256 JOIIS. BfnK PKTERSKN 



cxaniinaliDii. In sliml, il was Ihc whole planls macrosoopic ap- 

 pearaint', colour, shape, consistence etc. further Ihe dimensions and 

 ramilk-ation ol llii' liireads and Irithomes, llu- ai)pearance ol" Ihe 

 shealhs, and linally if helerocysts or spores should be present, llieir 

 dimensions and general appearance. 



Tilis melhod ol describing Ihe species altains its highesl per- 

 fection in Ho mel and Flahault's "Revision des Noslochacées 

 héléroevslées", and l'or these, the most perlectly developed of the 

 Cijanophficcd'. these features will also, in the main, be suflicient lo 

 characteri/e the species in (juestion in such a manner Ihal Ihey 

 can be determined Nvilh a certain amount of security. 



Gomont, on the contrary, evidently felt this melhod of charac- 

 terizalion to be insufficienl as lo species belonging to the Oscillarieæ 

 and therefore attempted to find new distinguishing characters. He 

 inlroduced t\vo new methods Nvhereby to dislinguish Ihe species, 

 viz. by taking special nole of 1) Ihe apex of Ihe trichome, wilh 

 regard to its shape, especially as to whether il had a calyplra or 

 nol; 2) the reaction of chlor-zinc-iodine on the shealhs. The im- 

 portance of the former character was, lo begin with, dispuled in 

 various (juarters, bul novv cerlainly all will agree Ihal Ihe distin- 

 guishing characters derived from Ihe appearance of Ihe apex has 

 proved an added security in the characterization of the species. 



Among the Oscillarieæ Gomonl (18*S«, p. 220 II) found Ihal 

 Ihe micro-chemical relations of the shealhs diflered in Ihe various 

 species, not only Nvithin Ihe greal generic groups, bul also within 

 Ihe individual genera. Therefore in his "Monographie des Oscil- 

 lariées" he uses Ihe reaction of chlor-zinc-iodine on Ihe shealhs as 

 a dislinclive character of Ihe species. Within this group a cutiniza- 

 lion of the shealhs seldoni occurs, therefore he, in Ihe main, only 

 needs lo consider 2 cases: — 1) whelher Ihe sheath becomes blue 

 when trealed with chlor-zinc-iodine or 2) ^vhelhcr il remains un- 

 slained. 



Also this distinguishing character appears lo be an accpiisilion 

 to systemalism, i)ul a Iheorelical basis for its application is still 

 lacking, and this can hardly be obtained excepl by means of pure 

 cuilnrcs. A guaranlee is slill wanling as lo whelher or nol Ihe re- 

 action of chlor-zinc-iodine on the shealhs can vary during the de- 

 veloj)menl of the individual plant. I have reason to presume Ihal 

 Ihis is the case with fhifxitosiphon laminosns. wherc Ihe gelatinous 

 shealhs Ihat envelop f. aiuilxvnoiiJcs do nol colour with chlor-zinc- 



