68 FRESn-WATER A L G .E OF THE UNITED STATES. 



These plants grow in the majority of cases in the air, in snch 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 o-enerally 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. Sec, of the end cells of the branches; the hotorocysts, their absence, or, if 

 present, tlieir frequency, size, shape, color, and position; the sheaths, their color 

 and firmness, and the character of their surface. 



Genus SIROSIPHON, Ktz. 



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

 pachydermaticis 1-2-3 vel pluri-seriatis foniiata et celliilis iuterstitialibtis (siepe nullis) suljglobosis 

 vel oblongis coloratis iiistriicta. Vagina plerumque crassissima, firuia, pulcbre aureo-fusea, lutea 

 vel olivaeea, in apicem obtusuui 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. Cellula in trichomalibus plerumque in serie simplice vel duplici ordinaia. 



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



S. scytenematoides, Wood. 



S. strato submembranaceo, nigro-viride, sispe interrupto, cum superficie inoequale ; trichoma- 

 libus soepe arete intricatis, flexuosis aut varie curvatis, baud rigidis, plerumque vis ramosis ; 

 cellulis uniscriatis, interdum interruptis, arctis, irregulare quadrangulis, diametro sub»qua- 

 libus aut 1-3 plo brevioriljus, baud distincte granulatis, cteruleo-viridibus; vaginis amplis, 

 baud distincte lamellosis, superficie enormiter corrugatis et hirtis, plerumque coloris experti- 

 bus sed interdum dilute brunneis. 



Diam.— Sine vag. max. jg%^" = .000(36" ; cum vag. max. ^ig^" = .0013". 



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



Eab. — South Carolina. (Ravenel.) 



S. In a submembranaceous, 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, 

 blui.sh-green; sheaths ample, not distinctly lamellate, their surface rough and corrugate, 

 transparent, mostly colorless, sometimes light-brown. 



Bemarks.— This species was collected in South Carolina by Prof. Ravenel, who 

 found it in the month of February growing on the limbs of Mi/r!ca eeri/era. The 



