244 



ASCOMYCETES. 



The disease is best combated by prompt removal of fallen 

 leaves in autumn; where this rule is followed Rlujtisma 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 Pseudoplatanus with apothecia ; 

 the loaf is yellow, but the spots enclosing the apotheci.a are still green. 

 (V. Tubcuf 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 Bhytisma 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 



