CHAPTER XIX 



HYSTERIALES 



With the Hysteriales begins the group of hemiangiocarpous Ascomy- 

 cetes; they are Pyrenomycetes with elongate perithecia, closed during 

 development, opening at maturity by a long slit which follows an earlier 

 dehiscence line and almost completely uncovering the hymenium (Fig. 

 193, y). This special form of perithecium is called a hysterothecium. 

 They appear depressed or conchoidal and have a carbonaceous or 

 2 membranaceous wall; often they are irregularly bent. 

 The longitudinal slit (a typical ostiole is lacking in 

 the true forms) penetrates the upper surface as a deep 

 groove. In damp weather, after complete maturity, 

 the walls open like lips, more or less closing in dry 

 weather. This process may be repeated many times. 

 On the base of the perithecium, the asci form a broad, 

 light-colored hymenium with paraphyses. 



The Hysteriales have the elongate opening in com- 

 mon with the Lophiostomataceae of the Sphaeriales. 

 According to the idea of Hoehnel (1918), these two 

 families should be united in a new order, the Hystero- 

 stomeae; but such a rearrangement should be deferred 

 until more ontogenetic and morphological information 

 is secured. At any rate, the present limits of the 

 Fig. 193. — Lopho- Hysteriales include entirely heterogeneous forms, 



dermium pinastri. on i • 1 • ,i <• , --it 1 ^ , • i i 



pine needles, a, one- which in the future will be removed to neighboring 

 year-old spots; b, two- orders. According to Lindau (1897), they may be 



year-old dead needles ...... _ .... 



with mature, x, and divided into five families: the Hypodermataceae, 

 empty, y, hysterothe- whose hysterothecia are embedded in the substrate, 



overgrown by a layer of host tissue with which they 

 form a clypeus; the Dichaenaceae, hysterothecia membranous — leathery; 

 Ostropaceae, hysterothecia thick, almost corky, at first embedded, later 

 erumpent and free; Hysteriaceae, hysterothecia carbonaceous, black; and 

 Acrospermaceae, hysterothecia horny, brown, free at the top, but with 

 the bottom somewhat embedded in a subiculum. 



Only a few Hypodermataceae are of economic significance, especially 

 Hypodermetta (ascospores unicellular, lachrymiform) Hypoderma (asco- 

 spores two-celled) and Lophodermium (ascospores unicellular, elongate) 

 which cause a premature drying and abscission of coniferous needles : L. 



296 



