CHAPTER II 

 THE LARCH CANKER 



General. Historical. The mycelium of DasyscypJia calycina and its 

 effect on the tissues. The canker as a pathological structure. 



General. The canker or blister of the larch is by far the 

 best known of the diseases of this tree. It is exceedingly 

 common and very destructive, and, since none of the methods 

 which have been adopted with a view to preventing attack 

 have met with success, the pest bids fair to become even 

 more disastrous in the future than it has been in the past. 

 In Germany it has already made larch growing so un- 

 profitable that the tree has almost ceased to be planted 

 except where sparingly mixed with other species, and a like 

 fate must follow it in many parts of Britain unless a system 

 of growing can be adopted which will to some extent obviate 

 the evil. 



The disease is due to a fungus which has been called by 

 a variety of names, but is now generally known as DasyscypJia 

 calycina* in Britain and D. Willkommii on the Continent. 

 This fungus belongs to the class Ascomycetes, since it bears 

 its spores in eights inside an enlarged hypha or ascus 

 (fig. 18, A, p. 40), and it is placed in the sub-class Dis- 

 comycetes since its fructification is in the form of an open 

 cup or apothecium (fig. 17, p. 38), which is lined on the 

 upper concave side by the asci arranged at right angles to 

 the surface. 



D. calycina is almost universal on recently dead branches 

 of larch trees. Its fructifications are very small, being 

 seldom more than one-eighth of an inch in diameter, of bright 

 orange or yellow colour above and white below, and each 



1 The synonymy of Dasyacypha calycina is discussed in a note at tin* 

 end of Chapter IV. 



