26 MISSOURI BOTANICAL GARDEN BULLETIN 
A DEMONSTRATION OF SOME IMPORTANT RELA- 
TIONS OF PLANTS TO LIME AND OTHER 
SOIL NUTRIENTS 
During the present month, and continuing into March, 
there are on exhibit in the south wing of the new greenhouses 
some demonstrations illustrating in a convincing manner 
some of the most important relations of plants to the mineral 
fertilizers and other growth factors of the soil. In general, 
these experiments are designed to show, among other facts, 
what elements of the soil are essential in plant growth; the 
relation of growth to a variety of soil factors, especially the 
deleterious action of the essential salts when these are used 
singly rather than in a properly balanced ratio; and the im- 
portance of a neutral or alkaline condition (attained by lim- 
ing) for the best growth of certain plants, as conteesiok with 
acidity, which is requisite for others. 
The Nature of Plant Substance——The bulk of any green 
herbaceous plant is water, 60-90 per cent ordinarily, and in 
the case of cress or cucumber this may amount to more than 
90 per cent of the total weight. Organic or combustible sub- 
stance, as we may roughly designate it, constitutes commonly 
from 10-20 per cent of succulent plants; while the mineral or 
salt content of fresh plant tissues is usually less than 2 per 
cent. But the mineral “plant foods,” or nutrients, are as 
necessary as the organic matter and the water. However, the 
green plant makes its organic food through the use of the 
carbon dioxide of the air as raw material, while the mineral 
constituents are, like the water, derived from the soil. To this 
fact is due in part the importance of a proper soil in the pro- 
duction of plants. Soils are most diverse, and not merely so 
with respect to color and origin. More important are the dif- 
ferences in texture and water content; the form, availability, 
and relative concentration of the mineral constituents; the 
presence of organic matter; the occurrence of compounds in- 
jurious to plant growth; and the activity of micro-organisms. 
In any case the soil solution, that is, the water of the soil, 
must, of course, contain any soluble substance present in the 
soil. Moreover, such constituents enter the plant only in so- 
lution. If we grow plants to demonstrate or determine their 
mineral requirements, it is well to employ water cultures to 
which we may add just those substances the effects of which 
we wish to observe. Water cultures have been most valuable 
in shedding light on various problems relating to plant life, 
and they are most convenient for our purpose here. _ 
Methods.—The methods involved are simple. Tumblers 
or glass cylinders are used as containers for the culture solu- 
