268 FRESH-WATER ALG^ OF THE UNITED STATES. 







produce various forms of cells heretofore known as Microcystis, 

 Gloeocapsa, Gloeothece, etc. After passing through, often numer- 

 ous cycles of evolution, the original form is reproduced. 



The propriety of Cooke's remark, in his British Fresh-water 

 Algol, p. 270, "It can scarcely be doubted that all the members 

 of the genus Stigonema (or Sirosiphon) and Hapalosiphon must be 

 transfered to the Lichens," is beyond our comprehension. 



The generic terms Stigonema, Ag., and Sirosiphon, Kg., are 

 sometimes interchanged, as though both represented the same 

 kind of plants ; this does not appear to be the case. The true 

 Stigonema-forms, according to Agardh himself, who originally 

 suggested the name, partake of the nature of Lichens. He says 

 in his Sys. Algarum, page xxii, ' i Habitus magis Lichenosus. ' ; Eaben- 

 horst also says of Stigonema, l i Genus ad Lichenes eerie referendum, 

 in aliis apothecia detecta sunt," etc. But Stigonema-forhis are not 

 related to Sirosiphon-forms, hence Kuetzing deemed it wise to 

 separate the two, and made the newer genus Sirosiphon. If the 

 two represented similar plants, then the term Stigonema, 1824, 

 would have the priority claim. Kuetzing' s term dates only to 

 1843, but his diagnosis describes the forms here to be presented ; 

 Agardh' s description falls short. 



Hapalosiphon also rests on a good basis among the Algae. 

 A study of the life-history of Sirosiphon, briefly illustrated in 

 this work, will confirm the correctness of the position asserted. 



SIROSIPHON PTJLVINATUS, Breb. 



Forming expanded strata on dripping rocks ; deep olive- 

 black, cushion-like, or sometimes velvet-like when dry; 

 masses about two lines thick (4 mm). Filaments often very 

 thick, much branched, brownish, irregularly curved; 

 branches polymorphous, varying in thickness and length 

 according to age, obtusely rounded at the apex ; cells of the 

 filaments very variable, younger forms with a single series, 

 and older forms from two to three to many series. Sheaths 

 thick, yellow-fuscous to deep fuscous, pellucid or opaque, 

 sometimes rugose-tuberculate. 



Diameter of filaments range from 10-12 fa for younger 

 plants ; up to 100 fa for older ones. 



This is our most common form, often spreading over drip- 

 ping rocks in partially shaded mountain ravines, many 

 square yards in extent. The plants are not attached except 

 by a mucus in which all are more or less imbedded. Young 

 and older filaments, with one, two, or more series of cells, 

 and macrogonidia (Gloeocapsa cells) are intermingled; fila- 



