THE POWER OF MOVEMENT IN PLANTS, DARWIN

vm CONTENTS.: leaflets close whenplantkept very dry—Trop^olum: leaves dc modesofsleeping—Melilotus: singular movemenrs of terminal leaflet—Trifolium—Desmodiura: rudimentary lateral leafl

77 1

3 ^7 1^(Authorized Edition

CHAPTER I.

The ClKOtTMNUTATING MOVEMENTS OF SbBDLING PLANTS

thegroundandstraighteningitself,andwhenerect—

Avena,Nephrodium, and Selaginella 10-66'

CHAPTEE II

Seedling Plants

ground—Manner inwhich hypocotyls and other organs break

—

VI CONTENTS.

whenerect—Circumnutationof cotyledons—Pulvini or joints of

Mannerinwhichradicles bendwhentheyencounteranobstacle in

—

Power of discriminatingbetween objects attached on opposite

sides—Tips of secondary radicles sensitive—Pisum, tips of

radicles sensitive—^Effects of such sensitiveness in overcoming

sensitive to caustic—Quercus,tip highlysensitive to contact

—

Power of discrimination—Zea, tip highly sensitive, secondary

radicles—Sensitiveness of radicles to moist air— Summary of

CHAPTEE IV.

The CiROUMNnTATiNG Movements op the several parts of

Mature Plants

CONTENTS. ^11

CHAPTER V

Modified Cibcuhndtation: Climbing Plants; Epinastio and

Hyponastio Movements.

growthofyoung leaves—Hyponastio growth of thehypocotyls

—

CHAPTEE VI.

Modified Cieodmnutation: Sleep or Nyctitkopic Movkmexts,

THEIR Use: Sleep of Cotyledons

and onthe cotyledonsofMimosa—Concludingremarks on

—

CHAPTER VII.

MouiFiED Ciecumnutation: Nyctitkopic or Sleep Movements

OF Leaves

—

vm CONTENTS.

:

leaflets close whenplantkept very dry—Trop^olum: leaves dc

modesofsleeping—Melilotus: singular movemenrs of terminal

leaflet—Trifolium—Desmodiura: rudimentary lateral leaflets,

movements of,not developed on young plants, state of their

move-ments of leaves, effect of darkness—Mimosa albida, reduced

leaflets of—Schranlda: downward movement of the pinnse

—

CHAPTEE VIII.

Modified Circumsutation: Movemekts excited by Light

So-called diurnal sleep—Chlorophyll injured by intense light

—

Movementstoavoid intense light 418-448

CHAPTEE IX.

helic-tropic— Sameorganheliotropic atone age andnotatanother

—

CONTENTS. IS

of lightdonotcorrespond withitsintensity—Ettccts ofprevioui.

illumination— Timerequiredforthe action of light—After-effects

with which plants benfl to the light—This dependent on the

mannerofbending—Results of the exclusion of lightfromtheir

—

CHAPTEE X.

Modified Cikcumndtation: Movements excited by

Gravitation

Means of observation—Apogeotropism—Cytisus—Verbena—Beta

—Apogeotropismretardedbyheliotropism—Effectedbythe aid

—

CHAPTEE XL

Localised Bemsitiveness to Gravitation,anditsTbansmittbs

Effects

Greneral considerations—Viciafaba,effects ofamputatingthetips of

eativum, tips of radicles cauterised transversely, and on theii

sensibility to geotropism being localised in the tips of the

radicles Page 23-545

CHAPTEE XIL

seed— The radicle first protrudes and circumnutates—^Its tip

radicleactslikea brain 546-573

THE MOVEMENTS OF PLANTS.

INTRODUCTION.

The chief object of the present work is to describe'

move-ment, commontoalmost all plants The most widely

as»that of the stem of a climbing plant,which bends^successively toallpoints of the compass, so that the-tip revolves This movement has been called by

.much more convenientto use the termscircwnnutation

and circumnutate As we shall have to say much, about this movement, itwill be useful here briefly to

describe its nature If we observe a circumnutating

bend more and more easterly, until itfacesthe east;:

and so onwards to the south, then to the west, and'

or rather, as the stem is always growing upwards, a

circular spiral But it generally describes irregular

point-ing in any one direction, commonly moves back

axes directed to different points of tlie comjtass.Wliilst describing such figures,the apex often travels

generally narrow.

move-ments was believed to be due tothe increased growth

ofthe side which becomesfor a time convex; thatthis

a previously increased state of turgescence on the

so-called joint, cushion or pulvinus, which consists of

increase in size from a very early age,we meet with

similar movements; and here, as Pfeffer has shownf

the increased turgescence of the cells on opposite

deniesin certain cases the accuracy of DeVries' clusion about turgescence, and maintains| that the

con-increased extensibility of the cell-walls is the more

accompanyincreasedturgescenceinorderthatthepartmay bend is manifest,andthis has been insisted on by

several botanists; butin the case ofunicellular plants

buch,' &o., 4th edit p. 452) the f 'DiePeriodischcn

jreased growth, first ow one side and then on another,

is a seoondiiry effect, and that the increased

of their walls,isthe primary cause ofthemovement ofcircumnutation.*

broken through the ground, as well as their buried

pre-sent movement we have the basis or groundwork for

plant, of the most diversified movements Thus, thegreat sweeps made by the stems of twining plants,

and by the tendrils of other climbers, result from

a mere increase in the amplitude of the ordinary

movement of circumnutation The position which

young leaves and other organs ultimately assume

various plants are said to sleep at night, and it will

be seen that their blades then assume a verticalposition through modified circumnutation, in order

to protect their upper surfaces from being chilled

through radiation The movements of various organs

or transversely with respect to it, are all modified

oon-1 43,1878)onthis intricate subjeot sistingofa singlerowofoells,.aro

Hofmeister'a observatinns ('jah- yuluable in relationto this subjt.'Ct.

forms of circumnutation; as agaiu are the equally

prevalent movements of stems,&c., towards the zenith,

and of roots towards the centre of the earth In

it might have beenasked, how did all theirdiversified

movementsfor themost different purposes firstarise?

As the case stands, we know that there is always

movement in progress, and its amplitude, or

stimuli

The two which have interestedus mostare,firstly, thefact that with some seedling plants the uppermost

there-fore the upper part be wholly protected from light,

excited by light Secondly, with theradicles of

transmits an influence to the upperpart, causing itto

bend from the pressed side On the other hand, if

the tip is subjected to thevapourof water proceeding

totheattraction ofgravity,and bytransmission causes

centre oftheearth These several cases ofthe effects

contact, other vapour, and

INTKODUCTION. 5attraction of gravity being transmitted from the ex-cited part for some littledistance along the organ inquestion, have an important bearing on the theoryofallsuch movements.

supportsthecotyledons(i.e.the organswhichrepresent thefirst

fromthehypocotyl onlybythe presence of root-hairs and the

employ heliotropism and geotropism, &c., as the cause of the

thattheuppersurfaceof an organ growsmorequicklythanthe

lower surface,and thus causes it to bend downwards

Methods of Observation.— The movements, sometimes very

manytrialswefoundto be best,andwhichmust be described

might require, and were covered above by a large horizontal

cardwith ablack dotwasfixedtoastickdriveninto theground

Theweightof the filamentwas so slightthatevensmaUleaves

on the card were viewed through the horizontal or vertical

after-wards joined bystraight lines. The figures thus tracedwere

wasthesoledifficulty,and required some practice Norcould

Inanimate object which was made to s5ide along a straight

added thatwhen the dot on the cardwas placed half-an-inch

below or behind the bead of sealing-wax,andwhen the

times

been verydifficultto have ascertained in each case howgreat

the above methods, they were copied on tracing paper and

movement The nocturnal courses are representedbystraight

broken lines. The first dot is always made larger than the

5 INTKODUCTIOX.

forusbyMr George Darwin

been a much better plan to have used hemispherical glasses,

toany onewhowishestoknowthe exact amountofmovement,

In thefollowing chapters, the movements of a siderable number of plants are described; and the

con-species have been arranged according to the system

save the reader trouble, the conclusions and most of

of the whole volume; and he will thus see what

points interest him, and on which he requires thefullevidence

Finally, we must have the pleasure of

sincere thanks to SirJoseph Hooker and to Mr W.

sending us plants from Kew, butinprocuring others

from several sources when they were required for our

observations; also,fornaming manyspecies,and giving

10 OIBCUMNUTATION OF

The Cirocmnutatinq Movementsof Seedlixo Plahts

hypo-cotylwhilststillburiedbeneath thegroaiid,whiLtrisingabovethe

Nephro-dium,andSelaginella.

The following chapter is dcToted to the

sleep at night

was surrounded by little bits of wet sponge, and the

during sixty hours In this time the radicle increased in

firstclose to the apex ofthe radicle,andif it could have mained the time, themovement

re-beenmuchgreater, for atthecloseof our observations the tip,

roughlyascertainby

trac-ingshowsthat the basal part

circunmutateirregularly

dur-ing the whole time The

was magnified by the

fila-ment,which wasnearlyIinch

Anotherseed wastreatedandobserved in the samemanner,

Brassca oUriacea: circumnutationof radicle,tracedon horizontalglass,

Feb. 2nd Movement ofbead at

40times.

Fig 2.

,^^v^-Brassioaoleracea : circumnutating and geotropicmovementof radicle,

tracedon horizontalglassduring46hours.

was aflEtxedclose to its base The tracing (Kg 2,reduced by

CIECUMNUTATION OF

manner Fromtheradiclenot being quite perpendicularwhen

sometimes on another side. Occasionally the bead remained

firstverylittle affectedbygeotropism Filamentswereaffixed

move-mentsoftheradiclesof other plants,that theymaybelargelytrusted

stillenclosed within the seed In whatever position the seed

oreven earlier,the inner orconcavesurface of thearchgrows

from a considerable depth; and now the hypocotyl quickly

sur-rounding soil will permit; but this was difficult to observe,

wouldnaturallyhave reachedthesurface Seedswereallowed

togerminate on the surfaceof dampearth,andaftertheyhad

Chap I. BEASSICA 13

showing lateral movement, the arch must have been

Fig 3.

Brassica oleracea ; circumnutating movementofburied and arched cotyl(dimly illuminated fromabove), tracedonhorizontal glassduring

liypo-45 hours. Movementofbead of Slanient magnified about 25 times,

andherereducedtoone-halfof original scale.

were still almost completely enclosed within themuch-cracked

beneath the pressed-down earth, but the upper part of the

ago to circumnutate irregularly On the first daythe greatei

bowingoccurred,the chiefmovement wouldhave been atright

dragged frombeneath theground ontheeveningofthesecondday

Brassica oleracea : circumnutating movementofburiedand arched

hypo-cotyl,with thetwolegs ofthearchtied together, tracedonhorizontal glass during33Jhours. Movementof thebeadof filamentmagnifiedabout 26times,and here redu:ed toone-halforiginal scale.

from beginningtoseparateatonce,they weretiedtogetherwith

finesilk. Thiswasdone partlybecausewewishedtoascertain

to move,and whether the movement when not masked and

the 24th thearched hypocotyl sometimes remained stationary

having been tied, had grown broad and almost flat. The

Fig b.

Brassica oleracea: cii'cumLutatingmovementofthecrownofa buried anUarched hypocotyl,with the two legs tied together,tracedon a hori-

zontal glassduring 23hours. Movementof the beadof the filament

scale.

almostcompletely ceasedtomove

beneath the ground,andthehypocotyl has straightened itself

bygrowthalong the inner orconcavesurface,thereisnothingto

16 CIECUMNUTATION OF SEEDLINGS

whole daj so as to accommodate itself to the light On the

Ter-tieal glass Atfirst the plant bent so much towardsthelight

Fig 6.

Bradsicaoleracen; conjointcircumnutationof thehypoootyl and cotyledon?during10hours45 minutes Figure here reducedtoone-halforiginal

scale,

at5.30p!m.,and thecourseduringthisinterval of 1 h 30m hasbeen filled up byimagination,but cannot befar from correct

coty-ledon on the sidefurthest from the window Moreover, the

Brxssicaoleracea : conjointcircumnutation of the hypocotyl andcotyledons,

on avertical glass.

next 12 hours thebead swept obliquelyup and down8 times

second day the same cotyledon had

CIKCUMNUTATION OF SEBPLINGS. Chap.

beguntofall,and adotwas madeon afresh glass The

8hoursthebeadchanged

shown

wished to ascertain

Filaments were therefore

morn-ing, upto about11 A.M., they moved in zigzag lines towards

through apogeotropism After about 11 a.m they moved a

little back fromthe light,often crossing andrecrossing their

8.52A.M.,when thefirstdotwasmade,till10.55 a.m.; itthenrose

till9.23P.M.,when it made another loop,and at10.30p.m.was

show

Brassica oleracea : conjointcircumnutation

ofthehypocotyl anilcotyledonsduring

8 hiiurs. Figure here reduced to

one-third of yie original scale, as tracedena

vertical glass.

Thecabbage was oneofthefirstplants,the seedlings ofwhich

did not then know how far '^'

the circumnutation of the

by light. Young seedlings

minute or two during each

above them Duringthefirst

changed its course 13 times

same manner, but it was

complex one, though the

to the midrib ofoneof the

Itshould be noted that the chiefmovement of the cotyledons,

namely, up anddown,wouldbe shown on a horizontal

hypocotyl,in darkness, traced on a horizontal glass,by meansof a fila-

one-half oforiginal scale.

20 CIEOUMNUTATION OP

Fig 10.

up and down, asKg.10lierestands)being alittlelengthened

plane

with amicrometer eye-piece soadjusted

Brassicaoleracoa :

cotyledon,the

hypo-cotyl having been

secured to a sticlc,

traoed on a

horizon-tal glass, in

dark-ness,from 8.15 A.M.

the filament

magni-fied13times.

througha solution ofbichromateof

back-wards andforwardstothe extent of-j^gandsometimesof nearly

remarkable factwas the oscillatorymovement above described,

was exposed

twoor threeminuteswhilstaglassfilamentwaffixed vertically

tothehypocotyl; itwasthenagain placedindarkness for half

bichromate of potassium The point, oscillating as usual,

1m 30s. Theseedlingwasthen left indarkness for an hour,

15m 30s.to have crossed five divisions Another seedling,

roomwith a verydulllight,and left in complete darkness for

towards the light, as might have been expected, it travelledonlyat the rate of 12m 30s. for five divisions Itwas then

3m 18s.for five divisions

circumnutation, also, of the leaves of fully-developed plants

Fig 11.

Bithago segetum: ciruumnutation of hypocotyl, traced on » horUont&l

glass,bymeansofafilamentfixedtransverselyacross itssummit,from

filament magnified about 13times,herereducedtoone-halfthe original

scale.

22 CIECUMNUTATION OF

We endeavoured to observe the circumnutation ofthe

^'S- 12.

Oossypium (var Nankin cotton)

Qo^siipium ciicuinnn- the movementwas somuch exaggerated

tation of hypocotyl,

^j^^^^.^^^^^^^^^j^g g^f^^^^.jj^g^^^^f

tracedon ahorizon- ^

ijiix

tal glass,from 10.30 View. Itwas,however,manifest thattwo

A.M to 9.30A.M.on somewhatirregular ellipses were nearly

rwTceT'sSgiUu- ^1^°^t,ythefewdots.inKg.12,andthe

about the circumnutation of the hypocotyl, which described

sizes.

thewhole day, and as theyoffer the unusual case of moving

OflAp I. GOSSYPIUM 23

ofpaper having beenfixed to one ofthe cotyledons, its

pastmidnightitwasfound a little lower and somewhattoone

thewhole of the following day andnight ofJune22nd The

ascending and descending linestraced during the three days

were found hanging so nearlyverticallydown, thattheymight

asitremainednearly horizontal; butin thecourse of thedayit

CIKCUMNUTATION OF SEEDLINGS.

morn-ing; and wesee that during tho

inanhourortwodepended

morning (18th) both cotyledons

Their movementwastraced

down-wards; and at about 4 p.m the

move-mentcommenced

Another seedlingwasobserved

24h.,but withthedifferencethat

ismerelya great increaseofone

VMiviana.—

8'aO'a.m

u

Jxalis roeea: circumnutation of

cotyledons, thehypocotyl being

secured to a stick ;

illumina-ted from above. Figure hero

givenone-half of original scale.

Chap I. OXALIS 25

case of 0 rosea. A glass filament was fixed to a cotyledon,

Oxalis rosea : conjointcircumnutation of

A.M 19th. Theapex of the cotyledon

stoodonly3}inches fromthevertical

glass. Figure here given one-half of

original scale.

Oxalis Valdiviana : conjoint

circumnutation of a

cotyle-donandthe hypocotyl,traced

onvertical glass,during 24

hours. Figure here givenone-half of original scale seedling illuminated fromabove

the first daythe seedlingwas placed too far fromthevertical

grlasa j s thatthe tracingwas enormouslyexaggeratedandthe

26 CIROUMNUTATZON OF SEEDLINGS. Chap L

having from someunknown cause temporarily bent totheleft

behind the two now closedand vertical cotyledons; and the

in extent Therefore Pig.15 representsfairlywell the

move-ments of the cotyledons alone, with the exception of the one

re-markable fromthe amplitudeandrapidity oftheirmovements

beneath thehorizonwere measured at short intervals oftime

'

through 180°inunder 2h Wehavemetwithnoother instance

ofa ciroumnutatingmovementofsuchgreatamplitudeas180°

The

Chap I. TKOP^OLUM.

Fig 16.

evening

removing thesoilaburiedepicotyl

or plumule was found, with its

ofthecabbagepreviously described

or leg, just above the hypogean

surrounded by loose earth The

line. Thisgreatmovement, dueto

occurred with the hypocotyl of

arched epicotyl wasobserved in the same manner, excepting

forthesakeof preventing the great movement justmentioned

It moved, however, in the evening in the same direction as

circum-nutatioa of buried and arched

epicotyl, tracedon a

horizon-tal glass, from 9.20 A.M to

8.15p.m. MoTementofbead

times.

28 CIECUMNUTATION OF

arehypogean Thecircumnutationofanepiootyl,whichatthe

abovetheground, isshown in the annexed figure (Fig 17),as

Fig J7.

Oitrusaurantium; circumttutation of epicotylwithafilamentfixed traus Terselynearits apex, tracedona liorizontal glass,from 12.13p.m.on

Feb.20th to 8.55A.M on 22nd The movement ofthe bead of the

filament wasat firstmagnified 21 times, orW\,in figureheregiven,

fromabove.

^sculus hippocastanum (Hippocastaneae).—Germinatingseeds

touch the upper end ofthe glass-plates, and, as they grew

down-with unequal

Chap I. VICIA 29

Fig 18.

it almost certain that the radiclesof

Phaseolus muUiflorus (Leguminosse)

ar-ranged in the same manner as

V ii • J rm- iii\ mi, • lines oftracks left on m

gi.nss-pl.ites by tip.

-of radicles. luAthe plate

was inclined at 70° withthehorizon,and theradicle

was1 •9 inchin length,and

23inch indiameterat base.

InBtheplatewasinclined

the radicle was a trifle

larger.

Fig 19.

sometimesrisingup andleavingthem

extremeright andleft positions

eye-piece micrometer

beanswere allowedto germinate

protruded its.radicle toalength

temunal beadwas tracedfrom8.30 a.m.to 10.30 p.m.,asshown

i.

Phaseolusmultiflorus : tracks left

oninclinedsmokedglass-plates

bytipsofradiclei; in growing

inclined at 60°,B inclined at

68° withthe horizon.

30 CIECUMNUTATION OF SEEDLINGS.

Fig 20.

Viciafaba: circumnutation ofa radicle, at first pointiiig rerti/allywards,keptin darkness, tracedon ahorizontal glass,during14hour.'.

one-half oforiginal scale.

morning,thebeadmovedtoa great distance in a nearly straight

line,in the direction indicatedbythebrokenlinein thefigure

had nowbecome muchdeclined,and hadthusgainedapositiou

Fig 21.

0. D £.fSeh faba: tracksleftoninclinedsmokedglass-plates,bytipsofradicles

at 71°, plate B at 75°,and plate E at a few degrees beneath the

Wenextexperimentedonnearlyascore of radiclesbyallowing

onlyalittlefrom the directionwhichtheyhad followed whilst

germinatingin sawdust,and theypressed lightlyonthe

a beanlaid onitsside,aflattened solid lump projected•!ofan

themselves laterallyupwards,owing to apogeotropism,atsuch

the protuberance before any arch was visible, but the basal

days extended in the same generaldirection,andwasin parts

evidence of circumnutation

Asthearchedepicotyl,inwhateverpositionitmaybeplaced,

bends quicklyupwardsthrough apogeotropism,andasthetwo

legs tend at a veryearlyage to separate from one another, as

ofTropseolum and the hypocotyl of the Cabbage The

32 CIECUMNUTATION OF SEEDLINGS.

some-what more advancedage,a filamentwas fixednearthe base of

Fig 22.

50liours ona liorizontal glass. Movement ofbeadof filament

mag-nified20times, lierereducedtoone-halfof original scale.

4 inch above the upper surface ofthe bean, instead ofclose

toit. If the beanhad been properly planted,this partof the

Lateinthe evening of the 28th,somehoursafterthe above