26 THE LARCH CANKER 



from placing spores in contact with the mucilaginous 

 excreta of the Chermes in the spring. 



A. P. Anderson (1902) gave an account of canker on 

 Abies balsamea, which is caused by an allied species, Dasy- 

 scyplia resinaria. This canker resembles, in most respects, 

 that of the larch, and the further details which he provides, 

 especially in connexion with resin flow, are for the most 

 part equally true for the larch canker. 



Munch (1909) carried out some interesting experiments 

 on the relation between the rate of growth of a canker and 

 (i) the air-content of the tissues, (ii) the temperature. He 

 cut young shoots (5 cm. broad), which, though cankered, 

 were still living, into strips 20-30 cm. long, each with 

 a canker. These he dried to varying extents, and found 

 that the canker spread much more rapidly in the drier than 

 the moister stems. He attributes this to greater air-content, 

 but it may also be accounted for by the lessened vitality 

 of the tissues induced by drying. He also found that the 

 minimum temperature for the growth of the fungus is 

 above C., so that it must be incapable of spreading during 

 an Alpine winter. jtx< 



The mycelium of Dasyscypha calyeina in the larch stem 

 and its effect on the tissues. The hyphae of D yscyp/iu 

 calyeina have been found in the outer cortex of the leaf 

 cushions, the inner cortex, the phloem and xylem, and the 

 medullary ray portions of the cambium. 



Its presence in the leaf cushions of uninjured larch stems 

 is of no practical importance. No great development of 

 Dasyscypha hyphae has been observed in this region ; but 

 that there is sufficient nutriment for fungal sustenance in 

 these cushions, even when they have been cut off by a cork 

 layer, is demonstrated by the fact that fungal pycnidia may 

 not infrequently be found growing in them. If the hyphae 

 of Dasyscyp/ia obtained a firm hold on the cushion, any 

 weak points in the cork armour would be liable to discovery, 

 which would put the plant in danger of infection without 

 previous wounding ; but there is no direct evidence for this 

 ever having taken place. 



