220 



COMPARATIVE MORPHOLOGY OF FUNGI 



while in the higher Dothioraceae, one would rather consider the single 

 conceptacle-bearing branches which grow out of the stroma as 

 fructifications. From the perithecia of the Perisporiales (and of the 

 Sphaeriales), these fructifications of the Pseudosphaeriaceae, except for 

 the special question of opening, are distinguished by the fact that in the 

 former the pore tissue of the perithecium is entirely resorbed during 

 development while in the latter, as in all the other Myriangi ales, it remains 

 as interthecial pseudoparaphyses (Hoehnel, 1909; Theissen, 1916; 

 Theissen and Sydow, 1918; Petrak, 1923). 



An illustration of the fructification of this family is shown in Pyre- 

 nophora (Fig. 144) and Pleospora (Fig. 145, 1). The fructifications are 

 small and like perithecia; they are immersed in the host and liberated by 



Fig. 145. — Pleospora herbarum. 1. Section through an immature peri', hecium ( X 250). 

 2. Conidiophore (Altemaria type) (X 135). 3. Germinating conidium ( X 2.35). (After 

 Arnaud, 1918, and Brefeld, 1881.) 



the rupture of the epidermis. They consist of a pseudoparenchyma 

 which is thick walled and dark colored in the two or three outer layers 

 of cells (outer crust) but on the inside has a more delicate structure. 

 In the middle of the stroma, each of the elongate asci develops in its own 

 core cavity. By the increase of asci in the course of development, the 

 intermediate hyphal bundles are compressed as far as possible and 

 finally remain only as thin, flabby paraphysoids merging into the stromatic 

 cover. The top of the perithecium eventually becomes more or less 

 markedly papilliform. It opens by the crumbling and falling away of 

 the papillae, giving the appearance of opening by a round pore. 



While in Pyrenophora at present only saprophytes are known, 

 Pleospora (numbering about 300 sp.) includes several plant pathogens, 

 as P. herbarum on many stems and fruits, P. Hyacinthi, the cause of the 



