one or more pores which appear as black dots. Minute spores, 

 which readily spread the disease, are produced from the pus- 

 tules in great abundance. In damp weather they are extruded 

 through the spores as minute, coiled, tendril-like threads of a 

 white, pink or reddish colour. This is due to the fact that the 

 spores are held together by a mucilaginous substance. When 

 wetted by rain this substance is dissolved and the individual 

 spores are separated from one another and blown or washed, 

 away. The spores may be extruded from the pustules over a 

 period of several weeks but in dry weather spore-liberation is 

 practically at a standstill.* 



The conditions under which infection takes place have 

 been carefully examined in the case of the cherry disease, 

 and it has been found that* the fungus can only gain entrance 

 to the tree through a wound. If the wound contains no dead 

 wood the injury caused, is very slight, but if dead wood is 

 present, the fungus lives upon it first and afterwards invades 

 the living parts killing them as it advances. This is probably- 

 true for other fruit trees. Late frosts or other adverse condi- 

 tions not infrequently cause the death of small branches, or of 

 portions of large ones, whilst careless pruning results in similar 

 injury which lays the tree open to attack. Rank, ill-ripened 

 wood is probably particularly liable to be injured in this way. 



Peaches. Twigs killed by the disease have at first a dark 

 purplish skin which later becomes leathery and shades into 

 scarlet and purple. The affected areas finally change to a drab 

 colour and the skin becomes loose and wrinkled. Later the 

 spore-pustules of the fungus appear on the affected areas and 

 these exude their spores in minute, tendril-like threads as 

 described above. In Canada the Cytospora disease causes 

 severe cankers on the wood, but this type of injury has not been 

 observed in England. 



Apples. In the case of apple trees the disease may start 

 on the branches and spread downwards producing somewhat 

 similar effects to those described for peach trees. The colour 

 of the diseased branches varies from a lightish to a dark purple. 

 Not infrequently, however, in the case of apples, the fungus 

 first attacks the main branches, or even the trunk of the tree 

 near the ground, and produces cankerous wounds. This form 

 of attack is very much more serious than the ordinary form of 

 die-back since the disease extends more rapidly in the tissues, 

 and if the trees are not immediately attended to, they may be 

 completely killed within a year or eighteen months. 



* Both on plums and other trees another form of fructification, tke 

 ascigerous stage, sometimes develops on the large branches which have 

 been dead for a considerable time. The ascigerous stage belongs either 

 to the genus Valsa or Eutypella according to the species of Cytospora 

 which is present. The previous edition of this leaflet was confined to 

 the two forms. of the fungus Eutypella prunastri. It is now known that 

 this species is only one of several which cause die-back of fruit trees. 



