PORTO RICO AGRICULTURAL EXPERIMENT STATION. 
[Under the supervision of A. C. True, Director of the States Relations Service, United States Department 
of Agriculture.] 
E. W. Allen, Chief of Office of Experiment Stations. 
Walter H. Evans, Chief of Division of Insular Stations, Office of Experiment Stations. 
STATION STAFF. 
D. W. May, Agronomist in Charge. 
P. L. Gile, Chemist. 
W. V. Tower, 1 Entomologist. 
H. E. Thomas, Plant Pathologist. 
H. C. Henricksen, Specialist in Farm Management. 
W. A. Mace, Agricultural Technologist. 
T. B. McClelland, Horticulturist. 
J. O. Carrero, Assistant Chemist. 
W. P. Snyder, Assistant in Plant Breeding. 
C. Alemar, Jr., Clerk. 
LETTER OF TRANSMITTAL. 
Porto Rico Agricultural Experiment Station, 
Mayaguez, P. R., February 13, 1917. 
Sir: In the present diligent search for all possible sources of fertilizing material, 
natural deposits, especially of phosphates, are of special interest. One of the natural 
resources of Porto Rico is the guano deposited by bats in the many caves of the lime- 
stone sections. These guanos have been used as fertilizers for years, but without a 
clear conception of their value or the manner in which they can be employed best. 
This manuscript gives the results of extended studies on the composition and fer- 
tilizing value of these deposits and should prove of considerable value as a guide to 
Porto Rican planters. I recommend that it be published as Bulletin No. 25 of this 
station. 
Respectfully, 
D. W. May, 
Agronomist in Charge. 
Dr. A. C. True, 
Director States Relations Service, 
U. S. Department of Agriculture, Washington, D. C. 
Recommended for publication. 
A. C. True, Director. 
Publication authorized. 
D. F. Houston, 
Secretary of Agriculture. 
» Appointed Mar. 1, 1918, to succeed R. H. Van Zwaluwenburg, transferred to United States Depart- 
ment of Agriculture, Bureau of Entomology. 
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