NITBLLA MUCBONATA. 117 



extra-British plant, N. virgata Wallm., also considered by 

 Braun as a subspecies or variety, is very long and slender, 

 having the sterile branchlets often 3 times forked, and having 

 geminate oogonia. 



N. traiislucens and N. mucronata, so widely different in 

 other respects, possess a close similarity in the decoration of 

 their membranes. They, with N. tenuissima in its earlier 

 stages, are the only British species which show a reticulated 

 pattern. In N. tenuissima this pattern soon assumes a different 

 and a distinctive form, but with N. translucens and N. mucro- 

 nata it remains unchanged; the only apparent distinction 

 between the two being in 'the size of the furrows, which 

 measure, according to Nordstedt, in N. translucens 3-5 /z in 

 diameter, and in N. mucronata 4-6 fi in diameter. 



Var. b. gracillima. 



Groves & Bxtllock-Webstbe, in Joum. Bot. LV, p. 324 (1917). 

 (Plate I, mucli enlarged.) 



8te7n and hrmichlets usually slender. Ultimate ray 

 often 3-celled ; penultimate cell tapering gradually to 

 the apex, so that the apex is not much broader than 

 the base of the apical cell. Oospore c. 290 /x long, 

 275 /Lt broad. 



Gloucestershire, "W., small pond, near Wickwar 

 {Miss Ida M. Roper, 1917). 



7. Nitella gracilis Agardh. 

 (Plate XIII.) 



Chara gracilis Smith Engl. Bot. 2140 (1810). 



Betjzelitjs OIds. Char. p. 24 (1824). 



Rbichbnbach Iconogr. f. 1069 (1830). 



Brattn in Ann. Sc. Nat. ser. 2, 1, p. 351 (1834) ; in Flora, XVIII, i, 

 p. S3 (1835). 



Gantbebr OsteiT. Char. p. 10, t. 1, f. 2 (1847). 



Babington in Ann. & Mag. Nat. Hist. ser. 2, V, p. 84 (1850). 

 CfleadUs var. gracilis S. F. Gray, Nat. Arr. Brit. PL II, p. 28 (1821). 

 C. exilis 'BarHeri' Amici in Mem. Accad. Modena, I, p. 216, t. 3, f. 6-7 

 (1827). 



