68 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
relatively small effect of large amounts of iron and aluminum salts when 
added to this solution confirms the well known power of calcium- and phos- 
phoric-acid soil amendments to precipitate and render harmless any heavy 
metals which may be present in the soil. 
The relative amount of transpiration is in most cases closely related to 
the yield. In the solution cultures, there seems to be a tendency for the 
transpiration to be depressed more than the yield. 
No important specific pathological conditions were observed in any of 
the acid cultures. In plants grown in the solution cultures containing 
toxic concentrations of iron salts, zone ''B" of the lower nodes was in- 
variably discolored brown or reddish brown. The number of discolored 
nodes varied. In some cases, almost every node was discolored: the upper 
ones almost a rose color, the lower much darker. In no other cultures did 
discolorations of this type appear. In the sand cultures the results were 
very similar except for the lesser discoloration by the ferric salts. A 0.0002 
N ferrous sulphate solution caused a reddish-brown discoloration of all the 
nodes from which roots arose in four of the ten plants. The 0.0004 N 
solution discolored the lower nodes in all the plants and some of the nodes 
above the roots in three. It is very likely that if the plants had been grown 
for a longer period, these cultures would not have produced relatively as 
good a growth in comparison with the control. The 0.0004 ^ ferric solu- 
tions did not produce any discoloration. The nodes, however, did show a 
strong accumulation of iron in the node when haematoxylin was applied 
after the method of Moore ('14). In some of the more toxic concentrations 
of the acids and of the aluminum salts, plants w^ere found, occasionally, 
in which the lowest nodes were somewhat yellow or a yellowish brown. 
Pieces of these nodes were placed on agar slants by Dr. Alice M. Russell. 
In most instances yellow colonies of bacilli developed on the slants. Dr. 
Russell believes that these organisms were largely responsible for the yellow 
discoloration. Pieces from the nodes discolored by iron were also placed 
on agar by Dr. Russell. Organisms were secured in only a very few in- 
stances. This fact, and the^ absence of a reddish-brown discoloration in 
all solutions not containing iron in toxic concentrations, seem conclusive 
proof that the iron salts are the primary cause of this pathological condition. 
Michrochemical tests made by the method developed by Carr^ on the plants 
grown in the solutions containing the aluminum salts, showed that aluminum 
collected in zone "B" similarly to the iron salts but produced no discolora- 
tion. Chlorotic plants were commonly found in the cultures containing 
2 The test used was developed by Dr. R. H. Carr of the Ofhce of Cereal Investigations, 
U. S. Department of Agriculture. The distribution of iron was determined microchemically 
in one half of the stem by an acidulated solution of KCNS. The other piece was then 
boiled in a saturated solution of (NH4)2C03 to which a small quantity of haematoxylin was 
added. Carr's analyses have shown that any increased discoloration produced by the 
second test indicates the presence of aluminum. 
