SOME ASPECTS OF THE SALT REQUIREMENTS 
OF YOUNG RICE PLANTS? 
By RAFAEL B. EsPINo 
Of the College of Agriculture, Los Banos 
ONE PLATE AND NINE TEXT FIGURES 
INTRODUCTION 
One of the most important human activities has long dealt with 
the improvement of methods for securing plant products upon 
which human nutrition depends. The scientific problems of the 
nutrition of plants are thus closely connected with the practice 
of agriculture, and agriculturists as well as plant physiologists 
have already accomplished much toward outlining and solving 
some of these problems, with reference to many different kinds 
of plants. The mineral nutrition and the salt requirements of © 
plants have recently received a great deal of attention, and the 
methods employed in experimentation in this field are being rap- 
idly improved. Among the methods that have yielded valuable 
results as to the physiological needs of plants the so-called 
“water-culture”’ method is important. By this method the cul- 
ture plants are grown with their roots in aqueous solutions of 
various inorganic salts, in various proportions, these solutions 
having various total concentrations. This may be called the 
method of solution cultures, although of course the source from 
which the plants absorb their mineral nutrients is an aqueous 
Solution even -when soil or sand is used. “Water culture” is 
employed in a general sense to denote such solution cultures, 
but, as Shive* has pointed out, actual water cultures (with 
distilled or otherwise purified water) are seldom of much value 
in nutritional experimentation, partly because pure water not 
* Botanical contribution from the Johns Hopkins University, No. 61. 
A brief preliminary report of some of the results presented in this paper 
was given before the 1918 (Baltimore) meeting of the Physiologica] Sec- 
tion of the Botanical Society of America. 
*Shive, John W., A study of physiological balance in nutrient media, 
Physiol. Res. 1 (1915) 327-397, 331. See also True, R. H., Harmful action 
of distilled water, Am. Journ. Bot 1 (1914) 255-273; Hibbard, R. P., The 
question of the toxicity of distilled water, ibid. 2 (1915) 389-401. 
171114——2 455 
