ONYGENEI. 



[ 471 ] 



OPALINA. 



nal cavity, interlacing together and bearing 

 at their free extremities globular cells (asci) 

 containing the spores (figs. 538. 540). At 



Fig. 536. 



Fig. 537. 



Fig. 538. 



Fig. 539. 



Onygenei corvini. 



Fig. 536. Plants on a feather. Nat. size. 



Fig. 537. Single plant with the perithecium dehiscing. 



Magn. 10 diams. 

 Fig. 538. Portion of the sporiferous layer, with asci. 



Magn. 350 diams. 

 Fig. 539. Asci detached. Magn. 700 diams. 

 Fig. 540. Spores, Magn. 700 diams. 



the epoch of maturity the perithecium, ori- 

 ginall}" closed, bursts circularly towards the 

 base, the upper part becoming detached un- 

 der the form of a more or less regular cap 

 (fig. 537), exposing the spores set free by a 

 solution of the filaments. 



British Genus. 



Onygena. Perithecium capitate, at length 

 slit round the base, and falling off" as an im- 

 perforate cap. Asci borne at the fi*ee ends 

 of filaments forming an entangled mass in 

 the perithecium, finally free and pulvera- 

 ceous. 



BiBL, Berk. Brit. Flora, ii. pt. 2. p. 322, 

 Ann. Nat. Hist. vi. p. 432, 2nd ser. vii. p. 

 184; Tulasne, Ami. des Sc. nat. 3 ser. i. p. 

 367. pi. 17; Greville, Sc. Crypt. Fl. pi. 343. 



OOLITE. — The substance of ooUtic rocks 

 consists principally of carbonate of lime, 

 sometimes crystallized, at others granulai', 

 and usually abounding in organic remains, 

 as shells, &c. It consists of two parts, one 

 of which forms the matrix, is mostly colour- 

 less, often crystalline, and exhibits a number 

 of rounded or oval cavities, each of which 

 contains a nodule, or mass of a correspond- 

 ing form. These nodules give the stone 

 somewhat the ajjpearance of the roe of a fish, 

 hence oolite is sometimes called roe-stone. 

 The nodules possess rather a granular than 

 a crystalline structure. They are sometimes 

 colom'ed, hollow, and often exhibit concen- 

 tric rings like those of calculi, and indicative 

 of the successive deposition of layers. Some 

 kinds of oolite contain grains of sand im- 

 bedded in the matrix between the nodules. 



Polished sections of oolite form interest- 

 ing objects; and where the nodules ai-e co- 

 lom'ed and the matrix colourless, as in oolite 

 from Bristol, in which the former are red, 

 the beauty of the appearance is increased. 



BiBL. Works on geology (see the Bibl. 

 of Chalk). 



OOMYCES, Berk, and Br.— A genus of 

 Sphaeriacei (Ascomycetous Fungi), founded 

 on a minute plant growing upon the leaves 

 of grasses. 0. carneo-albus {Sjjhceria car- 

 neo-alba, Libert.) has pale, flesh-coloured, 

 tough receptacles 1-18" high, marked with 

 the ostioles of 3-7 perithecia closely packed 

 within it, bearing resemblance to the eggs of 

 some insects. 



Bibl. Berk. & Broome, Ann. Nat. Hist. 

 2 ser. vii. p. 185. 



OOSPORANGES.— The name apphed 

 by Thm-et to the organs (called ' spores ' by 

 most authors) producing the larger kinds of 

 zoospores, in those tribes of Algse where 

 zoospores of two sizes occur (see fig. 462, 

 p. 424). These organs are usually ovate, or 

 of some analogous form ; those containing 

 the smaller zoospores are usually filiform, 

 and are distinguished as trichosporanges. 

 The term is also applied, together with 

 oophoridiuni, to the sporanges containing 

 the larger spores in Selaginella and 



ISOETES. 



OPALINA, Purk. and Val.— The animals 

 comprised under this title were formerly re- 

 garded as Infusoria, among w hich they were 

 placed, but later researches tend to show 

 that they are imperfectly developed forms 

 or intermediate stages of animals probably 

 hioher than the Infusoria. Thev are micro- 

 scopic, oval or oblong, colom'less, covered 



