RHYTISMA 255 



been killed by the fungus, a dense weft of mycelium is found 

 at the root, which firmly binds together a mass of sand or 

 earth. This is due to outflow of resin. On careful examination 

 numerous filaments of hyphae are seen to spring from the 

 bark. The tissues of the soft bark and the cortex turn brown 

 and are killed. Hartig observed the production of immense 

 numbers of very minute sporules, about i-i"5 /*, borne on 

 very short stalks springing from the tips and sides of hyphae 

 that grew from the infected roots. 



The fungus should be collected and buried. As already 

 stated, it is often produced in abundance on old heaps of 

 sawdust, or on the sites of charcoal pits or fires. Most 

 abundant on a sandy soil. 



Hartig and Somerville, Text-Book of the Diseases of Trees 

 (Engl, ed.), p. 123 (1894). 



RHYTISMA (Fries.) 



Asophores elongated, lips gaping and exposing the pale 

 disc when mature ; asci clavate ; spores long and slender, 

 hyaline, continuous, arranged in a parallel fascicle in the 

 ascus; paraphyses very slender ; conidia usually produced. 



Forming large black patches on living leaves, conidia are 

 formed during the autumn, and ascospores the following 

 spring on the dead leaves. 



Sycamore leaf blotch (Rhytisma acerinum, Fries.) produces 

 the large black spots resembling blotches of pitch so common 

 on the living leaves of sycamore and maple, and familiar to 

 every one, although not always associated with the work of a 

 parasitic fungus. About the end of June small pale-green or 

 yellowish spots appear on infected leaves. These spots 

 gradually increase in size and change by degrees to a con- 

 tinuous patch of jet-black, surrounded by a dingy yellow 

 border. When fully formed the black patch is thicker than 

 the substance of the leaf proper, due to the formation of a 

 thin stroma by the fungus, the surface of which is wrinkled or 

 corrugated. During the autumn immense numbers of very 

 minute spore-like bodies, or spermatia, are borne in con- 

 ceptacles in the black stroma, whose use is unknown ; they 

 have not been observed to germinate, and are not capable of 

 promoting infection. They probably represent what were at 



