PROTECTION A(JAINST FUN<:l. 



J inch across appear on maple leaves, and turn black in 

 August, retaining a lighter tint on their borders. The leaves 

 fall earlier than is usual. On the fallen leaves during winter 

 and the following spring numerous sporocarps develop on the 

 black spots, and they open in long cracks in damp weather. 

 The spores which issue from them in the spring germinate on 



Fig. 236. Rhytisma acerinum, Fr., on a leaf of Norway Maple. The dark blotches 

 () are surrounded by a dead lighter coloured zone (b). 



the leaves and produce fresh spots as before. The parasite 

 appears to be an annual, and is very common. 



The damage done is mostly due to reduced assimilating 

 powers of the leaves and is relatively unimportant. 



Where the dead leaves are swept up and burned, as in parks 

 and gardens, the disease does not spread, but in places where 

 dead maple leaves are allowed to lie about in ditches, etc., it 

 may recur annually to the detriment of the beauty and shade 

 of the trees. 



