1G8 A Blossom Wilt and Canher of Aj^ple Trees 



a general resemblance to the Monilia cankers that it seemed probable 

 that they had been caused by the fungus, whose further development 

 had been arrested. The condition of such cankers together with 

 observations made subsequently on younger cankers suggested that 

 the fungus did not survive after it had produced its crop of conidia. 

 Tn support of this it was found that the formation of callus had already 

 commenced beneath the bark of cankers still bearing the pustules of 

 the fungus (Fig. 8). 



The observations made in June 1915 and recorded above suggested 

 the following hypotheses : 



(1) Infection arises from conidia falling upon the open flowers, 



(2) The conidia are produced on spurs killed during the previous 

 flowering season and on cankers arising round the base of the dead 

 spurs. 



(3) When the fungus has produced its crop of conidia on a spur or 

 canker its further development ceases and in the case of cankers the 

 injured surface becomes healed over by a growth of callus. 



That the fungus was a true parasite and able to produce both the 

 Blossom Wilt and Cankers was definitely proved in 1916 by means of 

 inoculation experiments with pure cultures as is shown later in this 

 paper. The other two points were established by attaching numbered 

 labels to affected spurs and cankers, and recording observations at 

 certain periods. After a few weeks this revealed another interesting 

 feature relative to the cankers. It was found that not only did the 

 older cankers (i.e. those produced in the previous year) show no further 

 extension of the injury produced, but that the newly formed cankers 

 also ceased to increase in size ([uite early in the season ; many of them 

 had attained to their maximum size by the middle of June while in 

 others a slight increase in the cankered area could be detected towards 

 the end of June or early in July, but in no case did a canker show any 

 extension after July 12. It would appear therefore that the fungus 

 penetrates no further into the tissues of the host after some six or eight 

 weeks from the inception of the disease. 



{})) Observations made in 1916. 



The observations were continued in 1916, those spurs and cankers 

 labelled in 1915 being examined from time to time while other cankers 

 produced duiing May and June 1916 were also labelled; in all a record 

 was kept of over 100 spurs and cankers and in no case was there any 

 evidence that the fungus was able to make anv further advance into 



I 



