PHACIDIALES 313 



tissue forms a long continuous plectenchymatic stroma. In the central 

 parts of the stroma, numerous hyphal tips rise within the limited region 

 from the plectenchyma, form a regular palisade and, after June, cut off an 

 enormous number of uninucleate conidia. Their pressure ruptures the 

 outer epidermal wall, pieces of which are occasionally raised by the 

 conidial mass as upon a column, and the conidia are liberated in a milky 

 drop. Morphologically, thus, R. acerinum does not form pycnia, as 

 systematic literature often states, but acervuli like Cryptomyces Pteridis. 



Like the conidial layer, the apothecia are formed in the epidermis of 

 the upper surface of the leaf, chiefly on the peripheral parts of the stroma. 

 The majority of them are formed de novo, but a few are laid down in the 

 exhausted acervuli. In the fall, the whole stroma changes to a sclerotic 

 tissue which blackens on the upper surface, less often on the under surface 

 (i.e., toward the palisade layer of the leaf). In the interior of the plec- 

 tenchyma are differentiated numerous apothecial cavities filled with loose 

 hyphal tissue and covered by a thick-walled, pitch-black epithecium (and 

 the outer epidermal wall) and below rest on a somewhat broader, brighter 

 hypothecium (with the inner epidermal wall). 



In each apothecial fundament are formed several ascogonia which 

 consist of a uninucleate stipe cell, 2 to 3 multinucleate ascogonial cells 

 and a uninucleate trichogyne cell. The septa between the ascogonial 

 cells break down, as in Ascobolus citrinus of the Pezizales (Fig. 227); the 

 nuclei pair parthenogamously and migrate into the ascogenous hyphae, 

 which coil and grow out again, as we have already seen in Aphanoascus 

 cinnabarinus of the Plectascales. Eight ellipsoidal ascospores are formed 

 and elongate to filaments. They may be shot up for 1 mm., probably as 

 a result of contraction of the stroma in dry weather. Thus the swollen 

 paraphyses (which are formed from the loose hyphal tissue between the 

 epi- and hypothecium) press the asci which in turn squeeze out the spores 

 and secure their dispersal by air currents. 



While the asci are still in the uninucleate stage in early spring, a dehis- 

 cence zone about 12 cells wide is formed in the middle of the apothecium 

 in the lower fourth of the epithecium. The cells of this zone become dis- 

 organized, causing a narrow slit which, by the degeneration of the 

 bordering apical layers, expands somewhat at the top. In the lowest 

 fourth of the epithecium, below the horizontal slit, lateral growth begins so 

 that this lower fourth arches downward into the apothecial cavity. By 

 this lateral growth the upper layer of the epithecium is ruptured. Finally 

 the pressure of the ascospores ruptures the lower wall layer under the split, 

 and the edges spring back, exposing the hymenium. Unfortunately 

 these relationships cannot be figured in this book, as the work of Jones 

 was only available to the author after the figures had been sent off for 

 reproduction. 



