Oct., 1922] TURNER EFFECTS OF CERTAIN MINERAL SALTS 
443 
a certain amount, which is adequate in the low-nitrate solution; thus 
nitrates do not seem to become the limiting factor at the concentrations used. 
Summary and Conclusions 
1. Very few researches have been carried on to determine the factors 
which affect the ratio of top growth to root growth in plants. A solution 
of this problem is of interest both to the plant physiologist and to the 
practical plant grower. 
2. The purpose of the present study is to determine more exactly how 
increasing the nitrate content of a nutrient solution that is otherwise 
adequate for plant growth will affect the actual top and root growth as 
well as the ratios of top to root growth ; and further to suggest an explanation 
of the mechanism of the results obtained. 
3. Definite effects of particular mineral nutrients, under controlled 
conditions, upon top-root ratios, have been given little attention, though 
work has been reported as to the effect of poor soil and of a decrease in 
concentration of the nutrient solution. 
4. It has not been satisfactorily demonstrated that decreased concentra- 
tion as such will decrease the ratio of tops to roots in plants; on the other 
hand, it has been demonstrated in the present set of experiments that 
decreased concentration is ineffective in contrast with nitrate ions. 
5. A combination of nutrient salts is devised and used whereby nitrate 
ions may be increased or diminished widely without disturbing very much 
the other components of the solution. 
6. In all cases, barley and corn show significant increases in ratio of 
tops to roots as nitrate concentration of the solution is increased. This 
effect of nitrates was shown to be independent of the total concentration of 
the solution, and independent of the hydrogen-ion concentration. 
7. Flax grown for 41 days did not show an increase in ratio of tops to 
roots as nitrate content of the solution was increased, nor was there an 
increase with age after 21 days. 
8. The efficiencies of the three solutions, as judged by total dry weights 
of tops and roots, were not greatly different. 
9. Roots were grown in pure cultures with a supply of sugar. Some 
had plumules only removed ; others had plumules and endosperms removed ; 
in the third set, only the tips of the roots (2 cm. to 3 cm.) were employed. 
The results showed clearly that nitrates do not check, directly, root growth ; 
but they increased the growth of roots in all cases. 
10. The fact is brought out that neither dry weight nor length of root 
is a safe measure of growth in plants. 
11. Evidence has been given in these experiments that roots grown in 
pure cultures, in absence of light, are able to utilize the nitrates and carbo- 
hydrates present in the solution for growth and respiratory processes. 
