208 



INTRODUCTION TO THE STUDY OF FUNGI 



Euryachora the stroma is broadly effused and punctulate, whilst 



in Homostegia the stroma is plane or hemispherical, and the 



species are parasitic upon 

 Lichens. In Rlwpographus 

 the stroma is elongated and 

 linear, suggesting a resem- 

 blance to some Hysteriaceous 

 perithecia. Species of Phyl- 

 lachora are common on cori- 

 aceous leaves in tropical coun- 

 tries, and are sometimes 

 difficult to distinguish at 

 first from some of the Rhy- 

 tismoideae. In common with 

 the latter the stroma is often 

 present for some time before 

 the fructification is developed, 

 hence they are often met with 

 in a sterile condition. 



The subfamily Rhytis- 

 moideae is included by some 



authors with the Discomyceteae, on account of the mode of 



dehiscence, which is usually by gaping fissures, so that the 



hymenium is more or less exposed ; but this dehiscence does 



not take place until the sporidia are 



fully mature, and sometimes not until 



disintegration has commenced. In 



external appearance the species are 



very similar to Phyllachora and Eury- 



achora, and yet in texture of the 



stroma, and often in the fructification, 



appear to be more closely allied to 



the Dothideaceae than to any family 



of the Discomyceteae. Practically, the 



only genus is Rhytisma, for the sporidia 



of so many described species are 



unknown that no proposals have been 



possible to divide them into genera based upon the fructifi- 

 cation. Such a species as Rhytisma acerinum, which is common 



Fig. 97. — Daldinia, globose stroma and 

 section. Oard. Ghron. 



Fig. 



Hypoxylon. 

 sporidia. 



Globose stroma of 

 with asoi and 



