PLOWRIGHTIA 213 



is dead or nearly so, when numerous elongated, large black 

 stromata or warts burst through the bark, always transversely 

 to the long axis of the branch. These warts are often 

 crowded, giving a blackened appearance to the branch. 



Stromata black, minutely warted owing to the slightly pro- 

 jecting mouths of the loculi, which form a single crowded 

 row at the periphery : asci 8-spored ; spores elongato-fusiform, 

 ends pointed, septum median, yellowish, 18-21 X 5-6 /*. 



Fuckel considers that Dothiorella ribis, Saec. {=Podo- 

 sporiumribis, Fuckel) is a conidial condition of this species. 

 Saccardo, on the other hand, says D. ribis is a condition of 

 Diaporthe strumella (Fckl.), another ascigerous fungus growing 

 on dead branches of gooseberries and currants. This point 

 remains to be definitely settled. I have never found 

 Dothiorella in Britain. It is characterised as follows : 

 Perithecia few, immersed in a black stroma, which forms a 

 prominent pustule ; spores on short pedicels, ovate-oblong, 

 often curved, hyaline, simple, 30 X 14 /^, expelled as a white 

 mass. 



Spraying is useless in the present instance. When the 

 disease first appears, which is indicated by the wilting of the 

 foliage, infected branches should be removed and burned. 

 Aphides and currant scale should be kept down by the use of 

 suitable spraying solutions. 



Massee, G., Gard. Chron. 



Black knot. One of the most dangerous of diseases to 

 which plum and cherry trees are subject is caused by a fungus 

 called Plowrightia morbosa (Sacc). This pest up to the 

 present is confined to the United States and Canada, but 

 there is the possibility of its introduction into Europe or other 

 parts of the world at any moment. 



The fungus forms large, nodulose, black excrescences on 

 the branches, which are often bent or otherwise distorted at 

 the point of injury. The excrescences often extend for 

 several inches along the branch. A conidial condition of the 

 fungus first appears bursting through cracks in the bark. 

 This is followed by the growth of a swollen, irregularly 

 nodulose, hard stroma, black externally, and minutely 

 granular, due to the projecting mouths of the embedded 

 perithecia. 



Conidiophores forming a dense, blackish-olive, velvety pile ; 



