FRESn-WATER ALG^ OF THE UXITED STATES. 187 



escaped into the water, through the cell wall. Each cell in this way gave origin 

 to a single zoospore. The walls did not melt away in the water, and, as a nunihcr 

 of consecutive cells underwent these changes at the same time, the filament or a 

 portion of it was left as an empty shell. The zoospores were of the usual shape, 

 with a bright anterior spot or beak. The number of cilia was not noted. After 

 a time they settled down generally in clusters, attaching themselves to some fort-ign 

 particle, dropping their cilia and acquiring a cellulose wall. (Fig. 7e, pi. 18.) They 

 then elongated, underwent the ordinary cell division in a transverse direction, and, 

 by the repetition of this, gradually grew into filaments similar to that from which 

 they sprang. 



Fig. 7 (7, pi 18, represents a young filament just formed in this manner, magni- 

 fied 500 diameters. 



Genus CLADOPHORA, Ktz. (1843.) 



Fila cc'Uularum scrie siinplici formata, varie ramosa. Rami filo central! similes. Cytioderma 

 pioruinque crassum, laiuellosiini. Cytioplasma parietalc. 



Filaments composed of a simple series of cells and variously branched. Cytioderm mostly thick 

 and lamellate. Cytioplasm parietal. 



Eemarhs. — The Cladophora are branched plants of rather rigid habits, which 

 grow both in salt and fresh water. They are readily recognizable by their 

 comparatively still appearance, the absence of gelatinous matter about them, and 

 by the want of regularity in their branching. A large number of species have 

 been described, most of which are marine. They are exceedingly difficult to define, 

 and it is very possible that their hitherto undiscovered sexual reproduction maybe 

 finally found to afford the only true characters. I have identified two European 

 forms as growing near this city, and a third has been recognized by Prof. Harvey, 

 as found in our northern States. 



I have never seen the production of zoospores in this family, but they are said 

 to be formed by the simultaneous division of the layer of chlorophyllous proto- 

 plasm, which fills the outer part of the cell cavity. They exhibit the power of 

 very active motion even before their exit from the cell, which occurs through a 

 papilloid orifice, mostly at the end of the cell, sometimes in its side. Their cilia 

 are sometimes two, sometimes four in number, and their life-history appears to be 

 precisely similar to that of other zoospores. 



CI. g^lonierata, (Linn.) 



Raniuli fili primarii in parte siiperiore atque ramorum ordinis secnndi et tertii plerumqne 

 fasciculato- vel penicilliformi-aggregati. CelliiliB niaxima3 vegetse cytioplasmate cellularuni 

 parieti retiformi- vel subspiraliter applicato. CeliuLe fructiferoe semper termiualcs, inforiores 

 semper steriles videntur. (R.) 



Syn. — CI. glomcrata, (KtJTZiNG) Rabenhorst, Flora Europ. Algarum, Sect. III. p. 33T. 



Hah. — Lake Ontario; Pickering. Falhs of Niagara; Lakes Erie, Iluron, and Michigan; 

 Fourth Lake, near Madison, Wisconsin ; Bailey. 



" Filaments tufted, bushy, somewhat rigid, much branched, bright grass-green ; branches 

 crowded, irregular, erecto-patent, repeatedly divided ; ultimate ramuli sccund, subfasciculate ; 



articulations 4-S time.'; as long as broad." 



