The Formation of Vegetable Mould Through the Action of Worms: With Observations on Their HabitsDarwin, Charles
Science
The Formation of Vegetable Mould Through the Action of Worms: With Observations on Their Habits
Darwin, Charles
Earthworms; Humification; Soils
Mr. Scott saw worm-castings on the lofty mountains of Sikkim in North
India. In South India Dr. King found in one place, on the plateau of the
Nilgiris, at an elevation of 7000 feet, “a good many castings,” which are
interesting for their great size. The worms which eject them are seen
only during the wet season, and are reported to be from 12 to 15 inches
in length, and as thick as a man’s little finger. These castings were
collected by Dr. King after a period of 110 days without any rain; and
they must have been ejected either during the north-east or more probably
during the previous south-west monsoon; for their surfaces had suffered
some disintegration and they were penetrated by many fine roots. A
drawing is here given (Fig. 4) of one which seems to have best retained
its original size and appearance. Notwithstanding some loss from
disintegration, five of the largest of these castings (after having been
well sun-dried) weighed each on an average 89.5 grammes, or above 3 oz.;
and the largest weighed 123.14 grammes, or 4⅓ oz.,—that is, above a
quarter of a pound! The largest convolutions were rather more than one
inch in diameter; but it is probable that they had subsided a little
whilst soft, and that their diameters had thus been increased. Some had
flowed so much that they now consisted of a pile of almost flat confluent
cakes. All were formed of fine, rather light-coloured earth, and were
surprisingly hard and compact, owing no doubt to the animal matter by
which the particles of earth had been cemented together. They did not
disintegrate, even when left for some hours in water. Although they had
been cast up on the surface of gravelly soil, they contained extremely
few bits of rock, the largest of which was only 0.15 inch in diameter.
Dr. King saw in Ceylon a worm about 2 feet in length and ½ inch in
diameter; and he was told that it was a very common species during the
wet season. These worms must throw up castings at least as large as
those on the Nilgiri Mountains; but Dr. King saw none during his short
visit to Ceylon.
Sufficient facts have now been given, showing that worms do much work in
bringing up fine earth to the surface in most or all parts of the world,
and under the most different climates.
CHAPTER III.
THE AMOUNT OF FINE EARTH BROUGHT UP BY WORMS TO THE SURFACE.
Rate at which various objects strewed on the surface of grass-fields are
covered up by the castings of worms—The burial of a paved path—The slow
subsidence of great stones left on the surface—The number of worms which
live within a given space—The weight of earth ejected from a burrow, and
from all the burrows within a given space—The thickness of the layer of
mould which the castings on a given space would form within a given time
if uniformly spread out—The slow rate at which mould can increase to a
great thickness—Conclusion.
Public-domain text, read in full here on John Shaqi.
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