244 



ASCOMYCETES. 



The disease is best combated by prompt removal of fallen 

 leaves in autumn; where this rule is followed Rhytisma is seldom 

 found (see p. 71). 



Rhytisma punctatum (Pers.) (Britain and U.S. America). 

 Whereas the spots of the Rhytisma just considered are large, 

 those of this species seldom exceed a few millimetres. They are 



FIG. 129 Rhytisma punctatum. Leaf of Acer Pseudoplatanvis with apothecia ; 

 the leaf is yellow, but the spots enclosing the apothecia are still green, 

 (v. Tubeuf del.) 



black in colour, angular, and scattered over the whole leaf- 

 surface. After the leaf has turned yellow, portions of it sur- 

 rounding spots of this Rhytisma retain their green colour, so 

 that we have black spots on green islands in the yellow leaf. 

 The sclerotia dehisce by valves. The apothecia contain thread- 

 like paraphyses and asci. The asci are club-shaped and contain 



