radial longitiulinal section of abnormal wood: a, snmmpr 

 wood of previous year, almoi'inal — ono cell sliows tertiary lliickoning; 

 h, sliort sclcrenchyn^'i'tous elements ; c, long sclcrenchymatous elements ; 

 d, nearly normal xylem. 



except in its crown. Wo have rather to look for the cause 

 in the reduction of food supply which may be brought about, 

 cither by defoliation, or by the death of i\\v phlo(Mu in the 

 neighbourhood of the developing wood. 



In the canker the formation of normal wood is resumed 

 onlj^ when new ])]il()(Mn has been made outside, which forms 



