434 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
those in the low-nitrate solution seemed slightly more vigorous and had 
slightly longer tops for each series, as well as longer roots. The lengths of 
tops and roots are given for two series : 
Sol. I 
(Low N.) 
Sol. II 
(Med. N.) 
Sol. Ill 
(High N.) 
Series 2 (36 days) 
Series 3 (41 days) 
Tops 
Roots 
Tops 
Roots 
19 cm. 
26.3 " 
21.3 " 
28.6 " 
17.5 cm. 
20 " 
19.6 " 
26.5 " 
17.5 cm. 
18.3 
19-3 " 
18.5 " 
Table 7 gives the green weights and dry weights obtained in this ex- 
periment. It will be noticed that this plant makes no appreciable response, 
in the ratio of tops to roots, to increa ed nitrate content of the solution. 
In other words, it would seem that in the case of flax we are dealing with 
a plant of an entirely different physiological constitution in so far as its 
ability to utilize nitrates is concerned. To what range it might respond, 
the limits of this experiment have not permitted investigation, but this 
fact presents a very interesting problem from the standpoint of flax nutrition 
(table 7). 
Studies to Determine the Direct Effect of Nitrates upon Root Growth by 
Growing Roots of Certain Plants in Pure Cultures 
Data submitted in the foregoing experiments show conclusively that 
concentration of nitrate ions in the nutrient solutions used, regardless of 
the total salt concentration of the solution, was the determining factor in 
altering the ratios of top growth to root growth in barley and corn. These 
experiments do not give evidence, however, as to how this alteration comes 
about. The writer has, therefore, carried out another set of experiments 
with the hope of finding out whether nitrates check the growth of roots 
directly, or whether the greater ratio of tops to roots as well as the actual 
reduction in root growth in the higher-nitrate solution may be due chiefly 
to processes set up in the tops which affect the distribution of food between 
tops and roots. 
Several methods were followed in this phase of the work. The effort was 
( entered chiefly in removing the influence of tops and noting the effect of 
different treatments upon roots. 
For these experiments, the same high-, medium-, and low-nitrate mineral 
nutrient solutions were employed as in Experiment I, but to each solution 
glucose was added at the rate of 2 grams per 100 cc. of solution, to supply 
the carbohydrate which normally comes from the leaves. 
The cultures were grown singly in 250-cc. globe flasks, or in some cases 
in Erlenmeyer flasks, in 100 cc. of solution. The cleaned culture flasks 
