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The Formation of
Vegetable Mould through the Action of Worms
with
Observations on their Habits
by Charles Darwin
First Edition, 10th
October, 1881
Reprint 2008
by Geraldine Murfin-Shaw
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Publisher's description : Paperback
book; 151 pages, 15.24 cm x 22.86 cm (6" x 9"), perfect
binding, cream interior paper (60# weight), black and white interior
ink, white exterior paper (100# weight), full colour exterior ink.
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CONTENTS
Introduction page 6
Chapter
1: Habits of Worms page
10
Nature of the sites inhabited Can live long under water
Nocturnal Wander about at night Often lie close to the mouths
of their burrows, and are thus destroyed in large numbers by birds
Structure Do not possess eyes, but can distinguish between light
and darkness Retreat rapidly when brightly illuminated, not by a
reflex action Power of attention Sensitive to heat and cold
Completely deaf Sensitive to vibrations and to touch
Feeble power of smell Taste Mental qualities Nature of
food Omnivorous Digestion Leaves before being swallowed,
moistened with a fluid of the nature of the pancreatic secretion
Extra-stomachal digestion Calciferous glands, structure of
Calcareous concretions formed in the anterior pair of glands The
calcareous matter primarily an excretion, but secondarily serves to
neutralise the acids generated during the digestive process.
Chapter
2: Habits of Worms - continued page
31
Manner in which worms seize objects Their power of suction
The instinct of plugging up the mouths of their burrows Stones
piled over the burrows The advantages thus gained
Intelligence shown by worms in their manner of plugging up their
burrows Various kinds of leaves and other objects thus usedTriangles
of paper Summary of reasons for believing that worms exhibit
some intelligence Means by which they excavate their burrows, by
pushing away the earth and swallowing it Earth also swallowed
for the nutritious matter which it contains Depth to which worms
burrow, and the construction of their burrows Burrows lined with
castings, and in the upper part with leaves The lowest part
paved with little stones or seeds Manner in which the castings
are ejected The collapse of old burrows Distribution of
worms Tower-like castings in Bengal Gigantic castings on the
Nilgiri Mountains Castings ejected in all countries.
Chapter
3: The Amount of Fine Earth Brought Up by Worms to the Surface page 63
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
Chapter
4: The Part which Worms have Played in the Burial of Ancient Buildings
page 84
The accumulation of rubbish on the sites of great cities independent
of the action of worms The burial of a Roman villa at Abinger
The floors and walls penetrated by worms Subsidence of a
modern pavement The buried pavement at Beaulieu Abbey Roman
villas at Chedworth and Brading The remains of the Roman town at
Silchester The nature of the debris by which the remains are
covered The penetration of the tesselated floors and walls by
wormsSubsidence of the floors Thickness of the mould The
old Roman city of Wroxeter Thickness of the mould Depth of
the foundations of some of the Buildings Conclusion
Chapter
5: The Action of Worms in the Denudation of the Land page
106
Evidence of the amount of denudation which the land has undergone
Sub-aerial denudation The deposition of dust Vegetable mould,
its dark colour and fine texture largely due to the action of worms
The disintegration of rocks by the humus-acids Similar acids
apparently generated within the bodies of worms The action of
these acids facilitated by the continued movement of the particles of
earth A thick bed of mould checks the disintegration of the
underlying soil and rocks. Particles of stone worn or triturated in
the gizzards of worms Swallowed stones serve as mill-stones
The levigated state of the castings Fragments of brick in the
castings over ancient buildings well rounded. The triturating power of
worms not quite insignificant under a geological point of view
Chapter
6: The Denudation of the Land - continued
page 118
Denudation aided by recently ejected castings flowing
down inclined grass-covered surfaces The amount of earth which
annually flows downwards The effect of tropical rain on worm
castings The finest particles of earth washed completely away from
castings The disintegration of dried castings into pellets, and
their rolling down inclined surfaces The formation of little ledges
on hill-sides, in part due to the accumulation of disintegrated castings
Castings blown to leeward over level land An attempt to estimate
the amount thus blown The degradation of ancient encampments and
tumuli The preservation of the crowns and furrows on land anciently
ploughed The formation and amount of mould over the Chalk formation.
Chapter
7: Conclusion page
138
Summary of the part which worms have played in the
history of the world Their aid in the disintegration of rocks
In the denudation of the land In the preservation of ancient
remains In the preparation of the soil for the growth of plants
Mental powers of worms Conclusion
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Introduction
The share which worms have taken in the formation of
the layer of vegetable mould, which covers the whole surface of the land
in every moderately humid country, is the subject of the present volume.
This mould is generally of a blackish colour and a few inches in
thickness. In different districts it differs but little in appearance,
although it may rest on various subsoils. The uniform fineness of the
particles of which it is composed is one of its chief characteristic
features; and this may be well observed in any gravelly country, where a
recently-ploughed field immediately adjoins one which has long remained
undisturbed for pasture, and where the vegetable mould is exposed on the
sides of a ditch or hole. The subject may appear an insignificant one,
but we shall see that it possesses some interest; and the maxim "de
minimis non curat lex," does not apply to science. Even Elie de
Beaumont, who generally undervalues small agencies and their accumulated
effects, remarks: [ 1]
"La couche tres-mince de la terre vegetale est un monument d'une
haute antiquite, et, par le fait de sa permanence, un objet digne
d'occuper le geologue, et capable de lui fournir des remarques
interessantes." Although the superficial layer of vegetable mould
as a whole no doubt is of the highest antiquity, yet in regard to its
permanence, we shall hereafter see reason to believe that its component
particles are in most cases removed at not a very slow rate, and are
replaced by others due to the disintegration of the underlying
materials.
As I was led to keep in my study during many months
worms in pots filled with earth, I became interested in them, and wished
to learn how far they acted consciously, and how much mental power they
displayed. I was the more desirous to learn something on this head, as
few observations of this kind have been made, as far as I know, on
animals so low in the scale of organization and so poorly provided with
sense-organs, as are earth-worms.
In the year 1837, a short paper was read by me before
the Geological Society of London, [ 2]
"On the Formation of Mould," in which it was shown that small
fragments of burnt marl, cinders, which had been thickly strewed over
the surface of several meadows, were found after a few years lying at
the depth of some inches beneath the turf, but still forming a layer.
This apparent sinking of superficial bodies is due, as was first
suggested to me by Mr. Wedgwood of Maer Hall in Staffordshire, to the
large quantity of fine earth continually brought up to the surface by
worms in the form of castings. These castings are sooner or later spread
out and cover up any object left on the surface. I was thus led to
conclude that all the vegetable mould over the whole country has passed
many times through, and will again pass many times through, the
intestinal canals of worms. Hence the term "animal mould"
would be in some respects more appropriate than that commonly used of
"vegetable mould."
Ten years after the publication of my paper, M.
D'Archiac, evidently influenced by the doctrines of Elie de Beaumont,
wrote about my "singuliere theorie," and objected that it
could apply only to "les prairies basses et humides;" and that
"les terres labourees, les bois, les prairies elevees, n'apportent
aucune preuve a l'appui de cette maniere de voir." [ 3]
But M. D'Archiac must have thus argued from inner consciousness and not
from observation, for worms abound to an extraordinary degree in kitchen
gardens where the soil is continually worked, though in such loose soil
they generally deposit their castings in any open cavities or within
their old burrows instead of on the surface. Hensen estimates that there
are about twice as many worms in gardens as in corn-fields. [4]
With respect to "prairies elevees," I do not know how it may
be in France, but nowhere in England have I seen the ground so thickly
covered with castings as on commons, at a height of several hundred feet
above the sea. In woods again, if the loose leaves in autumn are
removed, the whole surface will be found strewed with castings. Dr.
King, the superintendent of the Botanic Garden in Calcutta, to whose
kindness I am indebted for many observations on earth-worms, informs me
that he found, near Nancy in France, the bottom of the State forests
covered over many acres with a spongy layer, composed of dead leaves and
innumerable worm- castings. He there heard the Professor of "Amenagement
des Forets" lecturing to his pupils, and pointing out this case as
a "beautiful example of the natural cultivation of the soil; for
year after year the thrown-up castings cover the dead leaves; the result
being a rich humus of great thickness."
In the year 1869, Mr. Fish [ 5]
rejected my conclusions with respect to the part which worms have played
in the formation of vegetable mould, merely on account of their assumed
incapacity to do so much work. He remarks that "considering their
weakness and their size, the work they are represented to have
accomplished is stupendous." Here we have an instance of that
inability to sum up the effects of a continually recurrent cause, which
has often retarded the progress of science, as formerly in the case of
geology, and more recently in that of the principle of evolution.
Although these several objections seemed to me to
have no weight, yet I resolved to make more observations of the same
kind as those published, and to attack the problem on another side;
namely, to weigh all the castings thrown up within a given time in a
measured space, instead of ascertaining the rate at which objects left
on the surface were buried by worms. But some of my observations have
been rendered almost superfluous by an admirable paper by Hensen,
already alluded to, which appeared in 1877. [ 6]
Before entering on details with respect to the castings, it will be
advisable to give some account of the habits of worms from my own
observations and from those of other naturalists. |
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