678 Our Fresh-Water Alge. 
immense numbers however ; sometimes the whole surface of a lake 
is covered with them. For several years a little pond near Wash- 
ington attracted my notice by its uniform dingy green ; examination 
y the microscope proved regularly that it was due to presence of 
myriads of a very minute alga, a Staurastrum, a pretty little desmid 
with six radiating points of green. The Bavarian lake, the Schlier- 
see, grew turbid under the ice of the winter before the present, 
acquiring a general green or blue, due, suggests Dr. Harz, to 
enormous quantities of the microscopic alga Palmella uveeformis : 
then the color changed under the ice to a yellow-red and at last to 
peach-color from the incoming of another alga, Clathrocystis roseo- 
persicina, which is said to have attacked and destroyed the other. 
This fittest survivor, conqueror in the battle of the algal hosts under 
the ice, was found lurking in wide expanses of beautiful peach color 
on the mud bottom of Babcock Lake here in Washington, recently 
drained to assure the safety of the Washington monument. The 
green surfaces of stagnant pools everywhere familiar, are also 
examples of minute algæ occurring in vast masses. 
The larger species may be mounted on cards or sheets of unglazed 
paper as is so common with the marine alge ; or on sheets of mica 
for coarser microscopic examination; or preserved for the same 
purpose in bottles of carbolized water. My practice is, however, to 
preserve specimens forthe microscope, large or small, in cement cells, 
using as a medium King’s fresh-water alge fluid; specimens of 
three or four years’ standing still remain unchanged. Some species 
may be collected throughout the year, even under the ice ; in the 
city of Washington many are constantly abundant as green coatings 
on trees, walls and stone steps ; others live in the drinking fountains, 
species, as Draparnaldia plumosa, which exist only in pure water ; 
others are to be sought on the damp wood work of pumps; still 
others in the conservatories, on damp bricks and flower-pots and m 
the soil. The mud of the Potomac margin contains its own species 
and there the Vaucheria waves in profusion ; Oscillarias, Palmellas, 
and other unicellular species abound; and outside of the city, 
springs, streams and pools are each full of their treasures, wet ban 
and even meadows yield their own peculiar species ; and the early 
spring pools filled by Potomac overflows are especially the haunt 
of the Algee. 
