290 



COMPARATIVE MORPHOLOGY OF FUNGI 



high. Each of the ultimate branches is slightly swollen and contains 

 a single perithecium with a firm, carbonaceous wall (Moeller, 1901). 



The last genus of the Xylaria group, Poronia (Fig. 190), differs from 

 Xylaria and Thamnomyces by the discoid expansion of its fertile part. 

 Its best known species, Poronia punctata, is found in the northern hemi- 

 sphere on old horse dung, from which often only its fertile disc protrudes. 

 In youth it is covered with light gray conidia. Later, at different times, 

 helical ascogonia which end in a trichogyne, as in Poly stigma, are formed 

 in spots and develop in an unknown manner (Dawson, 1900). 



Summary. — Here we have finished our forced march through the 

 steppe of the Sphaeriales. In this order, especially in their parasitic 

 representatives, pleomorphism (richness of various imperfect forms) 

 reaches its highest point. The perfect forms are developed during the 

 winter in our climate, where they are hastened to maturity by alternate 



Fig. 190. — Poronia punctata. Longitudinal section of a stroma. (After Tulasne.) 



wetting and drying, and hindered by the cold of winter until spring 

 begins. Their sexual organs incline toward the Plectascales type, as 

 do the Hypocreales, and, as the latter, still possess active antheridia. 

 Besides they show, e.g., in Sordaria macrospora type, wholly new pecul- 

 iar forms whose significance is at present unknown. The form of fructi- 

 fications vary as in the Hypocreales and, like them, attain to aggregate 

 fructifications which begin with simpler Nectrioid cushions and ascend 

 to highly individualized, possibly perennial stromata like Cordyceps. 

 Many Sphaeriales live in consort with algae and form the Pyreno- 

 mycetous lichens, whose fungus components are still of uncertain 

 relationship, 



