ONCOSPHENIA. 



[ 554 ] 



OOGONIUM. 



ficial ones crowded, forming a cortical layer. 

 3 species, brownish-green or purplish ; on 

 submersed wood and mosses. (Rabenh. 

 Alg. ii. 67.) 



ONCOSPHE'NIA, Ehr. A genus of 

 Diatomaceae. 



O. carpathica. Valves laxly striated, one 

 end turgid, rounded, and straight ; the other 

 attenuate and uncinate ; freshwater ; diam. 

 1-790". 



BIBL. Ehr. Ber. Berl. Ak. 1845, 72; 

 Kiitz. Sp. Alg. 11 ; Rabenh. Alg. i. 296. 



ONION, Allium Cepa (Flowering Plants, 

 Nat. Ord. Liliaceae). The young bulb of the 

 onion offers a very good and cheap subject 

 for the investigation of the development of 

 spiral vessels, to those who do not object to 

 its odour ; other bulbs will do equally well. 

 In the cells of the base of the Ibulb occur 

 very elegant groups of prismatic crystals 

 (see RAPHIDES). 



ONOCLEA, Sw. A genus of Dick- 

 soniese (Polypodiaceous Ferns). Sori dorsal, 

 globose, on the veins of changed contracted 

 pinnae of the fertile fronds, and concealed by 

 their revolute margins. 3 species ; cold or 

 temperate climates. (Hook. Syn. 45.) 



ONYCH'IUM, Kaulf. A genus of 

 Pteridese (Polypodiaceous Ferns). Four 

 species ; tropical. (Hook. Syn. 143.) 



ONYCHODROMUS, Stein. A genus of 

 Hypotrichous Infusoria. Like Stylonichia, 

 but the ventral styles linear, and the caudal 

 setae absent. O. grandis; freshwater. 

 (Kent, Inf. 766.) 



ONYG'E'NEL A family of Ascomyce- 

 tous Fungi, containing a few inconspicuous 

 plants growing upon the feathers of dead 

 birds, or upon cast-off hoofs and horns. The 

 flocculent spreading mycelium usually pro- 

 duces on its surface little white stalk-like 

 bodies crowned by a globular perithecium. 

 At first erect and thick, these supports be- 

 come more slender as they elongate, and 

 seem to bend under the weight of the light 

 perithecium (fig. 531). In some species the 

 perithecium is sessile. The perithecium is 

 Silled with branching filaments, arising from 

 the walls of its internal cavity, interlacing 

 together and bearing at their free extremi- 

 ties globular cells (asci) containing the 

 spores (figs. 633, 535). At the epoch of 

 maturity the perithecium, originally closed, 

 bursts circularly to wards the base, the upper 

 part becoming detached under the form of 

 a more or less regular cap (fig. 532), expo- 

 sing the spores set free by a solution of the 

 filaments. 



Fig. 531. 



Fig. 532. 



Fig. 533. 



Fig. 534. 



Onygena corvina. 



Fig. 531. Plants on a feather. Nat. size. 

 Fig. 532. Single plant with the perithecium dehiscing. 



Magn. 10 diams. 

 Fig. 533. Portion of the sporiferous layer, with asci. 



Magn. 350 diams. 



Fig. 534. Asci detached. Magn. 700 diams. 

 Fig. 535. Spores. Mag. 700 diams. 



British Genus. 



Onygena. Perithecium capitate, at length 

 slit round the base, and falling off' as an 

 imperforute cap. Asci borne at the free 

 ends of filaments forming an entangled mass 

 in the perithecium, finally free and pulvera- 

 ceous. 



BIBL. Berk. Br. Fl. ii. pt. 2. 322 ; Ann. 

 N. H. vi. 432, 2nd ser. vii. 184; Tulasne, 

 Ann. Sc. Nat. 3 s$r. i. 367, pi. 17 ; Greville, 

 Crypt. Fl. pi. 343 ; Cooke, Handb. 641. 



OOCAR'DIUM, Nag.,=7nomerm. 



OOCYS'TIS,Nag. A genus of Palmel- 

 laceous Algae, probably identical with 

 Nephrocytium. 



BIBL. Rabenh. Fl. Eur. Alg. iii. 52. 



OOGO'NIUM. A term sometimes used 

 to signify the parent cell of a true female 

 spore. 



