ble mineral substances which the soil contains, gives a measure of
the directly nourishing capacity or fertility of a soil.

At the commencement of this century Theodore de Saussure
already perceived the importance of soluble inorganic or mineral
substances in soils in relation to the vegetation of plants, inasmuch
as he considered them as directly nourishing substances, without
which vegetable life could not exist. Before this time the gravest
philosophers entertained the opinion that mineral matter in plants
were only accidental circumstances, or, that if they were necessa-
ry, the plant had the power of transforming one into another,
or indeed of creating them. They believe that there was some-
thing in the force of the vital principle, which could change iron
into lime, lime into sand, or sand into potash, to supply the wants
of the plant. The mineral theory was, however, attacked by many
authorities, but recently it was brought to perfect proof by Wieg-
mann and Polstorff. These gentlemen have proved by direct ex-
periments that plants will die if they cannot obtain the necessary
quantity of mineral substances from their surrounding soil. The re-
sults of observations made by the Prince of Salm-Hortsmar, in this
matter are especially interesting, and may be given in the follow-
ing summary: In a mixture containing all the various substances
which are required by plants as nourishments, except silicic acid,
plants of oats remained low, pale and dwarfish; without lime, they
died after the second leaf; without potash and soda, they reached
only a height of three inches; without magnesia, they remained
weak and lying down; without phosphoric acid, very weak, but
upright and of normal formation; without sulphuric acid yet weak-
er, upright and of normal formation, but without fruit; without
iron, they remained very pale, weak and badly formed, and
without manganese, they did not reach their full strength and
showed but a few flowers. Soda could not represent potash in re-
lation to the strength of the plants. Magnesia could not repre-
sent lime. If, however, all of the mineral substances which vege-
table life requires were present in their proper proportion; and
sufficient quantity, the plants of oats reached a complete and pret-
ty luxurious development, even with an entire absence of humus
or any vegetable substance in the experimental mixture.

As to the character of the solution in which those nourishing
substances are absorbed by the plants, it has been stated by Bous-
singault, that annually by a good crop of one hectare* about 200
kilogrs.† of soluble mineral substances are taken away. But du-
ring the growth of these reaped plants, about six millions kilogrs.
of water were evaporated from the surface of their leaves; a quantity
which previously was taken from the soil before it could evaporate
from the leaves, and which always contained some soluble mineral
substances in solution, which Were left behind in the plants.

*One Hectare is about 2½ acres.        †One Kilogramme is equal to 2½ lbs.

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