NEW MYXOPHYCEAE FROM PORTO RICO 



73 



Growiag; on rocks h. -^^it ten miles north of Utiiado, no. 1537 a, 

 type. . 



Scytonema capitatmn Jiao one character not previonsly re- 

 ported in any other species of the genus : viz., the thickening of 

 the apex of the filament. This is apparently not uniform in all 

 of the filaments, but occurs under certain conditions in the same 

 way that the capitate Homocysteae occur, typical capitate apices 

 often being difficult to find in a collection of a species which 

 under certain conditions may have them in abundance. The 

 trichomes at times seem to grow very rapidly, extending far 

 beyond the sheath. A sheath is then secreted, and it appears as 

 though the apical cell secretes much more than the cells farther 

 back in the triehome. The cap is frequently as much as eight or 

 ten microns thick, whereas the sheaths are from two to four 

 microns thick. AVhen in rapid division the cells in the meriste- 

 matic region are often not over two and a half microns thick, and 

 in the older i^arts of the triehome quadrate cells may be found. 



Scytonema longiarticulatum sp. nov. 



Plate 15, figure 28 



Filaments associated with other algae, not forming a definite 

 stratum alone, 400-500 |j long, 15-18 i_i diam., arcuate or almost 

 straight ; trichomes not constricted at the dissepiments, 9-11 m 

 diam. at the apices, 5-8 m diam. in the body of the filament; cells 

 olive-green, finely granular, 18-25 m (up to 35 m) long in the body 

 of the filament ; heterocysts cylindrical, of the same size as the 

 cells, sparse; sheath at first completely hyaline, finally becoming- 

 brown in contact with the triehome, the thick surface layer re- 

 maining hyaline for considerable length of time but finally the 

 whole sheath becoming dark brown, homogeneous or faintly 

 lamellose at maturity, the lamellae not diverging. 



Growing in association with other species of Myxophyceae 

 on pulverized rock at "Campo," Maricao, no. 1229 a, type; on 

 rock at Jayuya, no. 1768. 



The species of Scytonema diagnosed above has the longest 

 cells of all of the known species and is closely related to S. pul- 

 chellum. 



