HEMISPHAERIALES 301 



cushion which has only a covering and no specially differentiated basal 

 layer. Seen from above, its development appears as if a round or 

 elliptical portion of the thallus arches up and begins to thicken, while 

 an ascigerous hymenium forms under the arch. This process is called 

 pycnosis in systematic literature, and the fructifications thus formed 

 pycnothecia. In the second place, the formation of ascogenous hyphae 

 is preceded by a true sexual act, which on the whole takes place in organs 

 of a structure like that of Claviceps purpurea of the Hypocreales. In 

 the third place, under the same cover layer, several ascogonia may be 

 active, so that under certain conditions the ascogenous hyphae radiate 

 from several centers. This last peculiarity suggests a tribe of the Stig- 

 mateaceae, the Munkielleae, ontogenetically still unknown, which, with 

 a structure otherwise the same, has under the same cover several hollow, 

 arched discs of asci. 



Polystomellaceae. — This family is characterized by its ascomata 

 arising only on the surface while the mycelium is parasitic in the interior 

 of the leaf. They show a great similarity to the Coccoideae and Leveillel- 

 leae of the Dothideaceae. They may be briefly described as Coccoideae 

 or Leveillelleae with radial cover layers. As in the Coccoideae, so also in 

 certain Polystomellaceae, the fructifications are rooted in the host tissue 

 by a central column; in other Polystomatellaceae, as in the Leveillelleae, 

 several of these columns may be present. 



According to the outline of the loculi, the family may be divided into 

 two tribes, the Polystomelleae with round, and the Parmulineae with 

 linear loculi. This distinction, however, is only of value for mature 

 perithecia; thus in many species of Hysterostomella the young loculi at the 

 edge of the turf are round, developing their linear outline only at maturity. 

 In this linear outline of the Parmulineae, people have tried to see a rela- 

 tion to the linear opening of the Hysteriales, and hence have called the 

 Parmulineae Hemihysteriaceae. It seems here to be a question of con- 

 vergence phenomena, however, for from the irregularly tearing slit of 

 the Parmulineae to the labiate opening of the typical Hysteriales, the 

 step is just as great as from the opening of the Dothideales to the ostiole 

 of the typical Sphaeriales. In any case the originally circular perithecium 

 shows a further development. 



Hysterostomella discoidea (Parmularia discoidea, Schneepia discoidea) 

 corresponds to the Leveillelleae type of the Dothideales. In West Java, 

 it is parasitic on fronds of Polypodiwm longissimum and there forms more 

 or less circular stromata up to 3 mm. in diameter. The infected leaf 

 surface is slightly vesicular and the stroma arches over convexly. In the 

 hypostomatal cavities, the hyphae collect in brown or violet tangles, and 

 then push outward to the leaf surface in perpendicular prosenchymatic 

 columns (Fig. 199). Here they expand horizontally. Generally the 

 hyphal bundles are only present in the central portions of the stroma 



