limited, the plant soon reaches its full growth,
while if their supply is continued, a greater amount of elements
necessary to enable it to appropriate atmospheric nourishment being
obtained, its development proceeds much further. The quantity, or
mass of seed produced, will correspond to the quantity of mineral
constituents present in the plant. That plant, therefore, containing
the most alkaline phosphates and earthy salts will produce more or a
greater weight of seeds than another which, in an equal time has
absorbed less of them. We consequently observe, in a hot summer,
when a further supply of mineral ingredients from the soil ceases
through want of water, that the height and strength of plants, as
well as the development of their seeds, are in direct proportion to
its absorption of the elementary parts of the soil in the preceding
epochs of its growth.

The fertility of the year depends in general upon the temperature,
and the moisture or dryness of the spring, if all the conditions
necessary to the assimilation of the atmospheric nourishment be
secured to our cultivated plants. The action of humus, then, as we
have explained it above, is chiefly of value in gaining time. In
agriculture, this must ever be taken into account and in this
respect humus is of importance in favouring the growth of
vegetables, cabbages, &c.

But the cerealia, and plants grown for their roots, meet on our
fields, in the remains of the preceding crop, with a quantity of
decaying vegetable substances corresponding to their contents of
mineral nutriment from the soil, and consequently with a quantity of
carbonic acid adequate to their accelerated development in the
spring. A further supply of carbonic acid, therefore, would be quite
useless, without a corresponding increase of mineral ingredients.

From a morgen of good meadow land, 2,500 pounds weight of hay,
according to the best agriculturists, are obtained on an average.
This amount is furnished without any supply of organic substances,
without manure containing carbon or nitrogen. By irrigation, and the
application of ashes or gypsum, double that amount may be grown. But
assuming 2,500 pounds weight of hay to be the maximum, we may
calculate the amount of carbon and nitrogen derived from the
atmosphere by the plants of meadows.

According to elementary analysis, hay, dried at a temperature of 100
deg Reaumur, contains 45.8 per cent. of carbon, and 1 1/2 per cent.
of nitrogen. 1