The Formation of Vegetable Mould(蔬菜为何发霉)

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THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
1
The Formation of
Vegetable Mould
Charles Darwin
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
2
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
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
3
Society of London, {2} "On the Formation of Mould," in which it was
shown that small fragments of burnt marl, cinders, &c., 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
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
4
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.
[FIRST EDITION, October 10th, 1881.]
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
5
CHAPTER I
HABITS OF WORMS.
HABITS OF WORMS.HABITS OF WORMS.
HABITS OF WORMS.
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.
Earth-worms are distributed throughout the world under the form of a
few genera, which externally are closely similar to one another. The
British species of Lumbricus have never been carefully monographed; but
we may judge of their probable number from those inhabiting
neighbouring countries. In Scandinavia there are eight species, according
to Eisen; {7} but two of these rarely burrow in the ground, and one
inhabits very wet places or even lives under the water. We are here
concerned only with the kinds which bring up earth to the surface in the
form of castings. Hoffmeister says that the species in Germany are not
well known, but gives the same number as Eisen, together with some
strongly marked varieties. {8}
Earth-worms abound in England in many different stations. Their
castings may be seen in extraordinary numbers on commons and chalk-
downs, so as almost to cover the whole surface, where the soil is poor and
the grass short and thin. But they are almost or quite as numerous in some
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
6
of the London parks, where the grass grows well and the soil appears rich.
Even on the same field worms are much more frequent in some places
than in others, without any visible difference in the nature of the soil. They
abound in paved court- yards close to houses; and an instance will be
given in which they had burrowed through the floor of a very damp cellar.
I have seen worms in black peat in a boggy field; but they are extremely
rare, or quite absent in the drier, brown, fibrous peat, which is so much
valued by gardeners. On dry, sandy or gravelly tracks, where heath with
some gorse, ferns, coarse grass, moss and lichens alone grow, hardly any
worms can be found. But in many parts of England, wherever a path
crosses a heath, its surface becomes covered with a fine short sward.
Whether this change of vegetation is due to the taller plants being killed
by the occasional trampling of man and animals, or to the soil being
occasionally manured by the droppings from animals, I do not know. {9}
On such grassy paths worm- castings may often be seen. On a heath in
Surrey, which was carefully examined, there were only a few castings on
these paths, where they were much inclined; but on the more level parts,
where a bed of fine earth had been washed down from the steeper parts
and had accumulated to a thickness of a few inches, worm-castings
abounded. These spots seemed to be overstocked with worms, so that they
had been compelled to spread to a distance of a few feet from the grassy
paths, and here their castings had been thrown up among the heath; but
beyond this limit, not a single casting could be found. A layer, though a
thin one, of fine earth, which probably long retains some moisture, is in all
cases, as I believe, necessary for their existence; and the mere
compression of the soil appears to be in some degree favourable to them,
for they often abound in old gravel walks, and in foot-paths across fields.
Beneath large trees few castings can be found during certain seasons
of the year, and this is apparently due to the moisture having been sucked
out of the ground by the innumerable roots of the trees; for such places
may be seen covered with castings after the heavy autumnal rains.
Although most coppices and woods support many worms, yet in a forest
of tall and ancient beech-trees in Knole Park, where the ground beneath
was bare of all vegetation, not a single casting could be found over wide
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
7
spaces, even during the autumn. Nevertheless, castings were abundant on
some grass- covered glades and indentations which penetrated this forest.
On the mountains of North Wales and on the Alps, worms, as I have been
informed, are in most places rare; and this may perhaps be due to the close
proximity of the subjacent rocks, into which worms cannot burrow during
the winter so as to escape being frozen. Dr. McIntosh, however, found
worm-castings at a height of 1500 feet on Schiehallion in Scotland. They
are numerous on some hills near Turin at from 2000 to 3000 feet above the
sea, and at a great altitude on the Nilgiri Mountains in South India and on
the Himalaya.
Earth-worms must be considered as terrestrial animals, though they are
still in one sense semi-aquatic, like the other members of the great class of
annelids to which they belong. M. Perrier found that their exposure to the
dry air of a room for only a single night was fatal to them. On the other
hand he kept several large worms alive for nearly four months, completely
submerged in water. {10} During the summer when the ground is dry, they
penetrate to a considerable depth and cease to work, as they do during the
winter when the ground is frozen. Worms are nocturnal in their habits, and
at night may be seen crawling about in large numbers, but usually with
their tails still inserted in their burrows. By the expansion of this part of
their bodies, and with the help of the short, slightly reflexed bristles, with
which their bodies are armed, they hold so fast that they can seldom be
dragged out of the ground without being torn into pieces. {11} During the
day they remain in their burrows, except at the pairing season, when those
which inhabit adjoining burrows expose the greater part of their bodies for
an hour or two in the early morning. Sick individuals, which are generally
affected by the parasitic larvae of a fly, must also be excepted, as they
wander about during the day and die on the surface. After heavy rain
succeeding dry weather, an astonishing number of dead worms may
sometimes be seen lying on the ground. Mr. Galton informs me that on
one such occasion (March, 1881), the dead worms averaged one for every
two and a half paces in length on a walk in Hyde Park, four paces in width.
He counted no less than 45 dead worms in one place in a length of sixteen
paces. From the facts above given, it is not probable that these worms
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
8
could have been drowned, and if they had been drowned they would have
perished in their burrows. I believe that they were already sick, and that
their deaths were merely hastened by the ground being flooded.
It has often been said that under ordinary circumstances healthy
worms never, or very rarely, completely leave their burrows at night; but
this is an error, as White of Selborne long ago knew. In the morning, after
there has been heavy rain, the film of mud or of very fine sand over
gravel-walks is often plainly marked with their tracks. I have noticed this
from August to May, both months included, and it probably occurs during
the two remaining months of the year when they are wet. On these
occasions, very few dead worms could anywhere be seen. On January 31,
1881, after a long- continued and unusually severe frost with much snow,
as soon as a thaw set in, the walks were marked with innumerable tracks.
On one occasion, five tracks were counted crossing a space of only an inch
square. They could sometimes be traced either to or from the mouths of
the burrows in the gravel-walks, for distances between 2 or 3 up to 15
yards. I have never seen two tracks leading to the same burrow; nor is it
likely, from what we shall presently see of their sense-organs, that a worm
could find its way back to its burrow after having once left it. They
apparently leave their burrows on a voyage of discovery, and thus they
find new sites to inhabit.
Morren states {12} that worms often lie for hours almost motionless
close beneath the mouths of their burrows. I have occasionally noticed the
same fact with worms kept in pots in the house; so that by looking down
into their burrows, their heads could just be seen. If the ejected earth or
rubbish over the burrows be suddenly removed, the end of the worm's
body may very often be seen rapidly retreating. This habit of lying near
the surface leads to their destruction to an immense extent. Every morning
during certain seasons of the year, the thrushes and blackbirds on all the
lawns throughout the country draw out of their holes an astonishing
number of worms, and this they could not do, unless they lay close to the
surface. It is not probable that worms behave in this manner for the sake of
breathing fresh air, for we have seen that they can live for a long time
under water. I believe that they lie near the surface for the sake of warmth,
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
9
especially in the morning; and we shall hereafter find that they often coat
the mouths of their burrows with leaves, apparently to prevent their bodies
from coming into close contact with the cold damp earth. It is said that
they completely close their burrows during the winter.
Structure.--A few remarks must be made on this subject. The body of a
large worm consists of from 100 to 200 almost cylindrical rings or
segments, each furnished with minute bristles. The muscular system is
well developed. Worms can crawl backwards as well as forwards, and by
the aid of their affixed tails can retreat with extraordinary rapidity into
their burrows. The mouth is situated at the anterior end of the body, and is
provided with a little projection (lobe or lip, as it has been variously called)
which is used for prehension. Internally, behind the mouth, there is a
strong pharynx, shown in the accompanying diagram (Fig. 1) which is
pushed forwards when the animal eats, and this part corresponds,
according to Perrier, with the protrudable trunk or proboscis of other
annelids. The pharynx leads into the oesophagus, on each side of which in
the lower part there are three pairs of large glands, which secrete a
surprising amount of carbonate of lime. These calciferous glands are
highly remarkable, for nothing like them is known in any other animal.
Their use will be discussed when we treat of the digestive process. In most
of the species, the oesophagus is enlarged into a crop in front of the
gizzard. This latter organ is lined with a smooth thick chitinous membrane,
and is surrounded by weak longitudinal, but powerful transverse muscles.
Perrier saw these muscles in energetic action; and, as he remarks, the
trituration of the food must be chiefly effected by this organ, for worms
possess no jaws or teeth of any kind. Grains of sand and small stones,
from the 1/20 to a little more than the 1/10 inch in diameter, may generally
be found in their gizzards and intestines. As it is certain that worms
swallow many little stones, independently of those swallowed while
excavating their burrows, it is probable that they serve, like mill-stones, to
triturate their food. The gizzard opens into the intestine, which runs in a
straight course to the vent at the posterior end of the body. The intestine
presents a remarkable structure, the typhlosolis, or, as the old anatomists
called it, an intestine within an intestine; and Claparede {13} has shown
THE FORMATION OF VEGETABLE MOULD THROUGH THE ACTION OF WORMS WITH OBSERVATIONS
ON THEIR HABITS.
10
that this consists of a deep longitudinal involution of the walls of the
intestine, by which means an extensive absorbent surface is gained.
The circulatory system is well developed. Worms breathe by their skin,
as they do not possess any special respiratory organs. The two sexes are
united in the same individual, but two individuals pair together. The
nervous system is fairly well developed; and the two almost confluent
cerebral ganglia are situated very near to the anterior end of the body.
Senses.--Worms are destitute of eyes, and at first I thought that they
were quite insensible to light; for those kept in confinement were
repeatedly observed by the aid of a candle, and others out of doors by the
aid of a lantern, yet they were rarely alarmed, although extremely timid
animals. Other persons have found no difficulty in observing worms at
night by the same means. {14}
Hoffmeister, however, states {15} that worms, with the exception of a
few individuals, are extremely sensitive to light; but he admits that in most
cases a certain time is requisite for its action. These statements led me to
watch on many successive nights worms kept in pots, which were
protected from currents of air by means of glass plates. The pots were
approached very gently, in order that no vibration of the floor should be
caused. When under these circumstances worms were illuminated by a
bull's-eye lantern having slides of dark red and blue glass, which
intercepted so much light that they could be seen only with some difficulty,
they were not at all affected by this amount of light, however long they
were exposed to it. The light, as far as I could judge, was brighter than that
from the full moon. Its colour apparently made no difference in the result.
When they were illuminated by a candle, or even by a bright paraffin lamp,
they were not usually affected at first. Nor were they when the light was
alternately admitted and shut off. Sometimes, however, they behaved very
differently, for as soon as the light fell on them, they withdrew into their
burrows with almost instantaneous rapidity. This occurred perhaps once
out of a dozen times. When they did not withdraw instantly, they often
raised the anterior tapering ends of their bodies from the ground, as if their
attention was aroused or as if surprise was felt; or they moved their bodies
from side to side as if feeling for some object. They appeared distressed by
摘要：

THEFORMATIONOFVEGETABLEMOULDTHROUGHTHEACTIONOFWORMSWITHOBSERVATIONSONTHEIRHABITS.1TheFormationofVegetableMouldCharlesDarwinTHEFORMATIONOFVEGETABLEMOULDTHROUGHTHEACTIONOFWORMSWITHOBSERVATIONSONTHEIRHABITS.2INTRODUCTION.Thesharewhichwormshavetakenintheformationofthelayerofvegetablemould,whichcoversthe...

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