HYMENOMYCETES. 49 



Pilacre Petersii, Berk, and Curt., Ann. Nat. Hist., n. 824 ; 

 Sacc. Syll. 4, n. 2572. 



On trunks of hornbeam, holly, beech, &c. Gregarious, 

 often covering half-dead trunks for a considerable distance. 



HYMENOMYCETES. 



In tracing the evolution of the sporophore from the most 

 primitive, entirely resupinate forms, I have repeated what I 

 previously wrote on this subject.* 



" Eveiy type of hymenophore known in the Hymenomy- 

 cetes is met with in such genera as Stereum and ThelepJiora, 

 and in some instances even in the same species. 



The following are the most marked phases of sporophore 

 evolution as occurring in the Hymenomycetes, illustrated by 

 Stereum hirsutum, Fries, one of the Thelephoreae : 



(a) The most primitive type is where the sporophore is 

 spread out as a thin layer attached to the substratum by the 

 whole of the under surface, the upper surface being covered 

 with the hymenium. In many of the simpler Thelephoreae 

 this mode of growth is permanent ; but in species like Stereum 

 Jiirsutum, which may be described as inclined to ' sport,' or, 

 more correctly, where epinasty, the cause of the (a) type of 

 sporophore, is strongly manifested, the above mode of growth 

 occurs when developing on a broad horizontal substratum. 



(6) When the substratum is vertical, which may be the 

 side of a prostrate trunk, or an erect one, growth commences 

 as in type (a), and after extending from a centre for some 

 time, and assuming a more or less circular outline, the upper- 

 most margin becomes free, and continues to grow away from 

 the substratum, and at right angles to the attached portion. 

 In this type we get the first transition from the superior to 

 the inferior hymenium imperfectly indicated ; and it is in- 

 teresting to remember that the first step towards the inver- 

 sion of the hymenium itself the most pronounced result of 



* 'A Monograph of the Thelephoreae.' Part I., Linn. Soc. Journ. 

 Botany, vol. xxv. p. 107 (3 pi.). 



VOL. I. E 



