1897 | SOME NEW SPECIES OF MINNESOTA ALG 99 
had a brown color. The change in color from z#ruginous to 
violet may have some connection with the approach of cold 
weather. It was also noticed that the sheath of the larger 
Lyngbya had become corrugated or roughened and somewhat 
wider. 
It is thought that these five alga, which have just been 
described, are capable, either alone or in combination, of caus- 
ing the precipitation of calcium carbonate. If the deposit is 
not formed in this way, it must be because the water contains a 
large quantity of calcium carbonate which is laid down as the 
result of evaporation. In this case these algz have become 
adapted to a life within a calcareous envelope. As a matter of 
fact the water is not rich in carbonates. An analysis kindly 
made for me by Professor G. B. Frankforter shows the following 
results: 
Total solids, = - - - - 36 grains per gallon. 
Calcium carbonate, - - Se serrate = 
Calcium sulphate, = - - - i es ™ 
Sodium chloride, - - . - trace. 
Magnesium sulphate, - - trace. 
Another fact in favor of the supposition that the plants act 
as agents in the deposition is that the precipitation of calcium 
carbonate takes place only where the plants occur, and not 
indiscriminately upon every object exposed to the action of the 
water. A dead branch of a tree, after being in the water a 
year, was taken out to be preserved. The top and sides, as it 
lay in the water, were covered with a luxuriant growth of the 
several blue-green alg and the Chetophora. On its under 
shaded surface the algz would not live, nor was there a trace of 
lime to be found there. Again, the water has formed a ditch 
around the outside of the tank, deep and narrow, and therefore 
dark. For the latter reason no algz grow on the back of the boards, 
and no deposit is formed there, though they are washed by the 
same water that circulates through the interior of the tank. 
In certain waters at Mammoth Hot Springs, Yellowstone Park, 
_where tourists suspend articles to be incrusted, the deposit coats 
