74 THE LARCH CANKER 



thus i)i()cliKijig ail iiini)liitheatrc-likc appeaiaiice in the 

 wood of a transverse section. The mycehnm flourishes 

 chiefly in the cortex and the phloem, but can also attack the 

 wood to a limited extent. 



It has been shown that this fungus is not a parasit<5 in 

 the sense in wliich the term is generally used. • The myceliinn 

 does not directly attack the living cells of the host, but first 

 kills tliein by secretions. The mycelium grows both in the 

 cells of the host and in the intercellular spaces. Fructifica- 

 tions are borne on the dead bark in the canker region. These 

 arc larger than those on the dead branches in all their pai'ts, 

 but it has been shown that this difference is due to growth 

 conditions, and the dimensional differences cannot be 

 made the basis of sjjecific or varietal separation. 



Large quantities of resin are made by all attacked parts 

 of the tree. This oozes out on to the surface of the canker, 

 and often forms long streams down the trunk. 



Pure cultures of the fungus have been grown on various 

 media, including sterilized twigs of different conifers and 

 dead needles of larcli, spruce, and Scots pine. Fn a damj) 

 chamber larch needles may become matted together by the 

 mycelium whicli ramifies the mesoj)hyll. It is suggested 

 that the matting of needles on the floor of larch plantations 

 may be largely due to the mycelium of this fungus, a process 

 which may help in the decomposition of the foliar debris. 

 Pure cultures on sterilized larch stems were grown up to 

 the stage of bearing apothecia, thus comj)leting the cycle 

 from spore to spore. 



The fungus may gain admission to the living parts of the 

 tree in three ways : 



1. Through wounds, which may be caused by a variety 



of agents. 



2. By growing down fiojii the dead branches into the 



living tissues of the trunk. 

 .'{. By means of ])uds wliich have been killed by the 

 shading of the upper Ixanches. 



It has been shown that the second of these methods gives 



