j. Sterile leaves not much longer than the 

 fertile verticils. N. subglomerata, A. Br. 



8. Sterile leaves much longer than the fertile 



verticils, which are contracted into dense 

 heads. N. glomerulifera, A. Br. 

 * * GLCECARP/E, organs of fructification enveloped in jelly. 



f* JF 



9. Habit diffuse, fruit in spring, membrane of 

 nucleus covered with course granules, N. 

 Capitata (N. ab. E.), Ag. 



10. Habit strict, rigid, fruit in fall, membrane of 

 nucleus delicately reticulated. N. Bastini, 

 Allen. 



11. N. praelonga, A. Br. 



aa. HETEROPHYLLA, verticils composed of dissimilar 

 leaves, some simple, some divided. 



12. N. Clavata, A. Br. 



aa. FLABELLATA. Leaves repeatedly divided. 



13. N. Macounii, Allen. 



NITELLA OPACA, Ag. Syst. Alg. (1824) p. 124. 



N. syncarpa v. opaca A. Br., Flora 1835 ; Kuetzing Phycol. 



germ : Rabenhorst Crypt. Fl. II. p. 195 

 N. syncarpa v. pseudoflexilis A. Br. Flora 1835 : Ganterer 



aust. Char. : Rabenh. Crypt, flora. 

 N. syncarpa v. glomerata A. Br. schweiz. char. : Kuetzing 



sp. Alg. p. 514 

 N. syncarpa v. Smithii, Cosson, Germ. et. Weddell Introduct. 



Fl. de Paris 1842 : Coss. et. Germ. Fl. de Paris, Atlas 



t- 39 

 N. pedunculata Ag. Syst. Alg. 1824 p. xxvii 



N. atrovirens Wallm. Char. 1853 



N. flexilis Smith Engl. Bot. 



N. flexilis v. nidifica, Visiani Fl. Dalm. 



Very variable in >ize, from 5 to 30 cm. in length ; elongated 

 and loosely spreading or abbreviated, and compact according 

 to the depth of water or season of the year. Cell-walls gener- 

 ally firm and somewhat thicker than in N. flexilis, which it re- 

 sembles in habit ; the dried plants darker and less translucent 

 (hence the name, opaca}. Verticils composed of six or seven 

 leaves, which are all once divided into two or three terminals 



