the formation of vegetable mould-第1章

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The　Formation　of　Vegetable　Mould　through　the　action　of　worms　with
observations　of　their　habits

by　Charles　Darwin





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；　
&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　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。＇



CHAPTER　IHABITS　OF　WORMS。



Nature　of　the　sites　inhabitedCan　live　long　under　water
NocturnalWander　about　at　nightOften　lie　close　to　the　mouths　of　
their　burrows；　and　are　thus　destroyed　in　large　numbers　by　birds
StructureDo　not　possess　eyes；　but　can　distinguish　between　light　
and　darknessRetreat　rapidly　when　brightly　illuminated；　not　by　a　
reflex　actionPower　of　attentionSensitive　to　heat　and　cold
Completely　deafSensitive　to　vibrations　and　to　touchFeeble　power　
of　smellTasteMental　qualitiesNature　of　foodOmnivorous
DigestionLeaves　before　being　swallowed；　moistened　with　a　fluid　of　
the　nature　of　the　pancreatic　secretionExtra…stomachal　digestion
Calciferous　glands；　structure　ofCalcareous　concretions　formed　in　
the　anterior　pair　of　glandsThe　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　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　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。