82 FRESII-WATER A L G J3 OF THE U iNI T E D STATES. 



No opportunity was afforded to study the development of this plant; but there 

 can be but little doubt that the globular, thickish-walled cells are finally dis- 

 charged by a rupture of the membrane and escape from the softening jelly into the 

 water, eacli to be a possible starting point for a new frond. 



1 have given this curious plant the name of Pagerogcda, from its milky white- 

 ness. Floating in the water it offered so close a resemblance to the spawn of frogs, 

 though more opaque, that my companion, a most excellent naturalist, insisted, 

 until its true nature Avas absolutely demonstrated, that I was simply wasting my 

 time collecting the spawn of an amphibian. 



P. stellio, Csp- nov. ) 



Diam. — Froud ^ incb ; cells jt^so" — 5TsViy"- 



Genus TETRASPORA, Link. 



Thallus gdatinosus, membranaceus vel subraembranacens, initio saccato-clausns, state prorectiori 

 vel postea esplanatus. Cellulffi globosse (vel anguloso-rotundatae) pins minus distantes sed in familias 

 magnas unistratas consociatfe ; tegumentis crassis in mucum homogenenm cito diffluentibus. Cel- 

 lularum divisio in planitiei duas directiones alteruans. 



Propagatio fit gonidiis mobilibus. 



Thallus gelatinous, membranous or submerabranons, in the beginning a short sack, afterward 

 expanded. Cells globose, or angularly so, more or less distant but consociated in a single stratum 

 into large families. Tegument thick, very rapidly difiluent into a homogeneous mucus. Division 

 occurring in two directions in the one plane. 



Propagation by means of zoospores. 



T. lubrica ? (Roth) Aa. 



T. thallo gelatinoso-membranaceo, lubrico, dilutissime viride, tubuloso sed ssepe postea explanato, 

 siraplice vel ramoso, undulato-sinuoso, SKpe laeunis munerosis perforate ; cellulis globosis 

 vel clliiiticis, Iste viridibus, interdum singulis sed plerumque quaternis vel gemiiiis, locello 

 achroo hyalino parietali s«pe prseditis ; cytiodermate tenuissimo, baud distincte visibile. 



Dinm.—QcW. ^^Vir"— ttjV/ = 0.00025"— 0.0005". 



Syn. — T perforata, Harvey. Bailey, Silliman's Journal, N. S. vol. iii. 



T. lubrica, (Roth) Ag. Rabenhoest, Flora Europ. Algarum, Sect III. p. 41. 



Hab. — Northern Atlantic States. 



Thallus gelatinoso-membranaceous, slippery, very dilute green^ tubular, but often finally ex- 

 panded, simple or branched, undulately-sinuate, often perforated with numerous holes ; cells 

 globose or elliptical, bright green, sometimes single but mostly in pairs or fours, furnished 

 with a parietal transparent hyaline space; cytioderm very thin, not distinctly visible. 



Remarlcs. — This little plant is very common around this city, growing usually 

 in limpid, quiet water, such as springs, little rushy pools, and clean ditches. The 

 frond is a translucent, light green or scarcely greenish, very slippery jelly, with 

 the edges often very markedly undulate. It is very rarely simple, but on the con- 

 trary is often very much and very irregularly branched, frequently indeed consist- 

 ing of several broad portions united by narrow necks. It is an irregular sack, 

 generally profusely perforate, and often with large imperfect portions. " I think it 

 finally in many instances becomes expanded and open. It is sometimes found 

 lying'on the bottom, but more frequently floats on the surface of the water. The 

 breadth of the frond varies from two or three lines to an inch. The length often 

 reaches several inches. The cells are mostly globular ; but, immediately after 



