1898] 



MICROSCOPICAL JOURNAL. 



10 



scalding water. The threads are cemented together by 

 the lime. 



Phormidium. — Another formation in the bottom and 

 sides of these hot pools is of a leathery, felty appearance 

 and shows many crystals of calcium carbonate (fig. 10, x 

 250 dia.). These filaments are less than 1-1, 000th of a 

 millimeter in diameter and are glued together. The sur- 

 face is smooth and slippery but gritty because of the 

 crystals of calcium carbonate. The cells of this organism, 



magnified appear elongated and of a greenish color. It 

 is Phormidium and akin to Oscillatoria — a very common 

 blue-green alga of stagnant water. The several species 

 of the Yellowstone are distinguished by the size of the 

 cells. The smallest, fig. 5, grow in water hot as 75° C. 

 The larger, fig. 6, are found in water not so hot. The 

 tint is at first bright green but later is brownish. Min- 

 eral deposits produce golden yellow color and dark red. 

 The sun will bleach them all white. 



Spirulina.-— Figure 7 shows another form, socalled 



