550 DIE-BACK OF APPLE TREES. 



These cells evidently belong to the hyphal tissue already referred 

 to from and in which the pycnidia are formed. 



Control. 



It is doubtful whether spraying already diseased trees with 

 any of the ordinary fungicides will be accompanied by beneficial 

 results, except in so far that it will prevent the further spread 

 of the disease. The only method of effectually combating the 

 disease appears to be the removal and burning of the affected 

 parts. 



When only the branches are diseased, these should be well 

 pruned back and immediately burned. Where the malady affects 

 the base of the tree, it is best to uproot and destroy the diseased 

 tree as soon as possible, and thus prevent further infection. 

 Cankers on limbs, etc, should be removed ; the woiuid painted 

 over with some disinfectant, and the formation of the fruiting 

 bodies of the fungus guarded against. Winter applications of 

 lime-sulphur, Bordeaux mixture or coj^jjer sul])hate, i lb. in 25 

 gallons of water, will reduce the number of twig infections. 



Isolation and Growth of the Fungus. 

 A. Isolation. 



The fungus herein described was isolated from apple 

 branches (Herb. No. 3831), submitted by Mr. Petty, Swinburne, 

 Orange Free State. It is interesting in this connection to know 

 that in the year 1912 Mr. Petty submitted specimens of apricot 

 and plum attacked by Cytospora leiicostoiiia ( Pers. ) .Sacc. 



On the 7th August, 19 14, a portion of the apple twig bear- 

 ing p}cnidia was sterilised in Mercuric chloride ( i :iooo), 

 washed in distilled water, and some of the pycnidia removed 

 with a sterilised knife and crushed on a slide in sterilised dis- 

 tilled water. From this some melted beefbroth agar tubes were 

 inoculated and incubated at 25° C. On the nth August, 1914, 

 a ricli mycelial growth had developed in one of tlie tubes, and 

 from this were poured beefbroth agar and oatmeal agar plates. 

 By the 20th a blackish growth had formed in the oatmeal-agar 

 plates, and further cultures were made. 



After this the fimgus was a second time isolated from 

 diseased twigs in a method agreeing well with the above. 



Pycnidia of the fimgus were first noticed on 19th October, 

 1914, in an oatmeal agar plate poured on the 31st August, 1914. 

 The medium had entirely dried up, and there were raised hum- 

 mock-like l:)odies, often aggregated together, in which were 

 found typical Cysfospora spores (PI. 2^. a). As the fungus was 

 now definitely determined as being the one on the apple twig, it 

 was possible to proceed further. 



