om these considerations have been further
confirmed by the direct experiments of different observers. Boussingault
sowed peas, weighing 15.60 grains, in a soil composed of a mixture of
sand and clay, which had been heated red-hot, and consequently contained
no humus, and after 99 days' growth, during which they had been watered
with distilled water, he found the crop to weigh 68.72 grains, so that
there had been a fourfold increase. Similar experiments have been made
by Prince Salm Horstmar, on oats and rape sown in a soil deprived of
organic matter by ignition, in which they grew readily, and arrived at
complete maturity. One oat straw attained a height of three feet, and
bore 78 grains; another bore 47; and a third 28--in all 153. These when
dried at 212 deg. weighed 46.302 grains, and the straw 45.6 grains. The most
satisfactory experiments, however, are those of Weigman and Polstorf,
these observers having found that it was possible to obtain a
two-hundred-fold produce of barley in an entirely artificial soil,
provided care was taken to give it the _physical_ characters of a
fertile soil. They prepared a mixture of six parts of sand, two of
chalk, one of white bole, and one of wood charcoal; to which was added a
small quantity of felspar, previously fused with marble and some soluble
salts, so as to imitate as closely as possible the inorganic parts of a
soil, and in it they planted twelve barley pickles. The plants grew
luxuriantly, reaching a height of three feet, and each bearing nine
ears, containing 22 pickles. The grain of the twelve plants weighed 2040
grains.

These experiments show that plants can grow and produce seed when the
most scrupulous care is taken to deprive them of every trace of humus.
But Saussure has gone further, and shown that even when present, humus
is not absorbed. He allowed plants of the common bean and the Polygonum
Persicaria to grow in solutions of humate of potash, and found a very
trifling diminution in the quantity of humic acid present; but the value
of his experiments is invalidated by his having omitted to ascertain
whether the diminution of humic acid which he observed was really due
to absorption by the plant. This omission has been supplied by Weigman
and Polstorf. They grew plants of mint (Mentha undulata) and of
Polygonum Persicaria in solutions of humate of potash, and placed beside
the glass containing the plant, another perfectly similar, and
containing only the solutio