FRESH-WATER ALG^ OF THE UNITED STATES. 55 



Light bluish-green, or olivaceous-green, apex in the mature filament prolonged into a long, 

 distinctly articulated hyaline seta ; sheath transparent — in the immature filament distally, 

 broad, and distinct although hyaline, below rather thick and close ; in the mature filament 

 below close, indistinct, above dissolved in fibrillae and wanting at the apex; heterocysts 

 globose, sometimes geminate. 



Bemarhs. — This plant was found growing with other low algse in a thick jelly, 

 which clothed some wet, dripping rocks near Manayunk. Tn the young filaments 

 the sheath is produced above into a broad, thick, gelatinous-looking portion, the 

 cavity of which is often scarcely apparent. The cytioplasm in such filaments is 

 mostly of a light bluish-green color, is granular and not very apparent. In older 

 filaments, the trichoma above is prolonged into a long, curved hyaline point, and the 

 sheath just below the base of this- is split into a number of fibrillse. No spores 

 were perceived. The increase of the species appears to take place in the follow- 

 ing manner: Near the middle of the filament a tumid swelling forms, in the 

 centre of which appears after awhile a constriction, and this increases uiitil at last 

 there are shaped out the bases of two filaments. Then the heterocysts appear, and 

 finally the two halves of the original trichoma separate — each a perfect filament. 

 (Eig. 3, pi. 5.) Sometimes, instead of a pair of filaments being thus formed, but 

 a single base is shaped out at the place of swelling, and the original filaments split, 

 as it were, thus giving origin to a second trichoma, which for awhile appears . as a 

 branch of the former, but is soon detached from it. In some specimens there are 

 two heterocysts, unless the proximal of these, which is a light orange-clay color, 

 represents a spore. 



Fig. 3, pi. 5, represents different forms of this species. 



Family SCYTONEMAOE^. 



Trichomata articulata, ssepe moniliformia vel submoniliformia, vaginata, pseudoramosa, cellulis 

 limataneis, ad pseudoramulorum basin, vel interstitialibus, plerumque pachydermaticis instructa. 

 Vaginae e stratis pluribus (etsi non semper distinctis) formitse, superficie Iseves, corrugatoe vel 

 exasperatse, crustatae, nonumquam stratis exterioribus in fibrillas discedentibus, hand raro passim 

 intumescentes vel ocreatse. 



Vegetatio non terminalis ; cellularum vegetativarum divisio ad unam directionem, initio in trieho- 

 raatibus medio, postea in utroque fine saepe alternans. Cellulse limitanese ad utrumque polum locello 

 lueido instructae. 



Propagatio gonidiis plerumque exultima generatione ortis. Gonidia plerumque numerosa seriata 

 e vagina se exserunt tumque in singula secedunt. (R.) 



Filaments equal, articulate, often moniliform or submoniliform, vaginate, pseudoramosa, furnished 

 with heterocysts which are either interstitial or at the base of the branches, and are mostly thick- 

 walled. Sheaths formed of numerous strata (not always distinct), their surface smooth, corrugate, 

 or roughened, the exterior stratum sometimes breaking up into fibrillse, not rarely intumescent or 

 ochreate. 



Vegetation not terminal ; division of the cells occurring in one direction, in the beginning in the 

 middle of the trichoma, afterwards often alternately at each end. Heterocysts furnished with a trans- 

 lucent spot at each end. 



Propagation mostly by gonidia arising from the last generation Gonidia mostly numerously 

 seriate, passing out of the sheaths and then separating one from the other. 



