28 MISSOURI BOTANICAL GARDEN BULLETIN 
Group II. A salt of magnesium used alone is injurious at a 
lower concentration than any other mineral nutrient. About 
three-hundredths of one per cent of magnesium chloride 
practically prevents growth. The addition of a small amount 
of a calcium salt, however, entirely overcomes the injurious 
or toxic action of the magnesium; hence the calcium exhibits 
towards magnesium a strong antitoxic or antidotal action. It 
may seem remarkable that a single nutrient salt used in this 
way should not be able to induce an amount of growth equal 
at least to that occurring in distilled water, and more remark- 
able that it may entirely inhibit growth. Nevertheless, it is a 
general rule (calcium salts being an exception in certain 
cases) that plants and animals alike suffer injury in very 
weak solutions of the necessary mineral nutrients used singly. 
Group III. A sodium salt (for example, common table 
salt) used alone, is less injurious than the same concentration 
of magnesium, but it is nevertheless distinctly injurious at 
five-hundredths of one per cent. In this case also, calcium is a 
strong antitoxic agent, so that in the presence of calcium it is 
possible for plants to grow at much higher concentrations of 
sodium. 
Group IV. The remarkable property shown by calcium of 
antagonizing other mineral bases is exhibited to a lesser de- 
gree by most of the other bases as well, thus potassium and 
magnesium are to a certain extent mutually antagonistic, so 
that a mixture of the two is never as toxic as either alone. 
The corrective effect of the one substance on the other is 
obvious, even though the growth in the mixed solution may 
not be equal to that in distilled water. 
Group V. Barium, although related to calcium, is in 
reality a very injurious mineral with respect to plant growth, 
but in this case, also, the plant will endure much stronger so- 
lutions of the poison in the presence of calcium. | 
Group VI. The metal manganese is about as injurious as 
barium, but its action is ally interesting on account of 
the fact that even at great dilution it induces a yellowing, or 
chlorosis, of the leaves. Again, at a somewhat higher con- 
centration it inhibits effectively the growth of shoots, al- 
though permitting normal root development. Calcium is 
here, as in the case of magnesium, sodium, and barium, the 
strongest antidote known. 
Group VII. In a ere full nutrient solution there is a 
very complex and aa y balanced state of affairs, each sub- 
stance tending to check any possible injurious action of cer- 
