SPHAERIALES 287 



a conidial hymenium but later become brittle, hard and carbonaceous. 

 A related species, U. zonata, causes a root disease of Hevea and tea. 



In the higher genera these external stromata, as in the higher Hypo- 

 creales, gradually attain characteristic limits and become true fructifi- 

 cations. At first they arch in the middle and become hemispherical or 

 (as in Mycocitrus and its relatives) tuberous, e.g., in Hypoxylon (Fig. 187) 

 and Daldinia; but one may not draw a sharp line between these two 

 genera and Ustulina as their stromata, especially in immature specimens, 

 often still remain resupinate crusts. The mycelia of both these genera 

 exhibit very beautiful, graceful, often characteristically branched conidio- 

 phores whose spores in Hypoxylon unitum are lateral on the conidiophores 

 and in H. fuscum and H. coccineum are terminal in a solid little head. 



^^ 



Fig. 187. — Hypoxylon coccineum. Fructifications in various stages of development, the 

 youngest still bearing conidia. {After Tulasne.) 



Coremia also occur. Usually the conidiophores are scattered over the 

 whole mycelium; more rarely their appearance is limited to the sur- 

 face of the young stroma. They are always present there, however, 

 and by the mass of their spores give it a powdery appearance and a 

 peculiar color often differing from that of the mature fructification. In 

 all cases the perithecia develop after the disappearance of the 

 conidial fructification. Both genera inhabit, mainly, rotting wood 

 and dry branches. In Hypoxylon the stromata are homogeneous, in 

 Daldinia in concentric layers; this distinction is rather quantitative, 

 however, and only reliable in extreme forms; thus the tropical D. exsur- 

 gens shows a slight zonation but is otherwise similar to Hypoxylon. 



In the highest genera, as Xylaria, Thamnomyces and Poronia, as in the 

 highest Hypocreales, there begins the differentiation of the stromata into 

 a sterile and fertile part. Xylaria is cosmopolitan, but especially well 

 represented in the tropics. It generally inhabits dead wood, rarely dung 



