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
The observations on which these several statements are founded must now
be given in some detail. Castings when first ejected are viscid and
soft; during rain, at which time worms apparently prefer to eject them,
they are still softer; so that I have sometimes thought that worms must
swallow much water at such times. However this may be, rain, even when
not very heavy, if long continued, renders recently-ejected castings
semi-fluid; and on level ground they then spread out into thin, circular,
flat discs, exactly as would so much honey or very soft mortar, with all
traces of their vermiform structure lost. This latter fact was sometimes
made evident, when a worm had subsequently bored through a flat circular
disc of this kind, and heaped up a fresh vermiform mass in the centre.
These flat subsided discs have been repeatedly seen by me after heavy
rain, in many places on land of all kinds.
_On the flowing of wet castings_, _and the rolling of dry disintegrated
castings down inclined surfaces_.—When castings are ejected on an
inclined surface during or shortly before heavy rain, they cannot fail to
flow a little down the slope. Thus, on some steep slopes in Knole Park,
which were covered with coarse grass and had apparently existed in this
state from time immemorial, I found (Oct. 22, 1872) after several wet
days that almost all the many castings were considerably elongated in the
line of the slope; and that they now consisted of smooth, only slightly
conical masses. Whenever the mouths of the burrows could be found from
which the earth had been ejected, there was more earth below than above
them. After some heavy storms of rain (Jan. 25, 1872) two rather steeply
inclined fields near Down, which had formerly been ploughed and were now
rather sparsely clothed with poor grass, were visited, and many castings
extended down the slopes for a length of 5 inches, which was twice or
thrice the usual diameter of the castings thrown up on the level parts of
these same fields. On some fine grassy slopes in Holwood Park, inclined
at angles between 8° and 11° 30′ with the horizon, where the surface
apparently had never been disturbed by the hand of man, castings abounded
in extraordinary numbers: and a space 16 inches in length transversely to
the slope and 6 inches in the line of the slope, was completely coated,
between the blades of grass, with a uniform sheet of confluent and
subsided castings. Here also in many places the castings had flowed down
the slope, and now formed smooth narrow patches of earth, 6, 7, and 7½
inches in length. Some of these consisted of two castings, one above the
other, which had become so completely confluent that they could hardly be
distinguished. On my lawn, clothed with very fine grass, most of the
castings are black, but some are yellowish from earth having been brought
up from a greater depth than usual, and the flowing-down of these yellow
castings after heavy rain, could be clearly seen where the slope was 5°;
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