270 
R. H. TRUE AND H. H. BARTLETT 
action of the salt. This supposition was supported by the decrease^l 
root growth and by the appearance of pathological symptoms char- 
acteristic of Mg injury. In a mild degree of injury the xylem at the 
base of the hypocotyl and more especially in the upper part of the 
primary root showed a more or less extensively developed yellowish- 
brown discoloration. As the injury became more serious this staining 
of the tissues worked to the surface near the union of the radicle and 
the hypocotyl and appeared as a blotch of reddish-brown color. In 
the stronger solutions the surface of the radicles showed sunken areas 
having a reddish-brown color. In this experiment the staining of the 
xylem appeared in the roots even in the most dilute magnesium 
sulphate solution. The blotching at the union of the hypocotyl and 
primary root came clearly into view in the 4SM X io~^ solution and 
in the concentrations showing the maximum absorption, the injury was 
very marked and the development of lateral roots was almost sup- 
pressed . 
The course of the curve showing the average growth made by the 
roots indicated little tendency on the part of the MgS04 to help 
growth, the result showing at no point any marked superiority over 
the growth in the distilled water check. 
MgS04 seemed to act like calcium in so far that it permitted the 
roots to make a net absorption, but at the concentrations most favor- 
able to absorption the toxicity interfered with the health of the root. 
Thus the usefulness of Mg, in the absence of other + ions, seems to 
depend on its occurrence in great dilution. 
The fact that Mg(N03)2 and MgS04 closely parallel each other 
in their action seems to make it clear that the specific characteristics 
seen in both are preponderantly due to the Mg ion. 
Potassium Nitrate. Experiment 7 
The series of thirteen solutions of potassium nitrate studied in- 
creased in concentration from 32 to 4.16M X lO"^ with an interval of 
32 M X io~^ between members of the series. The experiment ran 
fifteen days. 
The results presented graphically in figure 7 show that potassium 
nitrate exerted an action on lupine roots markedly different from that 
seen in the cases of calcium and magnesium salts. In the weaker 
solutions (32 to 160M X io~^) the plants behaved very much as they 
do in distilled water. During the first four or five days the roots 
