96 DISEASES OF TREES 



Very frequently N. ditissima is found associated with Aphides^ 

 Lachnus exsiccator produces large galls in the cambium of the 

 beech, and when these afterwards burst open they present the 

 opportunity of infection to the fungus. The mycelium spreads 

 in the cellular tissues with extraordinary rapidity. The beech 

 Aphis, too, Chermes fagi, which clothes the stem with a white 

 woolly covering, is often associated with the fungus, which, under 

 these circumstances, quickly kills the cortex, without producing 

 canker-spots. 



NECTRIA CINNABARINA. 2 * 



This Nectria is certainly one of the most widely distributed 

 of fungi, and finds its way on to almost all dicotyledonous trees 

 and shrubs when they have been killed by frost. Besides living 

 saprophytically, it also occurs as a parasite, and that most fre- 

 quently on the maple, lime, and horse-chestnut. Infection usually 

 occurs at branch-wounds, though also very frequently at root- 

 wounds, which cannot be avoided when transplanting either large 

 or small trees. The mycelium of this fungus, which grows rapidly 

 upwards in the vessels, penetrates into all the elements of the 

 wood, decomposing the starch, and leaving a green substance be- 

 hind, Fig. 45. The consequence is that the wood turns black, 

 while the cambium and cortical tissues remain sound. The wood 

 becomes unable to conduct sap, the leaves wither prematurely in 

 summer or dr&p off, and the cortex of the youngest shoots 

 dries up after the wood is completely dead. In autumn or the 

 following spring the cinnabar-coloured stromata that bear the 

 gonidia appear grouped together in large numbers on the dead 

 cortex. On account of their size and colour they are conspicu- 

 ous even from a distance. The large rough perithecia which are 

 formed later are much darker red in colour. 



It is interesting to note that this fungus cannot injure the 



1 Untersuchungen aus dem Forstb. Inst. zu Miinchen, I. pp. 151 163. 



2 . H. Mayer, Ueber den Parasitismus von Nectria cinnabarina. Un- 

 tersuch. a, d. Forstb. Institut zu Munchen, III. 



* [This fungus is extremely common on black currant and other trees in 

 England. It is the species which, in its gonidial form, is so often observed 

 on pea and bean sticks, dotting them over with scarlet points. ED.] 



