96 BOTANICAL GAZETTE | FEBRUARY 
Subjected to chemical tests the incrustation is found to be 
made up almost wholly of calcium carbonate in the amorphous 
form, and organic material. It is exceedingly porous, absorbing 
water readily when dry, and is also very friable. 
A microscopical investigation shows the presence through- 
out the stratum of species of alge belonging to the Cyanophy- 
cez. Three species are found to be constant,a Dichothrix and 
two species of Lyngbya. Numerous diatoms and scattered cells 
of Glceocapsa are also present. The difference in color of the 
surface of the stratum is found to be due to the position of the 
above three species. When the Dichothrix appears on the sur- 
face a shade of light brown with a tinge of pink is given, or at 
times a bright czsius blue. The Lyngbyas occasion the zerugi- 
nous tints. 
The calcareous matrix contains constantly an organism evi- 
dently fungal in character and corresponding in all respects to 
the chlamydospore-bearing filaments of Pseudohelotium granu- 
losellum as figured by Brefeld.*. The extraordinary occurrence 
of this fungus I am quite unable to explain, and its origin and 
development in the matrix must receive further study before 
anything of importance can be said about it. 
In general the relative positions of the three algal species are 
as follows: the Dichothrix possesses the widest range and is the 
most abundant of the three. It occurs farthest from the light 
in the older portions of the lime stratum, as well as at the sur- 
face. Its arrangement is for the most part zonal. The filaments 
are parallel and stand perpendicular to the plane of the stratum. 
The large Lyngbya does not extend downward so far as the 
Dichothrix. It prefers, evidently, the area just beneath the sur- 
face of the crust, but at times it reaches the extreme surface. 
Its filaments form a tangled network. As a rule the small 
Lyngbya is found at the top of the matrix and immediately 
below the cae, — ieee filaments consist of empty 
sheaths. — 
The growth on the remaining three sides of the tank shows 
: ——- Heft 10, #2. 12, a fee 26. : 
