ZYGNEMACE.E. 



[ 828 ] 



ZYGODESMTJS. 



and filled by the globose spore (Hass. I. c. 

 pi. 39. fig. 6 ; Kiitz. I c. v. pi. 11. fig. 4). 



Z. Ealfsii. Filaments 1-1920 to 1-1440" 

 in diameter, joints three or four times as 

 long; transverse processes very much dilated 

 in the middle, containing an elliptical spore, 

 with the long axis at right angles (Hass. 

 I c. pi. 39. figs. 4, 5 ; Kiitz. /. c. v. pi. 11. 

 fig. 2). 



Z. pectinata. Filaments 1-660" in dia- 

 meter, joints equal or a little shorter; cell- 

 contents transversely bipartite, more fre- 

 quently radiato-dentate, pectinate, dull 

 green (Kiitz. /. c. v. pi. 14. fig. 4 ; Eng. Hot. 

 pi. 1611 ?). Possibly this is only a state of 

 Z. cruciata with the spores in the transverse 

 processes ; if so, the subdivision above indi- 

 cated cannot stand. 



BIBL. Hassall, Alga, 160, pis. 38, 39 

 (Tyndartdea) ; Kiitz. (Zygnema and Zygo- 

 gonium, in part), Tab. Phyc. v. pis. 11-17, 

 'Sp. Alg. pp. 444, 445; Kabenh. Alg. iii. 

 248 ; Cooke, Alga, 1882. 



ZYGNEMA'CE^(P1.9.figs. 16-28). A 

 family of Oonfervoid Algse, 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 phenomena 

 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 MOUGKEOTIA). 



The British Genera are : 



Spirogyra. Filaments simple, with the 

 green contents arranged in one or more 

 spiral 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). 



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. 



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. 



Mesocarpus. Filaments simple, with the 

 contents diffused. Conjugation by trans- 

 verse processes, from which the filaments 

 become recurved ; spores in the dilated 

 cross branches. 



Staurocarpus. Filaments simple, with 

 the contents diffused (or rarely in monili- 

 form lines). Conjugation by transverse 

 processes, from which the filaments become 

 recurved ; spores (or sporanges) square or 

 cruciate, in the dilated cross branches. 



Mougeotia. Filaments simple, soon bent 

 at intervals, contents mostly diffused, some- 

 times in several serpentine lines. Conjuga- 

 tion by the inosculation of the filaments at 

 the convexity of the angles; spores not 

 satisfactorily known. 



Thwaitesia, Montagne, resembles Zygnema 

 in its stellate cell-contents ; but the spore 

 formed in one of the parent cells divides 

 into four portions (perhaps not distinct from 

 Zygnema). 



Craterospermum, nearly resembling 

 Staurocarpus and Mougeotia, but with the 

 spore and the short tube in which it is con- 

 tained subconstricted in the middle. 



Pleurocarpus. Simple filaments, with 

 diffused contents, the conjugation taking 

 place between adjacent cells of the same 

 filaments, by means of a short arcuate tube ; 

 spore globose, in the tube. 



Rhynchonema, Kiitzing, has spiral cell- 

 contents like Spirogyra, but conjugates like 

 Pleurocarpus, by an arched tube connecting 

 adjacent cells of the same filament. 



BIBL. Kiitzing, Spec. Alg., Tabul. Phyc. ; 

 Braun, Alg. Unicell. 60 ; Rabenh. Alg. iii. 

 110 ; Cooke, Alga, 1882. 



See also the genera. 



ZYGOC'EROS, Ehr. A genus of Dia- 

 tomacese. Detached frustules of Bn>- 

 DULPHIA ? 



BIBL. Ehrenberg, Abh. Berl. Ak. 1839, 

 131 ; Kiitzing, Bacill 138, and Sp. Alg. 139 ; 

 Eabenh. Alg. i. 310. 



ZYGODAC'TYLA, Brandt. A genus 

 of Campanulinidae (Hydroid Zoophytes). 



Char. Capsules with an operculum formed 

 by many convergent and acuminate seg- 

 ments; polypes cylindrical, tentacles 

 webbed below; reproduction by free me- 

 dusiform gemmae. 



Z. vibrina, Ilfracombe. (Hincks, Brit. 

 Zooph. 191.) 



ZYGODES'MUS, Corda. A genus of 

 Sepedoniei (Hyphomycetous Fungi). Z. 

 fuscus occurs upon bark of fallen branches. 

 Berkeley thinks it possibly may be a form 



