is the mycelium or " roots " of the fungus, similar to the white threads in 

 the soil of a mushroom-bed. Black specks which appear later contain the 

 spores or " seeds." The plant does not require leaves or chlorophyll (green 

 colouring-matter), as it lives on plant-food already prepared by the host 



Trees badly attacked by l>laok-iot canker*!. Note dead liiultM. 



plant. Black-spot canker is one of these fungi which is parasitic in its 

 habits, and by close examination with a microscope it is possible to find 

 the mycelium or roots ramifying through the diseased portion, and the 

 spores or seeds in their season near or on the surface of the cankered area, 

 as described below. 



INFECTION OF HOST AND GROWTH OF CANKER. 



The canker as seen in the summer before the surface begins to get 

 rough has practically completed growth, and during the remainder of the 

 season it develops the spores. The pustules which rise on the surface 

 usually indicate spore formation, and as the season advances they rupture 

 the epidermis, allowing the spores to escape when weather conditions are 

 favourable. The spores are contained in a gelatinous mass which is dissolved 

 in water. 



