PERIOLA. 



[ 498 ] 



PERTUSARIA. 



horns, to form the single genus Peridinium, 

 placing those with horns in a genus Cera- 

 tium. 



BIBL. Ehrenberg, Infus. p. 252 ; Dujardin, 

 Infus. p. 374 ; Allman, Micr. Journ. iii. 24. 



PERIOLA, Fries. P. tomentosa, Fr., 

 described as a Sclerotioid Fungus, is an 

 obscure, irregular, fleshy body, with a white 

 villous surface, found growing on potatoes. 

 It is probably the early form of some unas- 

 certained species of fungus. 



PERIPTERA, Ehr. A genus of Diato- 

 maceae. 



Char. Frustules single, compressed; valves 

 circular, dissimilar, one being simply turgid, 

 the other winged or furnished with horns ; 

 horns sometimes branched and attached to 

 the extreme margin. Fossil. 



Valves not areolar nor punctate under 

 ordinary illumination. 



Four species. America and Bermuda. 



BIBL. Ehrenberg, Ber. d. Berl. Akad. 

 1844. p. 263; Kiitzing, Sp. Alg. p. 25. 



PERISPORACEL A family of Ascomy- 

 cetous Fungi, mostly epiphytic and of small 

 size, characterized by producing floccose 

 common receptacles (mostly) radiating from 

 a point, forming patches upon leaves, &c., 

 in the centre of which are developed some- 

 what globular perithecia, of obscure cellular 

 structure, persistent, bursting at the summit, 

 filled densely with subgelatinous, scarcely 

 diffluent gelatine; sporidia produced in asci, 

 subsequently often effused, simple, free, and 

 mixed with the gelatine in the centre of the 

 perithecium. The mycelia of these plants, 

 bearing conidial structures, have been de- 

 scribed as distinct fungi, for example those 

 of Erysiphe, as Oidia, &c. See ERYSIPHE. 



Synopsis of British Genera. 



I. LASIOBOTRYS. Perithecium fleshy- 

 horny, globular, naked, collapsing at the 

 summit. 



II. ERYSIPHE. Perithecium membranous, 

 closed at first, afterwards open, supported 

 on a persistent radiating mycelium, formed 

 of continuous filaments, bifid at their ends. 

 Asci four or eight, paraphyses none ; spores 

 continuous, ovate. 



III. PERTSPORIUM. Common receptacle 

 floccose. Perithecium superficial, at length 

 bursting irregularly. Asci club-shaped, not 

 mixed with paraphyses. Spores simple, 

 ovate. 



IV. CH.ETOMIUM. Common receptacle 

 floccose. Perithecium superficial, finally 

 open at the mouth, clothed externally with 



opake hairs. Asci clavate, mixed with para- 

 physes. Spores simple, ovate. 



V. ASCOTRICHA. Perithecium thin, at 

 length bursting, clothed with dark, subpel- 

 lucid, even, obscurely-jointed hairs. Spores 

 simple, contained in linear asci. Superficial, 

 at length free or resting on the investing 

 thallus, black. 



PERISPORIUM, Fr. A genus of Peri- 

 sporacei (Ascomycetous Fungi), consisting 

 of minute, globular, free, punctiform sacs, 

 with fleshy or waxy walls, seated on an obscure 

 thallus, growing on leaves or stalks j finally 



Fig. 563. 



Fig. 564. 



Perisporium disseminatum. 



Magnified 



Fig. 564. An ascus detached. Magnified 300 diams. 



Fig. 563. A perithecium in vertical section 

 100 diameters. 



bursting and collapsing. The spores are 

 produced in large numbers in swollen clavate 

 asci (figs. 563, 564), which are accompanied 

 by paraphyses. 



BIBL. Fries, Summa Veg. p. 404, Syst. 

 Myc. iii. p. 248 ; Berk. Ann. Nat. Hist. vi. 

 p. 432. 



PERITHECIUM. The name applied to 

 the special envelope, mostly of different 

 structure from the rest of the thallus or the 

 receptacle, enclosing the " nucleus " of the 

 Angiocarpous Lichens and the Pyrenomyce- 

 tous Fungi. 



PERITONEUM. See SEROUS MEM- 

 BRANES. 



PERONOSPORA, Ung. See BOTRYTIS. 



PERTUSARIA, D.C. A genus of En- 

 docarpeae (Angiocarpous Lichens), having an 

 adnate, uniform thallus, spreading over bark, 

 rocks, &c., and bearing wart-like apothecia, 

 finally exhibiting a depressed pore in their 

 centre, leading to the one or several cells 

 containing the theca?. P. communis is very 

 common on trees. 



BIBL. Hook. Brit. Flor. ii. pt. 1. p. 164 ; 

 Engl. Botany, pi. 677 ; Leighton, Brit. 

 Angioc. Lichens, p. 26. pis. 9-11. 



