191 1] Carl L. Aisberg 99 



Menthol has been shown to be capable of oxidation to men- 

 thone. Since free menthol was slightly in excess in the oil of the 

 frozen plant, perhaps another effect of freezing is to lessen oxida- 

 tion in the plant tissues. 



Absorption and Excretion of Salts by Roots, as Influenced by 

 Concentration and Composition of Culture Solutions 



I. CONCENTRATION RELATIONS OF DILUTE SOLUTIONS OF 

 CALCIUM AND MAGNESIUM NITRATES TO PEA ROOTS 



R. H. TRUE AND H. H. BARTLETT 



(Office of Drng Plant, Poisonous Plant, Physiological and Fer- 

 mentation Investigations, Bureau of Plant Industry, 

 Department of Agriculture.) 



Secondary roots of the pea will not develop in m/5000 

 Mg(N03)2. A calcium to magnesium ratio of i/io is the lowest 

 ratio at which calcium entirely inhibits the harmful effect of 

 magnesium in Solutions of this concentration. In Solutions of such 

 concentration that magnesium alone would not prevent the forma- 

 tion of secondary roots (e. g., m/20,000) the calcium to magnesium 

 ratio which brings about perfect root development is nearer i/ioo. 

 In Solutions of whatever concentration the calcium to magnesium 

 ratio most favorable to absorption of salts is i/i. 



For calcium nitrate Solution used as a culture medium, or for 

 magnesium nitrate Solution, or for mixtures of the two in any ratio, 

 there is a definite concentration above which roots absorb more 

 electrolytes than they excrete and below which they excrete more 

 than they absorb. This equilibrium concentration is 12 m/500,000 

 for Mg(N03)2 and 7m/50,ooo for Ca(N03)2. For Solutions of 

 the two in the lowest ratio which permits perfect root development 

 (Ca: Mg: : I : 10) the equilibrium concentration is 8 m/500,000, 

 almost as low as for Ca(N03)2 alone. For Solutions mixed in the 

 most favorable ratio for absorption (f. e., 5/5) the equilibrium 

 concentration is 5 m/500,000, lower than for Ca(N03)2 alone. 



