132 
to protect the soil from the direct rays of the sun, thus conserving 
the moisture and giving the rhododendron roots the cool condi- 
tions which they require for the best development of the plants 
and acidity of the soil. 
GEORGE V. NasH 
REPORT ON AN EXPEDITION TO PORTO — FOR 
COLLECTING FRESH-WATER ALGA 
Dr. N. L. Britton, Director-in-Chief: 
Sir: The fresh-water algae of Porto Rico have hitherto been 
little known. P. Sintenis collected during his botanical travels 
in Porto Rico, 1884-87, some Characeae and other more conspic- 
uous fresh-water algae at different places on the isla e 
Characeae were later determined and described by Nord- 
stedt an r algae by ébius. Among the materila 
of Utricularia, collected by Sintenis, Lagerheim found in- 
termixed a larger number of species of algae than those contained 
n the alga collection proper. In nly seventy-seven 
species of C and ot ther fresh- eate algae have bee 
was therefore with great aie and great expectations 
that I accepted from you, Dr. Britton, the offer of a three months’ 
commission to collect fresh-water algae in Porto Rico for the 
New York Botanical Garden. 
I arrived at San Juan in the evening of the 23d of December 
Desmidiaceae, etc., near Borinquen Park, and pools at Rio 
iedras. the last mentioned place, a ditch close by the 
species of the ae viz., Compsopogon, and slime-balls of 
Stigeoclonium as large as walnuts. 
ill more ee were the artificial water basins at Rio 
