DESMIDIACE.E. 



[ 245 ] 



DESmDIACEiE. 



Dr.vTOMACE-s:. Their preservation is a 

 difficult matter, as almost all the preser- 

 vative liquids alter them more or less. 

 Those producing the smallest amount of 

 change are Thwaites's liquid, Ralf s's liquid, 

 or simple camphor-water : but these liquids 

 always escape in time from the cells. A 

 few, for example Pediastrum,Kve unchanged 

 by concentrated solution of chloride of cal- 

 cium very gradually added, except that the 

 colour becomes rather paler, or solution of 

 acetate of potash ; moreover the cell-mem- 

 brane, upon the forms of which the 

 characters mainly depend, remains unal- 

 tered in all the kinds when kept in these 

 solutions. Many prefer glycerine, which is 

 really the best preservative medium ; in 

 some cases glycerine-jelly is used. 

 See Preservation. 



Analysis of the Tribes and Genera. (PI. 14.) 



I. CLOSTERiE-tE. Cells single, elongated, 

 never spinous, freqiiently not constricted 

 in the middle (sporangia smooth). 

 Closterimn. Cell crescent-shaped or arcu- 

 ate, or much attenuated at the ends, not con- 

 stricted in the middle (figs. 40-45, 57, 58). 



Penium. Cell straight, not or very 

 slightly constricted in the middle, rounded 

 at the ends (fig. 36). 



Tetmemorus, Cell straight, constricted 

 i the middle, notched at the ends (figs. 33, 

 34). 



Docidium. Cell straight, constricted in 

 the middle, truncate at the ends (figs. 38, 39). 



Spirotmiia. Cell straight, not constricted j 

 endochrome spiral (fig. 59). 



II. CosMARiEiE. Cells single, distinctly 

 constricted in the middle ; segments sel- 

 dom longer than broad (sporangia spinous 

 or tuberculated). 



Micrasterias. Lobes of the segments in- 

 cised or bidentate (fig. 13). 



Euastrum. Segments sinuated, generally 

 notched at the ends, and with inflated pro- 

 tuberances (figs. 14 to 17). 



Cosmarium. Segments neither notched 

 nor sinuated, end view elliptic, circular, or 

 cruciform (figs. 18 to 22). 



Xanfhidium. Segments compressed, 

 entire, spinous (figs. 23 to 25). 



Arthrodesmus. Segments compressed, 

 each with only two spines (fig. 27). 



Staurastrum. End view angular, radiate, 

 or with elongated processes (figs. 26, 28-32, 

 and 56). 



m, Desmidie^e. Cells united into an 



elongated jointed filament (sporangia 



spherical, smooth). 



Geniculai-ia. Filament cylindrlcal,smooth ; 

 endochrome spiral (PI. 51. fig. .36). 



Gonatozijgon. Filament cylindrical or 

 fusiform, smooth ; endochrome longitudinal, 

 wavy (PI. 51. fig. 37). 



Hyalotheca. Filament cylindrical, ceUs 

 crenate (PI. 14. figs. 1, 2). 



Didymoprium. Filament cylindi'ical or 

 subcylindrical ; cells with two opposite bi- 

 dentate projections (figs. 5, 6). 



Desmidium. Filament triangular or qua- 

 drangular ; cells with two opposite bidentate 

 projections (figs. 7, 8), 



Aptogonum. Filament triangular or plane, 

 with foramina between the joints (figs. 52, 

 55). 



Sphisrozosma. Filament plane, margins 

 deeply incised or sinuated (figs. 9, 10). 



IV. Ajstkistrodesiil^. Cells elongated, en- 

 tire, small, gTouped in faggot-like bimdles. 

 AnJcisirodesmus (fig. 47). 



V. Pediastre^. Cells grouped in the 

 form of a disk or star, or placed side by 

 side in one or two short rows. 

 Pedtastrmn. CeUs forming a disk or star, 



marginal cells bidentate (fig. 48). 



Monactiyius, Cells as in Pediastrum, but 

 margbial cells uuidentate (PI. 36. fig. 28). 



Scenedesmiis. Cells placed side by side 

 in one or two rows (figs. 50, 51, 53, 54). 



Ccelastrtim. Cells forming a hollow sphere 

 (PI. 3. fig. 8). 



Three interesting genera are described 

 and figiu-ed by Wallich from Lower Ben- 

 gal {Leuronema, Onychonejna, and Strep- 

 tonema). 



Tetrachastrum, AxQh.e:\=Micrasterias,^i. ; 

 Triploceras= Docidium, pt. ; Lejitoajstine^na, 

 Arch.= Gonatozygo7i, De Bary; Spondylo- 

 siuin= Splicer ozosma, pt. 



Eabenhorst places Cosmocladium among 

 the Palmellacefe. 



BiBL. Ralfs, Br. Desmid, ; Ehrenberg, 

 Inf. ; Pritchard, Infus. ; Hassall, Ah/ce ; 

 Nageli, Einzell. Alg. 1849 ; Braim, Verjiing. 

 {Ray Soc. 1853); Focke, Phijs. Studien, 

 1848 ; Caspary, Bot. Zeit. viii. 786, 1850 ; 

 Pringsheim, Flora^\S&'2, 486 ; Hofmeister, 

 Ann. N. H. 3 ser. i. 1 ; Carter, ibid. 2 ser. 

 xvii. ; Thomas, Mir. Tr. 3 ser. ; Bailey 

 Smiths. C'ontr. 1854; Rabenhorst, Fl. Alg. 

 iii. 102 ; WaUich, Ann. N. H. 1860, v. 184, 

 273; Archer, Qu. M. Jn. 1860, viii. 85, 

 215, 235 ; Brebisson, Liste, 1856, 2 plates ; 



