A NKW Al'PLI': TKKK CANKICK. 259 



besides spraying the trees regularly as a preventive with lime- 

 snlphur. P(issibly one reason why the disease has made head- 

 way in the orehard, notwithstanding the pains taken to control it, 

 is that the fungus is present in the outer layers of the wood ; 

 failure to cut this diseased wood out when removing the canker 

 would, of course, seriously detract from the value of the opera- 

 tion. I think, too, that woolly Aphis has be-^n instrumental in 

 spreading the disease. 



As far as rot of the fruit is concerned, Mr. Bratidmuller 

 has not noticed am- difference between the fruit from diseased 

 trees and fruit from healthy ones. 



Examination of one of the branches (Versfeld) showed 

 the presence of numerous pycnidia, these being visible externally 

 as minute black spots. Cultures were plated out from the spores, 

 vrhich were present in abundance, and at the same time the 

 germinating power of the spores was tested. It was found that 

 they germinated readily in nutrient solutions and in distilled 

 water. The fungus was found to grow readily on nutrient media, 

 so that the isolation of pure cultures was easily effected. In- 

 oculations of the mycelium into two young Northern Spy stocks 

 caused the develo])ment of black sunken cankers on both, while 

 the wound made in a control tree similarly treated, except for 

 the introduction of fungous mycelium, healed perfectly well. A 

 characteristic of the cultures was the evident unwillingness of 

 the fungus to form spores or fruiting bodies. I shall return to 

 this point later on. Owing to this, and also to press of work, 

 the investigation was laid aside for about two months, when I 

 again made an examination of the original material. Sections of 

 pieces of the bark which had been fixed in boilmg lO per cent, 

 formalin and cut on a freezing microtome showed that amongst 

 the pycnidia there were bodies of similar shape but containing 

 what appeared in some cases to be immature asci, in others a 

 compact mass of delicate interwoven hyphse. Pieces of the bark 

 were then placed in a moist chamber and examined after 24 and 

 48 hours. It was found that, firstly, the pycnidia exuded out 

 from the stromata, and could be seen as whitish specks on the 

 surface, and. secondly, that the supposition of the presence of an 

 ascus stage was correct, asci containing ascospores being fairly 

 frequent. Plate XXVII (b) shows a portion of a cankered 

 limb of \'ersfeld apple; the view^ on the left of the photograph 

 shows the discoloration of the wood due to the growth of the 

 fungus. 



Description and Sy.stematic Position of the Fungus. 



Hesler (i), who proved the perfect stage of Spharopsis 

 maloriim Berk to be Physalospora cydoiiicc, notes that there is 

 some variability as regards the colour of the pycnospores in this 

 fungus, which ranges from dark to hyaline ; the latter may 

 frequently be quite capable of germination, in which case he 

 considers them to be prematurely ripe. He also notes that the 



