ZOOTHAMNIUM. 



[ 695 ] 



ZYGNEMA. 



ments (PI. 32. figs. 31-4). In the Fucacea? 

 they are minute globular bodies with two 

 cilia (fore and aft) closely resembling some 

 zoospores ; in the Floridese they appear to 

 be globules without cilia ; and those recently 

 described as existing in VAUCHERIA, among 

 the Confervoids, are also biciliated globules 

 with the cilia fore and aft, while those in 

 SPH^EROPLEA resemble the microgonidia of 

 this family, and have then* pair of cilia on 

 the beak. The latter observation is in favour 

 of the microgonidia of Hydrodictyon, &c. 

 being spermatozoids. 



BIBL. Thuret, Ann. des Sc. nat. 3 ser. 

 xiv. p. 214, xvi. p. 5, 4 ser. ii. p. 197, iii. 

 p. 5; A. Braun, Verjungung, fyc., Ray Soc. 

 Vol. 1853, and under the articles above 

 cited. 



ZOOTHAMNIUM, Bory. A genus of 

 Infusoria, of the family Vorticelhna. 



Char. Those of Carchesium, the stalked 

 bodies being of two different kinds. 



According to Stein, the remarks made 

 under OPERCULARIA in regard to the two 

 kinds of bodies, apply equally here, so that 

 the genus is untenable. 



Ehrenberg describes two species, Stein 

 adds two more. 



Z. arbuscula (PL 25. fig. 22). Branches 

 of polypidom racemose-umbellate, bodies 

 white, stalks very thick. Aquatic ; length 

 of polypidora, 1-4" ; of bodies, 1-430". 



BIBL. Ehrenberg, Infus. 288; Stein, 

 Infus. passim. 



ZOSTERA, L. A genus of Monocotyle- 

 donous Flowering Plants (Nat. Ord. Zostera- 

 ceae), growing in sea- water ; remarkable for 

 the POLLEN, of which the grams are repre- 

 sented by tubular filaments destitute of an 

 outer coat and exhibiting ROTATION when 

 fresh. 



ZYGNEMA, Agardh, in part (Tyndaridea, 

 Bory, Hassall). A genus of Zygnemacese 

 (Confervoid Algae), consisting of filamentous 

 plants, with the green contents of the cells 

 arranged in twin, stellate or lobed masses in 

 each joint (fig. 137, page 166). This stellate 

 appearance arises from the presence of ra- 

 diating threads, like those from the nucleus 

 of SPIROGYRA; hence it cannot be well ob- 

 served in dried specimens. Cell-division 

 with previous division of the stellate masses 

 may be well studied in this genus. Kiitzing 

 separates from this genus all the forms in 

 which the spore is formed in the cross branch 

 produced in conjugation, associating them 

 with Zygogonium. We prefer to follow 

 Hassall's distribution of the forms, seeing 



that Zygogonium ericetorum is a plant of very 

 different appearance. If the said character 

 is constant, this genus might be divided into 

 two. 



Spores in one of the parent-cells. 



1. Z. cruciata (fig. 137. p. 166). Fila- 

 ments 1-600" in diameter; joints equal or 

 twice as long ; spores globose (Hassall, 

 L c. infra, pi. 38. fig. 1 ; Kiitz. /. c. infra, 

 v. pi. 17. fig. 4). Z.Dillwynii and stellina 

 of Kiitzing appear to be only smaller states 

 of this ; as also Tynd. lutescens, Hassall, and 

 T. anomala, Ralfs. 



2. Z. stagnalis. Filaments 1-2640" in 

 diameter, joints three or four times as long, 

 spores globose or oblong (Hassall, /. c. 

 pi. 38. figs. 9, 10). Tynd. ovalis, Hass., is 

 perhaps a larger form of this. 



3. Z. insignis. Filaments 1-1800 to 

 1-1560" in diameter, joints twice as long; 

 spores globose (Hass. /. c. pi. 38. figs. 6, 

 7; Kiitz. L c. v. pi. 17- fig. 1). 



4. Z. bicornis. Filaments 1-440 to 1-200" 

 hi diameter, joints twice as long ; spores 

 globose (Hass. 1. c. pi. 38. fig. 5 ; Kiitz. 

 L c. v. pi. 16. fig. 3). 



Spores in the cross branches. 



5. Z. immersa. Filaments 1-1200" in 

 diameter, joints about half as long again ; 

 transverse processes very thick, filled by the 

 large and globose spore (Hass. I. c. pi. 39. 

 fig. 3 ; Kiitz. I. c. v. pi. 12. fig. 5). 



6. Z. conspicua. Filaments 1-1440 to 

 1-1080" in diameter, joints equal or twice as 

 long; transverse processes long, ventricose in 

 the middle, where they enclose the ovate- 



flobose spore (Hass. I. c. pi. 39. figs. 1, 

 ; Kiitz. 1. c. v. pi. 12. fig. 2). 



7. Z. decussata. Filaments 1-1440" in 

 diameter, joints three times (more rarely five 

 times) as long; transverse processes short and 

 filled by the globose spore (Hass. /. c. pi. 

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



8. Z.Ralfsii. Filamentsl-1920tol-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. /. c. pi. 39. figs. 4, 5 ; Kiitz. 

 /. c. v. pi. 11. fig. 2). 



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

 diameter, 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 ; Etig. Bot. pi. 

 1611?). Possibly this is only a state of 



