1897] ALGAL STALACTITES OF YELLOWSTONE NATIONAL PARK 197 
at once. Some which showed well the characteristic shape was 
preserved in a solution of formalin for study in the laboratory. 
When first collected the algal growth showed the following 
features: The stratum was firm in substance; the entire surface 
of the sheet, teeth and stalactites was protected by a thin black 
membrane, fine in texture, smooth and shining; the inner parts 
were somewhat spongy, yet firm, and in color white, gray, or 
brownish, with violet, rose and blue-green tints in places. In 
making a cross section of astalactite a laminated appearance was 
noticed (fig. 2). The lamellae were numerous and very thin. 
Some of the most perfectly formed stalactites, though not the 
largest, measured from 5—8™ in length and 1.5—2™ in diameter. 
Upon returning to Minneapolis, a microscopic study of the 
formalin material showed that there were present a group of 
algae of which three members were constant. These were 
Schizothrix calcicola, Gleocapsa violacea, and Synechococcus aerugi- 
nosus, of which the following are descriptions based upon the 
Yellowstone material. 
SCHIZOTHRIX CALCICOLA(Ag.) Gomont Monographie des Oscil- 
lariées, Ann. Sci. Nat. (Bot.) VII. 15: 307. pl. 8. fig. 1-3. 1892. 
Tilden, Am. Alg. Cent. II, no. 180. 1896. (Plate VIII, figs. 3, 4-) 
Stratum not encrusted with lime, somewhat gelatinous, very 
hard when dried, membranaceous, black or dark violet. Filaments 
Strongly and sharply bent, interwoven ; sheath firm, straight, in 
the beginning somewhat narrow, cylindrical, including one 
trichome, with age growing thicker, becoming somewhat lamel- 
lose, including two to many trichomes; trichomes pale aerugin- 
ous (after remaining in formalin several months), neither atten- 
uate nor curved at the apex, not constricted at the dissepiments, 
1.6u in diameter ; articulations in general 1-2 times longer than 
the diameter ; apical cell rotund; dissepiments marked by pro- 
toplasmic granules. 
“It is the interwoven filaments of this plant alone which form 
the membrane of the stalactite. Empty sheaths are also pres- 
ent in great abundance throughout the whitish or light-colored 
interior. 
