the formation of vegetable mould-第22章
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nature of the substratum； which at Leith Hill Place was sandy soil
including many bits of rock； and at Stonehenge； chalk…rubble with
broken flints； considering； also； the presence of the turf…covered
sloping border of mould round the great fragments of stone at both
these places； their sinking does not appear to have been sensibly
aided by their weight； though this was considerable。 ｛50｝
On the number of worms which live within a given space。We will
now show； firstly； what a vast number of worms live unseen by us
beneath our feet； and； secondly； the actual weight of the earth
which they bring up to the surface within a given space and within
a given time。 Hensen； who has published so full and interesting an
account of the habits of worms； ｛51｝ calculates； from the number
which he found in a measured space； that there must exist 133；000
living worms in a hectare of land； or 53；767 in an acre。 This
latter number of worms would weigh 356 pounds； taking Hensen's
standard of the weight of a single worm； namely； three grams。 It
should； however； be noted that this calculation is founded on the
numbers found in a garden； and Hensen believes that worms are here
twice as numerous as in corn…fields。 The above result； astonishing
though it be； seems to me credible； judging from the number of
worms which I have sometimes seen； and from the number daily
destroyed by birds without the species being exterminated。 Some
barrels of bad ale were left on Mr。 Miller's land； ｛52｝ in the hope
of making vinegar； but the vinegar proved bad； and the barrels were
upset。 It should be premised that acetic acid is so deadly a
poison to worms that Perrier found that a glass rod dipped into
this acid and then into a considerable body of water in which worms
were immersed； invariably killed them quickly。 On the morning
after the barrels had been upset； 〃the heaps of worms which lay
dead on the ground were so amazing； that if Mr。 Miller had not seen
them； he could not have thought it possible for such numbers to
have existed in the space。〃 As further evidence of the large
number of worms which live in the ground； Hensen states that he
found in a garden sixty…four open burrows in a space of 14。5 square
feet； that is； nine in 2 square feet。 But the burrows are
sometimes much more numerous； for when digging in a grass…field
near Maer Hall； I found a cake of dry earth； as large as my two
open hands； which was penetrated by seven burrows； as large as
goose…quills。
Weight of the earth ejected from a single burrow； and from all the
burrows within a given space。With respect to the weight of the
earth daily ejected by worms； Hensen found that it amounted； in the
case of some worms which he kept in confinement； and which he
appears to have fed with leaves； to only 0。5 gram； or less than 8
grains per diem。 But a very much larger amount must be ejected by
worms in their natural state； at the periods when they consume
earth as food instead of leaves； and when they are making deep
burrows。 This is rendered almost certain by the following weights
of the castings thrown up at the mouths of single burrows； the
whole of which appeared to have been ejected within no long time；
as was certainly the case in several instances。 The castings were
dried （excepting in one specified instance） by exposure during many
days to the sun or before a hot fire。
WEIGHT OF THE CASTINGS ACCUMULATED AT THE MOUTH OF A SINGLE BURROW。
（Weight in ounces given in parenthesisDP。）
（1。） Down； Kent （sub…soil red clay； full of flints； over…lying the
chalk）。 The largest casting which I could find on the flanks of a
steep valley； the sub…soil being here shallow。 In this one case；
the casting was not well dried （3。98）
（2。） Down。Largest casting which I could find （consisting chiefly
of calcareous matter）； on extremely poor pasture land at the bottom
of the valley mentioned under （1。） （3。87）
（3。） Down。A large casting； but not of unusual size； from a
nearly level field； poor pasture； laid down in a grass about 35
years before （1。22）
（4。） Down。 Average weight of 11 not large castings ejected on a
sloping surface on my lawn； after they had suffered some loss of
weight from being exposed during a considerable length of time to
rain （0。7）
（5。） Near Nice in France。Average weight of 12 castings of
ordinary dimensions； collected by Dr。 King on land which had not
been mown for a long time and where worms abounded； viz。； a lawn
protected by shrubberies near the sea； soil sandy and calcareous；
these castings had been exposed for some time to rain； before being
collected； and must have lost some weight by disintegration； but
they still retained their form （1。37）
（6。） The heaviest of the above twelve castings （1。76）
（7。） Lower Bengal。Average weight of 22 castings； collected by
Mr。 J。 Scott； and stated by him to have been thrown up in the
course of one or two nights （1。24）
（8。） The heaviest of the above 22 castings （2。09）
（9。） Nilgiri Mountains； S。 India； average weight of the 5 largest
castings collected by Dr。 King。 They had been exposed to the rain
of the last monsoon； and must have lost some weight （3。15）
（10。） The heaviest of the above 5 castings （4。34）
In this table we see that castings which had been ejected at the
mouth of the same burrow； and which in most cases appeared fresh
and always retained their vermiform configuration； generally
exceeded an ounce in weight after being dried； and sometimes nearly
equalled a quarter of a pound。 On the Nilgiri mountains one
casting even exceeded this latter weight。 The largest castings in
England were found on extremely poor pasture…land； and these； as
far as I have seen； are generally larger than those on land
producing a rich vegetation。 It would appear that worms have to
swallow a greater amount of earth on poor than on rich land； in
order to obtain sufficient nutriment。
With respect to the tower…like castings near Nice （Nos。 5 and 6 in
the above table）； Dr。 King often found five or six of them on a
square foot of surface； and these； judging from their average
weight； would have weighed together 7。5 ounces； so that the weight
of those on a square yard would have been 4 lb。 3。5 oz。 Dr。 King
collected； near the close of the year 1872； all the castings which
still retained their vermiform shape； whether broken down or not；
from a square foot； in a place abounding with worms； on the summit
of a bank； where no castings could have rolled down from above。
These castings must have been ejected； as he judged from their
appearance in reference to the rainy and dry periods near Nice；
within the previous five or six months； they weighed 9。5 oz。； or 5
lb。 5。5 oz。 per square yard。 After an interval of four months； Dr。
King collected all the castings subsequently ejected on the same
square foot of surface； and they weighed 2。5 oz。； or 1 lb。 6。5 oz。
per square yard。 Therefore within about ten months； or we will say
for safety's sake within a year； 12 oz。 of castings were thrown up
on this one square foot； or 6。75 pounds on the square yard； and
this would give 14。58 tons per acre。
In a field at the bottom of a valley in the chalk （see No。 2 in the
foregoing table）； a square yard was measured at a spot where very
large castings abounded； they appeared； however； almost equally
numerous in a few other places。 These castings； which retained
perfectly their vermiform shape； were collected； and they weighed
when partially dried； 1 lb。 13。5 oz。 This field had been rolled
with a heavy agricultural roller fifty…two days before； and this
would certainly have flattened every single casting on the land。
The weather had been very dry for two or three weeks before the day
of collection； so that not one casting appeared fresh or had been
recently ejected。 We may therefore assume that those which were
weighed had been ejected within； we will say； forty days from the
time when the field was rolled；that is； twelve days short of the
whole intervening period。 I had examined the same part of the
field shortly
