io6 



Sycamore Leaf Blotch, 



[may, 



In this country the fungus appears to be mostly confined 

 to the tips of the shoots, which for a distance of 2 or 3 in. 

 present a brown and shrivelled appearance, somewhat similar 

 to that produced by an attack of " green fly." On such 

 shoots, if carefully examined, especially with the aid of a 

 magnifying glass, the brownish patches of mildew studded 

 with black winter fruit can be readily seen. 



The coloured plate is reproduced by permission of the 

 Department of Agriculture and Technical Instruction for 

 Ireland. 



The conspicuous black spots (Rhytisma acerinum, Fries.) 

 resembling blotches of pitch, so general on living leaves of the 

 sycamore and maple, are probably 

 Sycamore Leaf familiar to everyone, although not always 

 Blotch. associated with the work of a parasitic 



fungus. Towards the end of June, small 

 yellowish patches appear on infected leaves ; these patches 

 increase in size until they are half an inch or more in diameter, 

 and gradually darken in colour, until finally they become 

 almost jet-black, with a border of dingy yellow. The substance 

 of a fully formed patch is much thicker than that of the leaf 

 proper, owing to a crust formed by the fungus. The surface 

 of the patch is wrinkled or corrugated, and, during the summer, 

 produces myriads of very minute spore-like bodies, the function 

 of which is unknown. They have not been seen to germinate, 

 and seem incapable of causing infection. During the following 

 spring, after the dead leaves have been lying on the ground 

 throughout the winter, spores of another kind are produced 

 in the substance of the black patches ; these spores escape 

 into the air through gaping cracks, and if they happen to alight 

 on suitable young leaves, infection follows. 



A second fungus, called Rhytisma punctatum, also forms 

 large black blotches on living leaves of sycamore and maple ; 

 it is distinguished by the black patch not being continuous, 

 but composed of numerous minute distinct black spots, crowded 

 together on a yellowish groundwork. The two kinds are not 

 infrequently present on the same leaf. 



When the disease is present, almost every leaf on the tree 

 is infected, as a rule, consequently a considerable amount of 



