Seasonal Notes. — September 219 



spots begin to appear in June, and towards the end of July 

 become very conspicuous. The leaves look as if they had 

 been splashed with tar. When a tree is attacked, usually 

 nearly every leaf is more or less spotted, and the number of 

 spots on each leaf may reach thirty or even more. They 

 begin with a yellowish discoloration, of a roundish form, 

 about a quarter of an inch in diameter. The yellow spots 

 are caused by the influence of the mycelium of the fungus on 

 the chlorophyll of the leaf, this mycelium grows centrifugally, 

 just beneath the epidermis, probably from a stomate, and 

 destroys the colour of the chlorophyll as it advances. It is 

 confined to the yellow spot, in the still green parts of the 

 leaf no mycelium can be detected." Small round black dots 

 next appear on the yellow areas, they increase and become 

 confluent, until the spot is quite black excepting a narrow 

 yellow border at its edge. " This is all that is produced of 

 the fungus so long as the leaf remains attached to the tree ; 

 but after its fall further changes begin to take place. This 

 is shown by a thickening and blackening of the affected part 

 of the leaf, so that about the succeeding March the under- 

 surface of the leaf is also blackish, and the mass of mycelium 

 doubles or trebles the thickness of the leaf. The upper 

 surface of the spot, which at first was dull and even, now 

 becomes shining and wrinkled." In May the flexuous 

 wrinkles open and the cracks become revolute. The asci 

 containing the spores are ruptured and the latter are ejected 

 in a cloud. If spores settle on a young sycamore leaf the 

 hypha will enter with the tissues and thus the life-cycle is 

 again commenced. Leaves produced later in the year remain 

 free of disease and do not fall so quickly as diseased ones. 



Flies and Fungi. 



Many flies are subject to fungus epidemics in autumn, 

 especially in damp seasons. 



House-flies, apparently glued to the window pane by a 



