II2 BOTANICAL GAZETTE [SEPTEMBER 
1. The lack of or the deficiency of calcium in the nutrient media, 
It is in this sense that the injury to the seedlings grown in the 
solutions of potassium salts is to be accounted for, as it was obvi- 
ously not due to the presence of magnesium. Furthermore, as 
the cultures grown in the different solutions of calcium salts were 
not injured, this is suggestive that beneficial results should obtain 
from additions of calcium salts to nutrient solutions that have 
shown themselves to be poor media for plant growth because of 
excessive amounts of potassium or magnesium salts. Numerous 
tests have proved this to be true. This, however, does not neces- 
sarily imply any definite calcium-magnesium ratio or a calcium- 
potassium ratio as a condition of physiological importance in 
nutrient solutions. The amount of calcium ions needed to over- 
come the harmful effects of excessive concentrations of potassium 
ions or magnesium ions will be determined largely by other condi-_ 
tions or sets of conditions under which the plants grow, of which 
those affecting the rate of transpiration of the plants are not 
of least importance. 
2. The relation of phosphorus. A relatively high concentra- 
tion of magnesium ion and the absence of calcium (except a trace 
as an impurity) in the solutions are conditions supposed to be 
conducive to injury. As no abscission of the leaf tips appeared 
in the seedlings grown in solutions of MgHPO,, it appears that in 
the magnesium-phosphorus relation is a condition that in this case 
is physiologically important. It is hardly possible that the trace 
of calcium found in MgHPO, could account for these results. 
Equally large traces of calcium were found in the other salts used, 
especially K.SO,, which contained 0.005 per cent. As this amount 
did not prevent injury, it seems reasonable to discount the effect 
of a smaller trace of calcium found in MgHPO, as being the cause 
for the non-injury to the seedlings. The fact that KH,PO, pro- 
duced less injury than did any of the other potassium salts used 
presumably was due to some action involving the H,PO, ion. 
As the potassium salts and two of the magnesium salts used 
gave injury to the wheat seedlings, one can infer that this was due 
to some action of a positive ion of the salts in solution. On the 
other hand, certain positive ions, calcium for example, did not 
