68 FRESH-WATER ALG^ OP THE UNITED STATES. 



These plants grow in the majority of cases in the air, in such situation as on 

 the face of dripping rocks,- on the trunks and branches of trees, on moist ground, 

 &c. ; but some of the species are found in the water, either attached or floating. 

 They generally form little mats of indefinite extent, but occasionally the filaments 

 are united more closely into an almost membranaceous stratum. 



The species are, I think, in most instances readily distinguished, the characters 

 being partly discoverable with the unaided eye and partly microscopic. The 

 points to be attended to in the first category are the size, color, form, and 

 consistency of the mats of fronds, and the place of growth. In the second are 

 included the general shape of the frond and its size and method of branching ; 

 the general shape, color, and size of the cells, the thickness of their walls and the 

 method of their arrangement, both in the main thallus and the branches, also the 

 form, &c., of the end cells of the branches; the heterocysts, their absence, or, if 

 present, their frequency, size, shape, color, and position j , the sheaths, their color 

 and firmness, and the character of their surface. 



Genus SIEOSIPHON, Ktz. 



Trichotnata torulosa, vaginata, plerumque ramossissima et aureo- vel olivaceo-fusca, e cellulis 

 pachydermaticis 1-2-3 vel pluri-seriatis formata et cellulis interstitialibus (saspe nullis) subglobosis 

 vel oblongis coloratis instructa. Vagina plerumque crassissima, firma, pulchre aureo-fusca, lutea 

 vel olivacea, in apicem obtusum plus minus attenuata. 



Filament torulose, sheathed, mostly very much branched, yellowish, or olivaceous-fuscous, formed 

 of thick-walled 1-2-3 or many seriate cells and furnished with interstitial cells (often wanting) 

 which are globose or oblong and colored. Sheaths mostly very thick, firm, beautiful golden fus- 

 cous, clay-colored or olivaceous, more or less attenuate at the obtuse apex. 



a. Gellula in trichomatibus plerumque in serie simplice vel duplici ordinata. 



a. Cells mostly arranged in a simple or double series in the filament. 



S. scytenematoides, Wood. 



S. strato submembranaceo, nigro-viride, saepe interrupto, cum superficie insequale ; trichoma- 

 tibus SKpe arete intricatis, flexuosis aut varie curvatis, haud rigidis, plerumque vix ramosis ; 

 cellulis uniseriatis, interdum interrnptis, arctis, irregulare quadrangulis, diametro subaequa- 

 libus aut 1-3 plo brevioribus, haud distincte granulatis, cteruleo-viridibus; vaginis amplis, 

 haud distincte lamellosis, supej-ficie enormiter corrugatis et hirtis, plerumque coloris experti- 

 bus sed interdum dilute brunneis. 



2)iam.— Sine vag. max. y/^/ = .00066" ; cum vag. max. ^l^^" = 0013". 



Syn. — "S. scytenematoides, Wood, Prodromus, Proc. Amer. Philos. Soc, 1869, p. 134. 



Hab. — South Carolina. (Ravenel.) 



S. In a subraembranaceous, blackish-green, frequently interrupted stratum, with an uneven 

 surface ; filaments often closely intricate, flexuous or variously curved, not rigid, mostly 

 sparsely branched ; cells uni-seriate, sometimes interrupted, close, irregularly quadrangular, 

 about equal in length to their diameter, or about 1-3 times shorter, not distinctly granulate, 

 bluish-green; sheaths ample, not distinctly lamellate, their surface rough and corrugate, 

 transparent, mostly colorless, sometimes light-brown. 



Remarks. — This species was collected in South Carolina by Prof. Eavenel, who 

 found it in the month of February growing on the limbs of Myrica cerifera. The 



