S8 



Br^ITISIl FUNGI 



is the conidial or summer-fruit which is produced on the surface 

 of the leaf, so that the conidia may be dispersed and infect neigh- 

 bouring plants. 



At the same time that the fungus is producing its summer-fruit 

 on the surface of the leaves, its mycelium grows down the inside 

 of the stem, passes along the inside of the underground branches, 

 and finally enters the tissues of the young potatoes or tubers. 

 When tubers containing such hibernating mycelium are planted, 

 the mycelium grows up along with the stem, enters the leaves, and in 



"Wiiclies'-broom " from an alder tree, produced by a 

 fungus called Exoasais ttu-gidiis. 



due course produces summer-spores ; some of the mycelium also 

 passes along the underground branches and enters the new tubers, 

 which thus become infected, and in turn produce another diseased 

 crop when planted. As a rule, tubers containing mycelium can be 

 recognized by the presence of brownish patches on the surface, 

 or in the substance of the' flesh, but this is not always the case, 

 and the mycelium may be present without any obvious dis- 

 coloration of the tuber. This accounts for many outbreaks of 

 potato disease when tubers apparently sound were planted, and 

 when no disease was present in the district that could furnish 

 summer-spores for infection. It may naturally be asked. If tubers 



