- 3 8 — 
In the accompanying illustration the distinguishing characters are all 
clearly marked, with the exception of the calyptra. The photographs were 
taken from dried herbarium material, a. P. brevicaule; b. P. brachyphyllum. 
Both four times natural size. 
New Dorp, N. Y., June, 1919 
MOSSES AS FORMERS OF TUFA AND OF FLOATING ISLANDS 
Aravilla Taylor 
In an article by W. H. Emig in The Bryologist of March, 1918, the author 
described certain species of moss, Didymodon tophaceus (Brid.) Jur. and Phil- 
onotis calcarea Sch., as rock builders in the waterfalls in the Arbuckle Mountains 
of Oklahoma. 
A somewhat similar, although probably a less extensive, formation has 
been observed in the outlets of various mineral springs in Indiana and Illinois 
where mosses aid in forming a rock-like tufa. 
At Otis, Indiana, and New Lenox, Illinois, there are numerous springs, the 
water of which is highly impregnated with iron compounds. In the outlet of such 
a spring is frequently found large quantities of Brachythecium rivulare B. & S. 
