198 INTRODUCTION TO THE STUDY OF FUNGI 



coriaceous, or hard and carbonaceous, and usually black. 

 Dehiscence may take place by means of an apical pore or 

 mouth, occasionally elongated but more commonly circular and 

 dot-like ; or the perithecium may be absolutely closed, and 



when mature, splitting irregularly. 

 In all cases the rapture only takes 

 place at maturity, to permit of the 

 escape of the sporidia. As to 

 habit, in some species the individuals 



Fig. 86. — Perithecium and section. . . 



are absolutely isolated and simple, 

 and either scattered or gregarious ; whilst in others they are 

 collected upon a pulvinate, or more or less strongly developed 

 stroma, which may be of variable form and magnitude, and 

 in this condition are characterised as compound. The large 

 majority are saprophytic, but a few are parasitic, and the 

 former occur most commonly on dead or decaying wood, 

 branches, twigs, fruits, leaves, or the dead parts of herbaceous 

 plants ; the latter are mostly confined to living leaves, or the 

 green parts of growing plants. Other details will follow more 

 conveniently under the several families. 



The Perisporiaceae may occupy the first place, in that they 

 are entirely simple, or with the perithecia separate from each 

 other, and not combined in a common stroma ; sometimes 

 membranaceous, at others coriaceous or tough, or more rarely 

 hard and brittle ; but their most distinguishing feature consists 

 in the wholly closed, or astomous, perithecia, which are 

 irregularly split when mature to permit of the escape of the 

 sporidia. It will be most convenient to review the details 

 under the several subfamilies, the first of which, at least, is a 

 compact and natural group. The Erysipheae are of parasitical 

 habit, and flourish on the living leaves and green parts of 

 arborescent and herbaceous plants. In the first instance a 

 web-like mycelium effuses itself broadly over the parts attacked, 

 and in this condition the leaves assume a white and mouldy 

 or chalky appearance, as if powdered with flour. In this stage 

 the delicate threads of mycelium, like a spider's web, interlace 

 each other, are repeatedly branched, and adhere closely to the 

 surface by the means of haustoria or suckers. From this 

 mycelium arise erect fertile branches, which become differen- 



