256 FRESH-WATER ALGLE OF THE UNITED STATED. 



ing also secondary branchlets in the same manner. Hetero- 

 cysts more or less compressed globose, yellow. 

 Diameter of filaments, including sheath, 12-16 /*. 

 From the bark of Cypress trees, Florida. 



In a short paper to the Bulletin of the Torrey Botanical 

 Club, New York, April, 1878, a Nostoc was represented as 

 the Matrix of Scytonema. The present plant was taken as 

 one of the illustrations ; it is very distinct in the character 

 of the psewdo-branchlets and hence well suited to trace the 

 various stages of development. 



Plate CLXXXVII, figs. 1, 2, 3, parts of three filaments 

 with characteristic branchlets, heterocysts, and arrangement 

 of internal filaments ; fig. 4, the microgonidia developed 

 from the cells of the filaments, the same gradually enlarg- 

 ing; fig. 5, forming large cysts, (sporangia), the Microcystis 

 forms ; these divide forming smaller cysts ; fig. 6, within the 

 maternal tegument (Gloeocapsa-foTyns), or the microgonidia 

 arrange themselves in series, JVbstoc-like (figs. 7, 8, 9); these 

 uioniliform series gradually become surrounded with a gela- 

 tinous envelope, at first very thin, then more consistent 

 until a membrane is formed ; fig. 10, sometimes wide, then 

 close. The tegument is finally dissolved and the vermiform 

 contents are set free ; figs. 11-15, a few varieties of such, in 

 part showing a tendency to double branchlets ; figs. 16, 17, 

 withered branchlets. 



SCYTONEMA CORTEX, Wood. 



Forming small turfy spots of an olive green or brown 

 color on the bark of trees ; filaments mostly creeping, rather 

 sparsely, twin or singly branched. Internal trichome arti- 

 culate, joints longer or shorter than broad ; after division 

 one-half diameter; sheaths close, rather thin, transparent, 

 colorless or sometimes light brown ; heterocysts subglobular, 

 or quadrate, usually single, interstitial sometimes at the 

 base of branchlets. Diameter of filaments variable ; smaller 

 forms, 8-10 /* ; larger forms, up to 15 p. 



Syn. Scytonema Ravenelii, Wood. --Very near also to Scytonema 

 truncicola, Rab. 



Among no less than thirty different specimens collected 

 by H. W. Ravenel in South Carolina, and by J. D. Smith in 

 Florida, from the trunks of various kinds of trees, I found 

 this plant in almost as many forms and phases of growth. 

 The number afforded ample opportunity for a thorough 

 study. Its development from macrospores was well exem- 



