20-2 A Wnssonf Wilf and Caidrr of Apph' Trees 



killed and conidia placed in hanging drops germinated readily. It 

 would seem however that the surface layers were killed and the ([uestion 

 is whether this would be sufficient to prevent the fall of the conidia 

 during the critical period when the flowers are open if the spraying 

 were done as late as possible but before the flowers expanded. It is 

 proposed to carry out ex])eriments in the open to test this point. 



In conclusion I desire to thank Prof. L. R. Jones (Wisconsin), 

 Ur U. B. Posey (Oregon), Mr McCubbin, M.A. (Ontario), and I)r Quanjer 

 (Holland), who have kindly sent specimens of mummified fruit or 

 cultures from abroad, also Dr Pethybridge and Mr J. M. Hector, B.Sc, 

 who sent mummified fruit and diseased branches. I am indebted also 

 to Mr Salmon (head of the Mycological Department at Wye College) 

 whose advice and criticisms throughout the investigation have been 

 invaluable. 



Summary. 



1. A. "Blossom Wilt and Canker" of apple trees, produced by a 

 species of Monilia, is causing great loss to fruit growers in the south- 

 east of England. 



2. Infection takes place through the open flowers; the fungus 

 invades the tissues of the flowering spur, thus killing the inflorescence 

 and the leaves of the spur; the disease may reach the branch and 

 produce a canker. 



'3. Spurs killed during the summer, together with the accompanying 

 cankers, produce pustules of conidia during the following winter and 

 spring; these conidia, falling on the flowers as they open, give rise to a 

 new outbreak of the blossom-wilt disease. 



4. When a canker has shed its crop of conidia it becomes covered 

 with callus which eventually heals the lesion. 



5. Inoculation of apple flowers with conidia from pure cultures of 

 the fungus resulted in the death of the inflorescences and the spurs ; 

 in some cases cankers were produced. Conidia-bearing pustules of the 

 organism appeared on these dead spurs and cankers during the following 

 winter. 



6. The causal organism is a grey Monilia easily distinguished from 

 M. fructigena; at present it is to be referred to Monilia cinerea Bon. 



7. On culture media the habit of the fungus is different from that 

 of the grey Monilia (also leferred to M. cinerea by American workers) 

 which is commonlv found in North America. 



