ZYGNEMACEiE. 



[ 696 ] 



ZYGOSELMIS. 



Z. cruciata with the spores in the transverse 

 processes ; if so, the subdivision above indi- 

 cated cannot stand. 



Probably other species exist in Britain, 

 but we cannot satisfactorily ascertain them. 



BiBL. Hassall, Brit. Fr. Algce, p. 160. pis. 

 38, 39 ( Tyndaridea) ; Kiitzing {Zygnema 

 and Zygogonium, in part). Tab. Phyc. v. 

 pis. 11-17, Spec. Alg. pp. 444, 445. 



ZYGNEMACE.E (PI. 5. figs. 16-28).— A 

 family of Confervoid Algae, consisting of 

 plants composed of articulated cylindrical 

 filaments, the cells of which often have the 

 green contents arranged in elegant patterns. 

 The principal mode of reproduction, whence 

 the family takes its name, is by Conjuga- 

 tion, followed by a mixture of the entire 

 contents of the united cells, and their con- 

 version into a spore. Other phsenomena 

 occur in some instances, such as the produc- 

 tion of ciliated zoospores, and small spore- 

 like bodies with a dense spinulose coat 

 (asteridia), but these appearances are not yet 

 thoroughly understood (see Spirogyra and 

 Mougeotia). 



Synopsis of British Genera. 



I. Spirogyra. Filaments simple, with 

 the green contents arranged in one or more 

 l^piral bands upon the cell-wall. Conjuga- 

 tion normally by transverse tubular pro- 

 cesses ; spores formed in one of the parent- 

 cells (or occasionally in both). 



II. Zygnema. Filaments simple, with 

 the green contents arranged in two globular 

 or stellate masses in each cell. Conjugation 

 by transverse processes; spores formed in 

 one of the parent-cells, or in the cross branch. 



III. Zygogonium. Filaments simple or 

 slightly branched, with the contents diffused 

 or arranged in two transverse bands. Conju- 

 gation by transverse processes ; spores glo- 

 bose, formed in the cross branches, or in 

 blind lateral pouches without conjugation. 



IV. Mesocarpus. Filaments simple, 

 with the contents diffused. Conjugation by 

 transverse processes, from which the fila- 

 ments become recurved; spores in the dilated 

 cross branches. 



V. Staurocarpus. Filaments simple, 

 with the contents diffused (or rarely in mo- 

 niliform lines). Conjugation by transverse 

 ]jrocesses, from which the filaments become 

 recurved ; spores (or sporanges) square or 

 cruciate, in the dilated cross branches. 



VI. Mougeotia. Filaments simple, 

 soon bent at intervals, contents mostly dif- 

 fused, sometimes in , several serpentine 



lines. Conjugation by the inosculation of 

 the filaments at the convexity of the angles ; 

 spores not satisfactorily known. 



Thwaitesia, Montague, resembles Zyg- 

 nema, in its stellate cell-contents, but the 

 spore (?) formed in one of the parent-cells 

 divides into four portions (perhaps not di- 

 stinct from Zygnema). 



ZYGOCEROS, Ehr.— A genus of Diato- 

 macese. 



Char. Frustules free, single, compressed ; 

 valves each with two horns. Marine. 



Five species ; some of them are perhaps 

 isolated frustules of Biddulphia. 



Z. rhombus (PI. 14. fig. 13). Frustules 

 turgid; valves rhomboid, angles rounded, 

 finely striated and granular. Length 1-288". 



BiBL. Ehrenberg, Abhandl. d. Berl. Akad. 

 1839. 131 ; Kiitzing, Bacill. 138, and Sp. 

 Alg. 139. 



ZYGODON, Hook, and Taylor.— A genus 

 of Orthotrichaceous Mosses, deriving its 

 name from the yoking of the teeth in pairs ; 

 the species are mostly found in mountainous 

 districts and rarely in fruit. 



ZYGOGONIUM, Kutz.— A genus of 

 Zygnemaceae (Confervoid Algae), consisting 

 of filamentous plants, growing on damp 

 ground or in water, green or yellowish when 

 fresh, purple or brownish when dry. 

 Kiitzing includes here all Hassall's species i 

 of Tyndaridea (Zygnema) which produce 

 the spore in the cross branch. 



Z. ericetorum, Kiitz. Filaments 1-2160 

 to 1-1440" in diameter, joints as long or half 

 as long again ; cylindi'ical or torulose (fila- 

 ments sometimes slightly branched). Con- 

 jugation rare, apparently mostly ' chain-like,' 

 from one cell to the next in the same fila- 

 ment. Contents green when growing in ^ 

 water, purple when growing on wet heaths 

 (Hass. pi. 41 ; Greville, Sc. Crypt. Fl. pi. 

 261. fig. 1). Conferva ericetorum, Dillw. 



See Zygnema. 



BiBL. Hassall, I. c. ; Greville, /. c. ; Kiit- 

 zing, Sp. Alg. p. 445, Tab. Phyc. v. pi. 10, 

 &c. ; Eng. Bot. pi. 1553. 



ZYGOSELMIS, Duj.— A genus of Infu- 

 soria, of the family Euglenia. 



Char. Form variable ; movement effected 

 by two similar flagelliform filaments, inces- 

 santly in action. 



Z. nebulosa{F\. 25. fig. 23). Body colour- 

 less, sometimes globular, at others variously 

 expanded so as to become pyriform or top- 

 shaped, turbid from the presence of nume- 

 rous granules. Aquatic; length 1-1100". 



BiBL. Dujardin, Infus. 369. 



