«889.] The Vegetation of Hot Springs. 395 
to all other forms of life. The ability possessed by the vege- 
tation found in such waters to withstand such extreme and 
adverse conditions of environment shows the possible exist- 
ence of this form of life during the early history of our globe, 
when the crust of the earth is supposed to have been cov- 
ered with hot and highly mineralized waters. Such plants 
may thus represent the earliest links in the chain of evolu- 
While the mosses Hypnum and Sphagnum have been found 
in warm waters (go'^-ioo'' Fahr.), the vegetable life of hot 
water consists wholly of fresh water algae. Such plants are 
usually less striking in appearance than the sea-weeds, but 
assume most curious and interesting forms when subjected to 
the peculiar conditions that prevail in hot springs. 
It has long been known that algae occur in hot waters, and 
the descriptions of hot springs given by travelers often con- 
tain allusions to the presence of bright green "conferva" 
living in the hot pools and streams. Algae are common also 
in the hot waste waters flowing from many mills, the brilliant 
green growths lining the conduits. Where the plants present 
in thermal waters are of this color, their vegetable nature 
seems to have been readily recognized; but there is good 
reason to believe that the existence of algae of other colors, 
particularly the pink, yellow and red, forms so common in the 
Yellowstone waters, have been overlooked or mistaken for de- 
posits of purely mineral matter. That such is the case is not 
■at all surprising, for the plants often surround themselves with 
■a hyaline gelatinous envelope, or are encrusted and hidden by 
mineral matter extracted from, or deposited by, the hot 
waters, and sometimes obscuring the plant growth so com- 
pletely that the organic nature of the substance is scarcely 
recognizable even by an algologist. Thus the Beggiatoa;, the 
characteristic vegetation of sulphur springs, were long con- 
sidered a lifeless organic slime. Their silky threads are often 
completely hidden by grains of sulphur, or entombed beneath 
a deposit off 
