170 HOW CROPS GROW. 
a maize plant, five and three quarters feet high, and equal 
in every respect, as regards size, to plants from similar 
seed, cultivated in the field. The ears were not, however, 
fully developed when the experiment was interrupted by 
the plant becoming unhealthy. 
With the oat his success was better. Four plants were 
brought to maturity, having 46 stems and 1535 well-devel- 
oped seeds. (Vs. St., VIII, 190-215.) 
In similar experiments, Nobbe obtained buckwheat 
plants, six to seven feet high, bearing three hundred plump 
and perfect seeds, and barley stools with twenty grain- 
bearing stalks. (Vs. S¢., VII, 72.) 
In water-culture, the composition of the solution is suf 
fering continual alteration, from the fact that the plant 
makes, to a certain extent, a selection of the matters pre- 
sented to it, and does not necessarily absorb them in the 
proportions in which they originally existed. In this way, 
disturbances arise which impede or become fatal to growth. 
In the early experiments of Sachs and Knop, in 1860, they 
frequently observed that their solutions suddenly acquired 
the odor of sulphydric acid, and black sulphide of iron 
formed upon the roots, in consequence of which they were 
shortly destroyed, This reduction of a sulphate to a sul- 
phide takes place only in an alkaline liquid, and Stohmann 
was the first to notice that an acid liquid might be made 
alkaline by the action of living roots. The plant, in fact, 
has the power to decompose salts, and by appropriat- 
ing the acids more abundantly than the bases, the latter 
accumulate in the solution in the free state, or as carbon- 
ates with alkaline properties. 
To prevent the reduction of sulphates, the solution must 
be kept slightly acid, best by addition of a very little free 
nitric acid, and if the roots blacken, they must be washed 
with a dilute acid, and, after rinsing with water, must be 
transferred to a fresh solution. 
On the other hand, Kiihn has shown that when chloride 
