H. WuRMALD \i)') 



The investigation is still in progress but it was thought desirable 

 that the facts already ascertained should be published in order that 

 steps might he taken to check the further spread of the disease. 



III. The Disease as observed on naturally infected trees. 



{(i) Ohservations made in 1915. 



An opportunity for studying the disease under conditions favourable 

 for close examination occurred in 1915 when a row of apple trees in the 

 fruit plantation at Wye College was found to be attacked by the Blossom 

 Wilt. The trees, forty-eight in number, were of the varieties Warner's 

 King and Duchess' Favourite planted alternately and were "closely 

 spur-pruned" bush trees about eight feet high. Detailed observation 

 commenced early in June 1915 and the following facts were noticed : 



Not one of the trees was entirely free from Blossom Wilt though two 

 of them had but one dead truss each, while the tree which had suffered 

 most had 1.32 wilted trusses of blossom or about one-third of the total 

 number present. The affected trusses (inflorescences) were recognised 

 by their brown and withered drooping flowers and leaves; they were 

 often greyish since the edges of the withered leaves showed a tendency 

 to curl inward thus exposing the hairy under surface of the leaves. 

 That some disintegration of the tissues had occurred was evidenced by 

 taking a spur between the thumb and finger, immediately below the 

 insertion of the inflorescence, when it was found that, when pressure was 

 applied, the diseased spurs were more easily compressed than was the 

 case with healthy spurs, and wilted trusses were easily broken off at the 

 lower limit of the vear's growth. The short axis of the inflorescence 

 was at this time quite dead and when cut across was brown throughout; 

 microscopic examination showed the presence of mycelium in the cortex, 

 xylem and pith, the last sometimes being almost replaced by interwoven 

 hyphae. The discoloration of the tissues extended to the older parts of 

 the spur particularly in the cortical region and frequently reached the 

 branch bearing the spur. 



Some of these trusses, shortly after wilting, produced Monilia 

 pustules on the dead flowers during a period of wet weather but in the 

 majority the mycelium within the tissues apparently remained sterile 

 throughout the summer. When however some of the latter were broken 

 off from their spurs (i.e. at the lower limit of that year's growth) and 

 placed on damp filter paper in a large petii dish, pustules of conidia 

 readilv appeared on the exposed broken end and on the withered flowers ; 



