ON SOME ALGAL STALACTITES OF THE YELLOW- 
STONE NATIONAL PARK. 
JOSEPHINE E.. PIL DEN. 
(WITH PLATE VIII) 
DurinGc the summer of 1896, while making a collection of 
alge living in the hot waters of Yellowstone Park, a curious 
phenomenon of algal growth was observed which, it is thought, 
is worthy of being recorded. It was the production by certain 
species of alge of thalloid structures which, both from their 
appearance and their method of development, may be termed 
stalactites. 
The most characteristic forms noticed occurred in a small 
cave made by the cone of a geyser. The entire inner surface of 
the roof was coated with the alga, which formed shining black 
sheets or pendant masses of true stalactitic appearance (jig: I). 
They looked not unlike a group of icicles depending from some 
ledge. Indeed, the arrangement of the grouping was quite 
similar, but as far as individual shape is concerned the algal 
thalli were much shorter, thicker, and more broadly conical than 
the common icicle form. Then, too, this typical shape showed 
variation in two directions. Many were mere knob-like processes, 
as large as one’s fist, perhaps, while some formed masses of 
small, fleshy, toothed appendages. The plants chiefly concerned 
in the building up of these stalactites were Schizothrix calcicola, 
Gleocapsa violacea, and Synechococcus aeruginosus. 
In order to explain the probable cause of this formation, it 
will first be necessary to call attention to a peculiar method of 
_ growth which characterizes species belonging to the group 
Oscillariez, and then to describe a little more fully the habitation 
of the alge in question. 4 
It is well known that when a bit of living Oscillatoria, Phor- 
194 . [ sEPTEMBER 
Pe a ee 
