330 COMPARATIVE MORPHOLOGY OF FUNGI 



The Rhizinaceae and Pyrenemaceae form the gymnocarpous stage; 

 the former ascend from simple, loose layers to tuberous, tortuous fructi- 

 fications, the latter develop to typical apothecia of the Pezizales. 



Rhizinaceae. — The lowest stage is Ascocorticium whose representa- 

 tives form thin membranes of whitish or reddish color on bark, etc., such 

 as we shall meet in the Corticiaceae of the Basidiomycetes. On these 

 coverings, there is laid an even hymenium of eight-spored asci without 

 paraphyses. Perhaps the curious Medeolaria Farlowi on Medeola 

 virginiana belongs here. The indeterminate hymenium spreads over 

 the epidermis of the host, producing many fascicles of paraphyses but 

 few asci with dark brown, striate spores (Thaxter, 1922). Unfortunately 

 the ontogeny of these forms is not yet known. 



A higher stage is taken by Rhizina, whose original flat fructifications, 

 later generally arched upward, have the consistency of fleshy crusts. 

 R. undulata forms luxuriant white mycelia on the roots of many forest 

 trees. Later these intertwine on the roots or on the earth to small hyphal 

 tangles whose peripheral ends show a tendency to form a palisade, later 

 a paraphyseal layer. When these knobs have attained a cross-section 

 of about 1 mm., as many as eight ascogonia form in their interior. From 

 the beginning, these are multinucleate and arise from ordinary vegetative 

 hyphae. These wind loosely through the other hyphae and consist of 

 ten to nineteen or more cells (Fig. 218, 2). The terminal cell is small 

 and pointed; its content is early disorganized; possibly it is a functionless 

 trichogyne. When the ascogonia have matured, large pores are formed 

 in the septa so that the cells come into open communication with each 

 other. About half of the cells, chiefly those which lie in the middle of 

 the ascogonium, develop now into ascogenous hyphae (Fig. 218, 3) into 

 which flows the protoplasm of the remaining basal cells (Fitzpatrick, 

 1917, 1918). 



The highest stage is shown by the Sphaerosoma group (Rouppert, 

 1909; Setchell, 1910) whose fructifications are generally hidden in the 

 forest between dead leaves and, on account of their tuberous form and 

 fleshy mass, are often considered truffles. Their earliest stage corre- 

 sponds in structure to the simple apothecial scheme (Fig. 219, 1). Then, 

 however, the hymenium develops very strongly towards the sides, conse- 

 quently the edges of the cup arch downwards and often form an indented, 

 folded, hollow sphere up to 3 cm. in diameter, which in S. fuscescens 

 (S. Janczewskianum) and S. echinulatum show their origin from a stipe 

 (Fig. 219, 2). The hymenium develops hemiangiocarpously on the 

 exterior of this hollow sphere (while the interior remains a sterile hypo- 

 thecium) and consists of asci and paraphyses, which latter often inter- 

 twine over the tips of the asci. In the closely related Sphaerozone 

 ostiolatum {Sphaerosoma fragile) , having verrucose instead of echinulate 

 spores, development has been reported as gymnocarpous. In another 



