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 fallen petioles of our native ash-tree were next observed, and the
rule with most objects, viz., that a large majority are dragged into the
burrows by the more pointed end, had not here been followed; and this
fact much surprised me at first. These petioles vary in length from 5 to
8½ inches; they are thick and fleshy towards the base, whence they taper
gently towards the apex, which is a little enlarged and truncated where
the terminal leaflet had been originally attached. Under some ash-trees
growing in a grass-field, 229 petioles were pulled out of worm burrows
early in January, and of these 51.5 per cent. had been drawn in by the
base, and 48.5 per cent. by the apex. This anomaly was however readily
explained as soon as the thick basal part was examined; for in 78 out of
103 petioles, this part had been gnawed by worms, just above the
horse-shoe shaped articulation. In most cases there could be no mistake
about the gnawing; for ungnawed petioles which were examined after being
exposed to the weather for eight additional weeks had not become more
disintegrated or decayed near the base than elsewhere. It is thus
evident that the thick basal end of the petiole is drawn in not solely
for the sake of plugging up the mouths of the burrows, but as food. Even
the narrow truncated tips of some few petioles had been gnawed; and this
was the case in 6 out of 37 which were examined for this purpose. Worms,
after having drawn in and gnawed the basal end, often push the petioles
out of their burrows; and then drag in fresh ones, either by the base for
food, or by the apex for plugging up the mouth more effectually. Thus,
out of 37 petioles inserted by their tips, 5 had been previously drawn in
by the base, for this part had been gnawed. Again, I collected a handful
of petioles lying loose on the ground close to some plugged-up burrows,
where the surface was thickly strewed with other petioles which
apparently had never been touched by worms; and 14 out of 47 (_i.e._
nearly one-third), after having had their bases gnawed had been pushed
out of the burrows and were now lying on the ground. From these several
facts we may conclude that worms draw in some petioles of the ash by the
base to serve as food, and others by the tip to plug up the mouths of
their burrows in the most efficient manner.
Public-domain text, read in full here on John Shaqi.
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