JULY 30, 1897. ] 
of the cells are sulphur granules. If our 
plant is not Beggiatoa it would be classified 
as a Bacillus because of the rod-like char- 
acter of the cells. The writer will not at- 
tempt to name it on the insufficient data, 
and it serves as an excellent illustration of 
the difficulties with which one contends in 
attempting to define precisely the relations 
of these organisms to one another. Itisa 
very interesting form from its habits and 
its habitat, and probably the most adven- 
turous organism in the hot springs. 
This peculiar species of the bacteria 
leaves a record of itself in the mineral de- 
posits in the following manner. ‘The fila- 
ments, at first delicate and exceedingly flex- 
ible, become coated with such a thick 
deposit of sulphur and calcium carbonate 
that they lie as stiff fibers along the edges. 
of the hot pools and upon the bottom of 
the streams. Sometimes the collections of 
these filaments have the appearance of frost 
work in the scalding hot water. Eventu- 
ally the threads become cemented together 
by the continual deposition of lime, but 
they impress their individuality upon the 
resulting formation by giving it a fibrous 
structure. These points are well illustrated 
by the photograph of a piece of formation 
shown in Fig. 5. 
The tufts of waxy bacterial filaments are 
often associated with extensive growths of 
quite a different character. Large areas 
upon the sides and bottoms of the pools and 
streams are frequently covered by a closely 
packed felt of extremely delicate filaments. 
The surface is smooth and slippery, and it 
feels like a sheet of rather stiff jelly all 
gritty because of the numerous crystals of 
calcium carbonate deposited in the sub- 
stance. Under magnification the true struc- 
ture is made apparent, and one sees here a 
closely woven mass of very minute fila- 
ments agglutinated together. The indi- 
vidyal filaments are sometimes less than 
one-thousandth of a millimeter in diameter, 
SCLENCE. 
151 
so that they look like mere lines even under 
a magnification of 200 to 300 diameters. 
Fig. 6 illustrates the general appearance of 
the leathery felband shows the many crys- 
tals of calcium carbonate imbedded in the 
mass of filaments. The cells of this plant 
are several times longer than broad and the 
color is greenish. The genus is called Phor- 
nmidium and contains forms closely related 
to a very common blue-green alga of stag- 
nant waters, named Oscillatoria. There are 
several species of Phormidiwmnin the hot 
springs, differing from one another chiefly 
in the measurement of the cells. The 
smallest forms, such as are shown in Fig. 
4—c, are found in water as hot as 75° C., 
while the larger types (Fig. 4-d) only in- 
habit water that is several degrees cooler. 
The color of the Phormidiwm growtks is 
quite variable. When actively vegetative 
the tint is bright green, but older sheets 
become brownish and the presence of vari- 
ous mineral deposits give the growths shades 
of golden yellow and dark red. If dried in 
the sun the colors fade out through various 
tints of yellow and pink to the everlasting 
white of the formation. 
Another interesting plant frequently 
makes itself prominent, side by side, with 
the Phormidium. It is called Spirulina and, 
as the name suggests and the figures (Fig. 
4-e) show, the form is a filament closely 
coiled in a spiral. This organism has the 
power of forward movement, the free ends 
swinging from side to side in such a man- 
