A NKW APPLE TREK CANKER. 267 



the pure cultures grown from the pycnospores. The inoculum 

 was introduced into a wound in the stem made with a steriUscd 

 scalpel, and the wound covered with moist filter paper. By the 

 1 2th of the month black areas surroundins: the wounds were 

 clearly visible. As controls, a similar wovmd was made in one. 

 but no mycelium introduced, and in another, mycelium of a 

 fungus which had also been isolated was introduced, both being 

 covered with moist filter paper. In both of the controls the 

 wounds healed up- (Plate XXVII a. c.) 



By June the black areas in one had develo])ed into a sunken 

 canker, i^ cm. wide by 6 cm. long, this being cut off from the 

 healthy tissue by a brown corky fissure. A number of smaller 

 pustular bodies were present on the surface which had not yet 

 ruptured the outer layers of the periderm ; these on sectioning 

 proved to be stromata. containing what appeared to be immature 

 fruiting bodies. The wood was discoloured, under the cankered 

 area for about a distance of 4 mm. (Plate XXVII c. ) The coluur 

 was a yellowish-brown, which after several days turned almost 

 black. This possibly accounts for the blackening of the wood 

 in many of the trees in the orchard after the cankered bark had 

 been removed. In a young canker about three weeks old, which 

 was obtained by inoculating a twig about 3^ cm. in diameter, the 

 blackened dead tissue was surrounded by a narrow water-soaked 

 zone, about i mm. wide, this grading externally into healthy 

 tissue. A section of the wood, stained in Delafield's haematoxylin 

 and eosin accordnig to the method if Durand (12), showed a 

 delicate mycelium in the outer layers. Discoloration of the wood 

 extended, after about seven months, some three to four inches 

 up the stem in the case of one of the inoculated apple stocks. 

 (Plate XXVIIIa.) 



The fungus was re-isolated from the larger canker as follows : 

 — A fine shaving was cut oft with a sterilised razor from a piece 

 of the blackened bark, just removing the outer periderm ; the 

 razor was sterilised again and pieces of tissue containing the 

 stromata cut out and inserted into prune agar slant tubes and 

 incubated at 31° C. After about 48 hours typical white cottony 

 growth was apparent in each. Not every cne of the later in- 

 oculations with the original strain took effect. It may be that 

 the pathogenic power of the fungus wanes when grown for any 

 length of time on artificial media ; or possiblv the incisions made 

 in the bark were allowed to dry out too rapidly ; or perhaj)s the 

 resisting powers of the tree may differ at different times of 

 the year. 



Inoculation of fruits. — Inoculations of sound fruits by 

 making an incision into the skin with steriUsed scalpel and 

 inserting by means of platinum loop a suspension of spores 

 obtained from pure culture resulted, after about 10 days, in a 

 yellow sunken area. Later concentric zones of black fruiting 

 bodies were formed. (Plate XXVIII/^) 



