104 DISEASES OF TREES 



perfectly rotten before the berries themselves are attacked. The 

 diseased berries soon assume a pale colour, and the yellowish 

 white appearance is so characteristic as to have suggested for 

 the disease its popular American name of " White-rot," to 

 distinguish it from the dark discoloration induced by Black- 

 rot. So far no effective method of treatment has been 

 discovered. 



Grloeosporium ampelophagum (Sphaceloma ampelinum} 

 produces the " Anthracosis " of the vine. On all parts of the 

 plant are observed brown blotches which rapidly become black. 

 These soon turn to depressions surrounded by a ridge. Later 

 on, when the blotches and surrounding tissues dry up, projecting 

 portions of the mycelium bearing gonidiophores make their 

 appearance on the surface as small white spots. Pycnidia are to 

 be found in the ridge. Anthracosis finds the conditions best 

 suited to its development in warm situations after prolonged 

 damp weather. 



Didymosphaeria populina attacks the Lombardy poplar, and 

 produces a disease which is met with in many parts of France 

 and Germany. 1 



In spring a brown blotch on one side of the young twigs 

 situated on the lower branches indicates the point to which the 

 mycelium of the fungus has extended. A little later all that 

 portion which is situated above the original blotch becomes 

 black and bends inwards. The buds situated below the diseased 

 spot produce fresh shoots, which become infected in the following 

 spring. Branches whose shoots are largely infested wither up 

 entirely. The lower part of the tree, which suffers most from 

 the disease, becomes very bushy owing to the abundant 

 production of suckers, consequent on the stimulus imparted 

 to the buds by the destruction of the shoots. These sucker- 

 shoots ultimately succumb to the same fate as their predecessors. 

 As a consequence of this state of things, all the nourishment 

 is used up in that part of the tree, with the result that the top of 

 the infected tree withers before the parasite has ascended so far. 

 In the month of May the pycnidia begin to break through the 

 epidermis to admit of the escape of elliptical hyaline stylospores, 



1 Vuillemin, Compt.Rend.2$\h. March, 1889, and Prillieux, ibid. 27th May, 

 1889. 



