94 



DISEASES OF TREES 



almost complete decomposition of the tissues of the cortex, with 

 the exception of the outer periderm layers. Only on those 

 parts of the cortex which have been killed during the past year 

 that is to say, on the periphery of the 

 canker-spot do white gonidia-bearing stro- 

 mata appear. These had already been ob- 

 served by Willkomm in his investigations 

 into the canker of the beech, by whom they 

 were designated Fusidium candidum. On these 

 the minute deep-red perithecia originate, but 

 they can only be discovered after careful 

 search. They are found partly in groups and 

 partly singly on the dead cortex, and especially 

 in the fine fissures, Fig. 40. One sometimes 

 searches for them for a long time in vain upon 

 the older canker-spots, for the reason that 

 these have ceased to increase in size at all parts 

 of their circumference. In Fig. 43 the canker- 

 spot is increasing in size only in the upper 

 left-hand corner, and it is only there that the 

 red perithecia are to be found in abundance. 



In the case of the canker of the beech, I 

 have frequently observed that sooner or later 

 the mycelium ceases to advance at certain 

 places, in consequence of which the shape of 

 the canker-spots becomes exceedingly irregu- 

 lar. Here and there the canker spreads for a 

 series of years, but finally the diseased spots 

 may be entirely covered over by a kind of 

 callus. See Figs. 43 and 44. 



It may also be remarked that the parasite 

 is distributed throughout the whole of Ger- 

 many, and that canker of the beech especially 

 is met with from the Island of Riigen to the 

 south of Bavaria, being very prevalent, for 

 instance, in the neighbourhood of Munich. 

 Young trees from five to ten years old, as well as trees 140 years 

 of age, may be attacked by the disease, which, however, in the 

 latter case, is confined to the twigs and branches of the crown. 



FIG. 42. Branch of 

 a beech showing 

 numerous canker- 

 spots, which do 

 not appear to have 

 been preceded by 

 any cortex wounds. 



