156 Chlorophycece 



apices of the cells are generally rounded or truncately rounded. 

 There is a single axile, substellate chloroplast in each semicell and 

 in the centre of each chloroplast is a large pyrenoid. The radiating 

 prolongations of the chloroplast vary in number in the different 

 species, and often become flattened against the interior of the 

 cell-wall. 



The most abundant species is Cyl. Brebissonii Menegh. (length 43 55 p. ; 

 breadth 15 18 p., fig. 54 H and I) which occurs in quantity in upland 

 Sphagnum-bogs and in peaty pools. It sometimes occurs in pure masses both 

 amongst Sphagnum and on wet peat. Cyl. crassa De Bary also occurs in 

 Sphagnum-bogs and amongst other Algae and mosses on wet rocks. Cyl. 

 diplospora Lund, prefers the waters of lakes and quiet pools, and is a much 

 rarer plant ; one form of it var. major West is the largest member of the 

 genus; length 102 114 p.; breadth 48 54 p.. 



Genus Netriuxn (Nag., 1849). A genus with straight, cylin- 

 drical, oblong-cylindrical or fusiform cells, and without any median 

 constriction. The chloroplasts are two (in one species four) in 

 number, one (in one species two) in each semicell ; each chloro- 

 plast is axile with about six radiating longitudinal plates. These 

 plates are deeply notched along their free edges in all except 

 Netrium inter -r -upturn. There are several pyrenoids in each chloro- 

 plast, generally small and scattered. The plants placed in this 

 genus are excluded from the Placoderm Desmids, and therefore 

 from the genus Penium, on account of the structure of their cell- 

 wall, which is unsegmented, without pores, destitute of a differen- 

 tiated outer layer, and quite smooth. 



N. Digitus (Ehrenb.) Itzigsh. & Rothe is one of the most abundant 

 Desmids of elevated boggy moorlands and varies much in form and size; 

 length 130 387 /a; breadth 40 82 p.; fig. 54 K. N. oblongum (De Bary) 

 Liitkem. occurs in similar situations but is not quite so frequent ; length 

 96 135 p. ; breadth 32 33 p.. JV. interruptum (Breb.) Liitkem. is cylindrical 

 with obtusely conical apices, and each chloroplast is transversely segmented, 

 so that there are four chloroplasts in each cell arranged in an axile series. In 

 this species the free edges of the plates are not notched ; length 220 320 p. ; 

 breadth 37 64 /n. 



Sub-family II. PLACODEKM.E. 



This group includes the great majority of Desmids and is 

 characterized by the segmented cell-wall with its differentiated 

 outer layer. The cell-wall usually possesses pores, but this is not 

 invariably the case. There is always a very distinct line of demarca- 

 tion between the old and new semicells, the younger portions of 



