LETTER OF TRANSMITTAL. 
U. S. DEPARTMENT OF AGRICULTURE, 
BuREAU OF PLANT INDUSTRY, 
OFFICE OF THE CHIEF, 
Washington, D. C., July 24, 1911. 
Sir: I have the honor to transmit herewith and to recommend for 
publication as Bulletin No. 231 of the special series of this Bureau a 
manuscript by Dr. Rodney H. True, Physiologist, and Mr. Harley 
Harris Bartlett, Chemical Biologist, entitled ‘‘ Absorption and Excre- 
tion of Salts by Roots, as Influenced by Concentration and Composi- 
tion of Culture Solutions. J.—Concentration Relations of Dilute 
Solutions of Calcium and Magnesium Nitrates to Pea Roots.” 
This paper, submitted by the Physiologist in Charge of Drug-Plant, 
Poisonous-Plant, Physiological, and Fermentation Investigations, is to 
be followed by others under the same general title. The entire series 
will deal with problems of plant nutrition which have an important 
bearing upon the theory and practice of agriculture. 
Respectfully, 
B. T. GaLLoway, 
Chief of Bureau. 
Hon. JAMEs WILSON, 
Secretary of Agriculture. 
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