43 
even preventing the hatching of the eggs, operating, in short, 
very much as does the mosquito oil, which is now used so 
copiously and effectively in the Canal Zone. I communicated 
this find to Col. W. C. Gorgas, Chief Sanitary Officer of the 
Isthmian Canal Commission, who manifested much interest in 
the matter. All the specimens of this Azod/a that were collected 
were sterile and the determination of the species cannot be made 
with entire confidence. It is, however, larger and of a denser 
Fic. 15. A flood on the Chagres River, near Gatun, January 1, IgIo. 
habit of growth than the Azolla caroliniana of the United States 
and southward and is probably Azolla filiculoides, originally 
described from southern South America but now considered to 
range as far north as California. 
For various courtesies which facilitated our work in Colon and 
vicinity and added to the comfort of our stay there, we are 
especially indebted to Col. George W. Goethals, Chairman of the 
Isthmian Canal Commission, to Judge Thomas E. Brown, Jr., of 
