270 FRESH-WATER ALGJE OF THE UNITED STATES. 



a number of generations ; finally the young forms commence 

 to develop as represented by figs. 11-14. 



Another process differing somewhat in the details may be 

 illustrated. By the difflueiice of the walls of the filaments 

 and of the membranes of the internal cells, the niicrogo- 

 nidia are scattered ; from these large masses of small, almost 

 colorless, thin meinbraued, circular cells are evolved (figs. 

 15, 16); gradually a nucleus is formed in them (fig. 17.); 

 they enlarge, the nucleus divides, producing larger and 

 more firmly constructed cells (fig. 18), which become en- 

 cysted by lamellate membranes, dividing and redividing and 

 enlarging (figs. 19, 20), resulting in cells of the true Gloeo- 

 copsa-type. These cells often occur in such quantities on 

 wet cliffs, that they may be stripped with the palm of the 

 hand. Among them there are always some in an early 

 state of development, others more advanced and some fully 

 grown. Most of the cells are sterile. 



Plate CXCV, fig. 16, fragments of specimen of the same 

 species, from wet rocks, Black Water Creek, West Virginia. 

 Reddish brown with three bright aeruginous spots, indi- 

 cating preliminaries for fresh growth. Associated with 

 forms of this kind are young aeruginous filaments, 9-12 /* 

 diameter, others yellowish 25-30 yw and the larger forms 

 38-62 yu ; fig. 15, a tuberculose specimen, however merely a 

 form of 8. pulvinaim, which occurs occasionally in older 

 masses. Kirchner denominates this form 8. mamittosum, and 

 credits the species to Agardh; but Agardh's plant was, 

 probably, no true Sirosiphon, but a Stigonema, a Lichen ; 

 nevertheless we retain the name and call it 



Forma mamillosum. It is not identical with Agardh's form. 



SlROSIPHON CORALLOIDES, Kg. 



Strata more or less expanded, tomentose, greenish-black 

 or fuliginous black, trichonies rather short, prostrate, rigid, 

 sometimes very irregular in outline, much branched, tuber- 

 culose, yellowish brown or greenish ; branches erect, poly- 

 morphic, often short, sometimes papilliform, obtuse; two 

 to eight or more series of internal cells ; cells round or sub- 

 quadrangular, aeruginous green, granular ; sheath often 

 yellowish brown or golden yellow. 



Diameter of filaments from 25-150 /*. 



The finest specimens are from stones along the rocky 

 shores of Green Pond, New Jersey, constantly washed by 



