Papers on pollination

Charles Robert Darwin

Papers on Pollination

1861-69

MISSOURI BOTANICAL
Rannan Laras

5.

Contents

Om Orchideernes Befrugtning ved Insekter. [Tidsskr.
Naturvidensk],

Dimo®phic Condition in Primula, [Journ. Linn. Soc.
Bot., 1861].

Existence of Two Forms in Secies of Linum, [Journ.
Linn. Soc. Bot., 7, 1863].

Fertilization of Lythrum Salicaria. [Journ. Linn.
Soc. Bot., 8, 1864].

Notes on Fertilization of Orchids, [Annals and
Magazine of Natural History, 1869].

Om Orchideernes Befrugtning ved Insekter.

Af Charles Darwin — i Udtog ved M. T. Lange.

Darwins Lære om Arternes Oprindelse *) vil, hvor interes-
sant og paa mange Punkter sandsynlig den end er, dog
neppe i det hele kunne vinde Bifald. Men hvad enten man
antager den, eller forkaster den, eller indrømmer dens
Berettigelse i mange Tilfelde uden at tillegge den al-
mindelig Gyldighed — hvad der maaskee turde komme
Sandheden nermest —; eet vil ingen kunne negte: at den
Grundighed, hvormed denne udmerkede Videnskabsmand
undersoger Naturen for at begrunde sin Theori, er af
overordenlig Nytte for Naturvidenskaben og kaster nyt
Lys paa mange hidtil lidet ændsede Punkter af Naturens
Rige. Dette er saaledes Tilfældet med Orchideernes Be-
frugtning og Insekternes Medvirken derved, der vel ikke
tidligere var ganske ukjendt, idet allerede Sprengel 1793
og senere flere- andre Naturforskere have paaviist meget
derhen hørende, men som dog egenlig først har fundet
en Fremstiller og Forklarer i Darwin, der med dette For-
hold støtter sin Sætning, at alle Naturens Væsener stun-
dom behøve en Krydsning af forskjellige Individer, eller
at ingen stadig Selvbefrugtning af tvekjønnede Individer

finder Sted i Naturen. Darwins Værk (On the various-

*) See dette Tidsskr. 2. Række, 5. Bind.

Tredie Række. li. 19

Mo. Bot. Garden,
1893

274

contrivances by which British and foreign Orchids are
fertilised by insects, and on the good effects of intercrossing.
London. 1862) indeholder en Mængde omhyggelige og grun-
dige lagttagelser, der ere af stor Interesse for Botanikere;
men hans Fremstilling af Naturens vidunderlige Sammen-
pasning af disse Forhold, der hvert Øieblik overraske
baade ved Skjønhed og Snildhed, maa nødvendig kunne
interessere alle, og det saameget mere som det selv uden
botaniske Forkundskaber vil være temmelig let i Naturen
at følge og selv at see meget af det, som han fremstiller.
Her kan kun gives en Beskrivelse af Forholdet hos en-
kelte Arter, men dette skal fremstilles saa udførligt, at
enhver, der ikke vil spare den Uleilighed at sætte sig ind
i den forudskikkede Forklaring af Blomstens Bygning, vil
kunne forstaae de meddelte Omstændigheder ved Befrugt-
ningen og let selv eftersee dem i Naturen.

Blomsterdækket hos Orchideerne (Gjøgeblomsterne)
bestaaer af 3 Bægerblade, der som oftest ere farvede, og
af 3 ligeledes farvede Kronblade, af hvilke 1 i Regelen
vender nedad, er større end de andre og af meget eien-
dommelig Form. Det er »Læben«, »Honninglæben«, som
afsondrer Honningsaften, der lokker Insekterne til, og ofte
bagtil forlænger sig i en længere eller kortere Spore (Hon-
ninggjemmet).

Indenfor dette Blomsterdække findes hos vore Arter
kun 1 Støvdrager, og denne er sammenvoxet med Griffe-
len til en »Griffelstøtte«, saa at der sjeldent er mere
at see af den end Støvknappen, hvori det befrugtende
Sædstøv er indesluttet. Støvknappen er deelt i 2 Rum, der
hos de fleste af vore Arter ere meget kjendelige og saa

275

langt fjernede fra hinanden, at de see ud som 2 sær-
skilte Støvdragere. Medens Sædstøvet hos de fleste
andre Planter bestaaer af fine, løst liggende Korn, bænge
hos Orchideerne alle de smaa Korn i hvert Rum sammen
og danne Smaaklumper eller Masser, der ofte bæres af
en meget eiendommelig Stilk. Disse Smaaklumper til-
sammen med Stilken kaldes Støvmassen.

Der skulde egenlig være 3 Grifler, men de ere heelt
voxede sammen med Undtagelse af Arrene, og af disse
flyde selv de to nederste ofte saa fuldstændigt sammen, at
de see ud som eet; — kun disse to have Arrets sædvan-
lige Egenskaber og Bestemmelse, nemlig under Befrugt-
ningen at gjennemtrænges af Støvkornenes lange, fine
Rør, der føre Indholdet ned til Æggene i Frøgjemmet;
— det tredie Ar derimod, der sidder øverst, er omdannet
til et usædvanligt Redskab, som kaldes Snabelen og hos
mange Orchideer slet ingen Lighed har med et virkeligt
Ar. Den indeholder eller bestaaer af et klæbrigt Stof, og
hos mange Orchideer ere Støvmasserne fasthæftede til en
Deel af dens Yderhud, der bliver hængende ved dem,
naar de bortføres af Insekter. Den Deel, som saaledes
kan borttages, bestaaer hos de fleste af vore Arter af et
lille Stykke Hud, som Darwin kalder Klæbeskiven, med et
Lag eller en Klump klæbrig Materie under; men hos
mange udenlandske Arter er Klæbeskiven saa stor, at
dette Navn kun passer paa en Deel af den, medens den
anden, paa hvis Top Støvmasserne sidde, kaldes Snabe-
lens Fod eller Stilk.

De indenlandske Orchideer inddeler Darwin nu i 3
Grupper, af hvilke den første indbefatter de fleste af
vore almindelige Arter, navnlig Slægten Orchis (Gjøgeurt).
Støvmasserne hos denne Afdeling have forneden en med

19 *

276

Klæbeskiven sammenvoxet Stilk og Støvknappen er for-
bunden med Snabelen.

Fig. 1. Orchis mascula.

A. En Blomst seet fra Siden, Bæger- og Kronblade ere borttagne med Unåtagelse
af det halve af Læben og det meste af Sporen. B. Blomsten seet forfra, Alle Blade
borttagne undtagen Læben. C. En Støvmasse med de smaa Pakker af Støvkorn, Stilken
og Klæbeskiven. D. Snabelen seet forfra med nedtrykt Læbe. E. Gjennemsnit af
Snabelen med den deraf indesluttede Klæbeskive og Stovmassens Stilk. F. Smaa-
pakker af Støvkorn, sammenlænkede ved elastiske Traade, der i Fig. ere trukne ud
fra hverandre.

a. Støvknappen. c. Støvmassens Stilk. d. Klæbeskiven. l. Leben. n. Hon-
ningsporen. p. Støvmassen. r. Snabelen. s. Arret.

api:

277

+

Orchis mascula (tyndaxet Gjogeurt) forekommer
hyppigt hos os om Foraaret i Krat. I Fig. 1 ere Beger-
og Kronblade borfskaarne med Undtagelse af Leben med
Honninggjemmet, der sees i A, n. De to Ar ere næsten
sammensmeltede til eet (s), der sees under den pungfor-
mede Snabel (r). Stevknappen (A, a og B, a) vise to langt ad-
skilte Rum, der fortil ere aabnede paalangs og hver inde-
holde en Stovmasse. C viser en saadan Stovmasse ud-
taget af sit Rum. Den bestaaer af et Antal Smaapakker
af Stevkorn, der ere indbyrdes forbundne ved fine og
meget elastiske Traade, I F fremstilles disse trukne ud
fra hverandre. Disse Traade smelte sammen ved den
nederste Ende af hver Støvmasse til en lige elastisk Stilk
(C, c). Enden af Stilken hænger fast sammen med Klæbe-
skiven (C, d), der i E sees i Gjennemsnit paalangs, og be-
staaer af et lille ovalt Stykke Hud og en Klump klæbrig
Materie ved dets Underside. Enhver Støvmasse har sin
særegne Klæbeskive, og de to Klumper klæbrigt Stof ligge
begge indesluttede i Snabelen (D).

Denne (A,r og B,r) er næsten kuglerund, noget tilspidset
og hænger ud over de to Ar. Den behøver en fuldstæn-
dig Beskrivelse, da enhver Enkelthed i dens Bygning er
vigtig. E fremstiller et Gjennemsnit paalangs gjennem
en af Klæbeskiverne og Klumperne, og D begge seete for-
fra i Snabelen, hvis forreste Læbe er trykket noget ned:
Den nederste Deel af Støvknappen er forenet med Ryg-
gen af Snabelen (B). Paa et tidligere Udviklingstrin be-
staaer Snabelen af en Masse mangekantede Celler fyldte
med bruun Materie, som snart opløse sig til to Klumper
halvflydende, meget klæbrig og strukturløs Substans. Disse
halvflydende Klumper ere noget langagtige, foroven oftest
flade, forneden hvælvede. De ligge næsten frit i Snabe-

278

è

len, omgivne af Vædske og blot paa Bagsiden sammen-
hængende med en lille Skive af Snabelens Yderhinde,
den ovenfor beskrevne Klæbeskive, der bærer Støvmas-
sens Stilk.

Den Hud, som danner den hele ydre Overflade af
Snabelen, er i Begyndelsen sammenhængende; men saa-
snart Blomsten aabner sig, bevirker selv den sagteste Be-
rørelse, at den brister i en buet Tværlinie paa Forsiden,
hvorved Snabelens Form ikke forandres, men dens for-
reste Deel bliver derved en Læbe, som let kan trækkes
ned, (I B sees Randen opret, i D nedtrykt). Trykkes
Læben heelt ned, saa komme de to Klumper klæbrig Ma-
terie til at ligge frit; men saasnart Trykket ophører,
springer Læben op igjen paa Grund af den bagerste Deels
Elasticitet og indeslutter paany de to Klumper.

Den mindste Berørelse og endogsaa Chloroformdampe
bevirke denne Bristen af Huden i en bestemt Linie; maa-
skee brister den ogsaa undertiden af sig selv, ialtfald for-
beredes det ved en Svækkelse langsmed den betegnede
Linie. Samtidig med at Huden brister foran, synes den
ogsaa at briste bagtil i to ovale Linier, hvorved de to smaa
Klæbeskiver adskilles fra Snabelens øvrige Yderflade. Da
Støvknappens to Rum allerede for Blomstens Udspringning
have aabnet sig fortil fra Grunden til Spidsen, saa ligge
begge Støvmasserne nu, naar Snabelens Læbe trykkes
ned, fuldkommen frit, men endnu paa deres Plads; nem-
lig Støvmasserne selv og deres Stilke i Støvknappens Rum
og de smaa, klæbrige Klumper, som ved Klæbeskiverne
ere forbundne med dem, i Snabelens Pung.

Vi skulle nu see, hvorledes denne sammensatte Me-
kanisme virker. Lad os antage, at et Insekt sætter sig
paa Leben af Blomsten, der frembyder en god Landings-

279

plads, og stikker sit Hoved ind i Kammeret, paa hvis
bagerste Væg Arret (A, s og B, s) findes, for at naae ned i
Honningsporen med sin Sugesnabel — eller, hvad der
gjor samme Virkning, lad os skyde den fine Spids af en
Blyant meget forsigtigt ind i dette Honninggjemme. Da
den pungdannede Snabel rager frem i den Vei, som forer
til Honninggjemmet, er det neppe muligt at fore nogen
Gjenstand ind i dette uden at berøre Snabelen. Dens
Yderhud vil derved briste langs med den førnævnte Linie
og Læben eller Pungen let kunne trykkes ned. Naar dette
er skeet, maa.en:- af de
klæbrige Ulumper, eller
begge, nødvendigviis kom-
me i Berøring med det
indførte Legeme og ved
sin store Klæbrighed blive
hængende derved. Men

da denne Materie frem-

deles har den Særegen-

Fig. 2.

hed, at den -i faa Minuter A Seiten te nee ae eee
tørrer ind og stivner som hæftet sig paa Blyanten, B. Samme efter at
den har boiet sig ned.

Kit. og da Stovknappens
Rum i Forveien ere aabne fortil, saa vil en af Stevmas-
serne, eller begge, klebes fast til Insektets Hoved eller
Blyanten og trekkes ud med, omtrent som det fremstilles
i. Fig. 2::A¢

Det er ganske nødvendigt, at Stovmasserne klæbe sig
saa fast; thi hvis de faldt ud til Siden eller tilbage, vilde
de slet ikke kunne befrugte Blomsten. Efter den Stilling,
hvori begge Stovmasserne sidde i deres Celle, beholde de
ogsaa en lidt divergerende Retning påa det fremmede
Legeme, som de nu ere hæftede til. Vedbleve de nu at

280

beholde denne oprette, divergerende Stilling (Fig. 2 A),
vilde de igjen komme tilbage paa deres gamle Plads, hvis
vi igjen førte Blyanten ind i samme eller en anden Blomsts
Honninggjemme, og ingen Befrugtning finde Sted. Hvor-
ledes bevirkes da Blomstens Befrugtning? Det skeer ved
en smuk Indretning; medens nemlig den klæbrige Over-
flade holder fast, er den uanseelige lille Hudskive, hvor-
paa Stilken sidder, udrustet med en mærkværdig Sammen-
trekningskraft, hvorved Støvmassen nodes til i Løbet af
omtrent 30 Sekunder at bøje sig ned imod Blyantens
eller Sugesnabelens Spids i en Bue af 90°, indtil den
faaer den i Fig. 2 B angivne Stilling. Imidlertid flyver
Insektet til en anden Blomst, hvor da, som Fig. 1 viser,
den tykke Ende af Støvmassen netop maa træffe Over-
fladen af Arret, naar Sugesnabelen eller Blyanten føres
ind i Honninggjemmet.

Her kommer nu en anden interessant Indretning,
som R. Brown for lang Tid siden har beskreven, i Betragt-
ning. Arret er meget klæbrigt, men ikke nok til at
sonderrive hele Stevmassen, hvormed det nu kommer i
Beroring. Det kan kun adskille de elastiske Traade, som
forbinde de smaa Pakker af Stovkorn med hverandre
(Fig. 1 F), og fastholde nogle af dem. Derfor kan den
ene Stovmasse paa Insektets Hoved komme i Berøring
med flere Ar efter hinanden og efterhaanden befrugte
dem alle, saa at Insektet kun beholder Stovmassens Stilk
tilbage.

Endnu et Par smaa Omstendigheder ere verd at
legge Mærke til. De smaa Kiumper klæbrig Materie om-
gives i Snabelen af en Vedske, hvad der er vigtigt, fordi
denne Materie, som sagt, torrer meget hurtigt ind i Luf-
ten og i Løbet af faa Minuter taber Evnen til at klæbe

281

sig fast. Dernæst sidde de smaa Hudskiver, hvis Sam-
mentrækning bevirker den Sænkning af Støvmasserne, der
er saa nødvendig for Befrugtningen, bag i og nede i
Snabelen, tæt omgivne og derved holdt fugtige af Støv-
knappens Basis — hvad der ogsaa er nødvendigt, da blot
30 Sekunders Udsættelse for den frie Luft er nok til at
bevirke Senkningen. Endelig er det meget vigtigt, at
Leben, som forhen omtalt, igjen springer tilbage i sin
forrige Stilling, naar den er bleven trykket.ned. Naar et
Insekt havde trykket den ned, men ikke medtaget nogen
eller kun den ene af de klæbrige Klumper, vilde nemlig
ellers begge Klumperne, eller den ene, som blev tilbage,
udsættes for Luften og hurtigt tørre hen, saa at Støv-
masserne nu bleve unyttige. Men nu er det vist, at af mange
Orchidee-Arter bortføre Insekterne kun een Støvmasse ad
Gangen, og det er sandsynligt, at dette er det alminde-
ligste Tilfælde, da de nederste Blomster, som længst have
været udsprungne, sædvanligviis slet ingen Støvmasser
indeholde, men de yngre, nys udsprungne, oftest
have den ene tilbage. Saaledes fandt Darwin i Axet af
en Orchis maculata ti Blomster, og det især de øvre,
hvori der kun var een Støvmasse tilbage, men den hele
Mekanisme var iøvrigt i Orden, saa at de kunde bortføres
af Insekterne.

Hvad der hidtil er sagt om Indretningen hos Orchis
mascula, passer i alt væsenligt ogsaa paa Orchis Morio,
fusca, maculata og latifolia; derimod finder der en væsen-
lig Forskjel Sted hos Orchis (Anacamptis) pyramidalis
(Horndrager — hos os meget sjelden i Skove paa Kalk-
grund) *). Denne Art, der er, afbildet i Fig. 3, har to

*) Med denne Art stemmer Orchis ustulata i det vesenlige overeens.

282

runde, heelt adskilte Ar (A, ss), el paa hver Side af den
pungformede Snabel (r). Denne sidder ikke over Hon-

Fig. 3. Orchis pyramidalis.

A. Blomsten seet forfra, Alle Blade borttagne undtagen Leben. B. Samme fra
Siden. Den halve Lebe og et Stykke af det overste af Leben bortskaarne. C.
Begge Stovmasser paa den sadelformede Klebeskive. D. Samme efter Sammen-
trekningen, naar den ikke er fastheftet til noget. E. Stovmasserne, som have hef-
tet sig til en Naal, der er fort ind i Honninggjemmet. F. Samme efter at de have
boiet sig ned. è

a Støvknappen. s.s Arret. r Snabelen. 1 Leben. 1' Læbens Ribber. n Hon-

ningsporen.

283

ningsporen, men saa dybt, at den dækker og tildeels
lukker dens Munding (smlg. B). Honninggjemmets For-
kammer, der dannes af Leben og Griffelstotten og er
rummeligt hos Orchis mascula og dens beslægtede Arter,
‘er her kun lille. Snabelen er forneden i Midten udhulet
og fyldt med en Vedske. Der er kun een Klebeskive af
Form som en Sadel (C), der paa sin næsten flade Ryg
bærer de to Stovmassers Stilke. Saalenge Snabelens Hud
ikke er bristet, er det næppe muligt at see, at den sadel-
formede Skive udgjor en Deel af Snabelens sammenhen-
gende Overflade, da den tildeels skjules og holdes fugtig
af de to Støvknaprums Grundhinder, der foldes vidt ud
over den. Skivens øvre Hud bestaaer af flere Lag smaa
Celler og er derfor tyk; forneden er den overtrukket af
et Lag meget fast klæbende Materie, som dannes i
Snabelen.

Naar Snabelens Læbe er trykket ned ved en eller
anden svag Berøring, blottes den nederste Deel af Klæbe-
skiven, som ikke forandrer sin Plads, og den kan nu
klæbe sig fast til en Gjenstand, som berører den; et Haar
er endogsaa stivt nok til trykke Læben ned, og Sadelens
klæbrige Overflade hæfter sig da til det. Endelig er
Leben forsynet med to ophoiede Ribber (A, I’ og B, 1‘), der
udenfra indad lobe skevt sammen imod Midten som en
Fiskeruse og derved ere fortræffelig skikkede til at lede
et boieligt Redskab, som en Borste eller et Haar, ind i
den lille, rundagtige og derhos tildels af Snabelen sper-

rede Munding af Honninggjemmet.

Naar nu en Sommerfugl — disse Dyr besøge meget
hyppigt Orchideerne — stikker sin Sugesnabel ind mellem

Lebens ledende Ribber, eller naar man efterligner denne
Bevægelse med en fiin Borste, saa vil den ledes sikkert

284

ind i Honninggjemmets fine Munding og vil neppe kunne
undgaae at trykke Snabelens Læbe ned. Derved kommer
Børsten i Berøring med den sadelformede Skive, som nu
er blottet og klæber sig fast og følger med tilligemed de
to Støvmasser, naar Borsten trækkes tilbage: Saasnart
Sadelen kommer ud i den frie Luft, pleier der øieblikke-
ligt at foregaae en rask Bevægelse med den, idet begge
Endelapperne krumme sig indad og omfatte Børsten.
Drages Støvmasserne derimod ud med en Tang, uden at
'Sadelen faaer noget at omfatte, saa rulle Enderne sig i
Løbet af faa Sekunder tæt sammen (D). Mange Sommer-
fugles Snabel er saa tynd, at Sadelen netop omfatter den,
saa at Enderne naae sammen under den, hvorfor en
Naturforsker, der saae en Sommerfugl med Støvmasserne
påa Snabelen, blev forledt til at troe, at den havde
boret Snabelen midt igjennem Støvholderen.

Denne raske Sammenbøining tjener til at befæste
Sadelen med dens Stovmasser oprette paa Sugesnabelen.
Dog vilde dette kunne opnaaes alene derved, at Klebe-
stoffet størkner meget hurtigt, saa at den egenlige Hen-
sigt snarere er, at Stevmasserne derved boie sig ud fra
hinanden. ‘Thi da de sidde paa Sadelens flade Ryg, saa
rage de i Begyndelsen lige op i parallel Retning, men alt
som Sadelen krummer sig om Snabelen, maa de nødven-
digviis beies ud fra hinanden. Men neppe er denne Be-
vegelse endt, hvad der medtager en halv Snees Sekun-
der, for der begynder en anden Bevegelse, der ligesom
den forste alene bevirkes af den lille Hudskives Sammen-
trekning, og nu er ganske den samme, som for blev be-
skreven ved Orchis mascula, idet Stovmasserne fra den
lodrette Stilling boie sig i en ret Vinkel ned mod Sna-
belens Spidse, saa at de ligge parallelt med den (E. F).

285

Hensigten med denne dobbelte Bevægelse bliver klar,
naar man fører Børsten med Støvmasserne tiibage, efterat
Bevægelsen er endt (smlg. A og F). Thi nu have begge
Støvmassernes Ender netop faaet en saadan Stilling, at
den ene strøifer Arret paa den ene Side, den anden
paa den anden Side, saa at de klæbrige Ar nu kunne
løsne de elastiske Traade og fastholde nogle af Støv-
kørnene,

Da der ikke hos andre Planter, neppe hos noget Dyr,
findes fuldkomnere Tilpasning af Organerne, end hos disse
Orchideer, saa fortjener det ovenfor beskrevne vel endnu en-
gang at sammenfattes i Korthed. Blomsternes glimrende
Farver tiltrække Dagsommerfuglene, deres eiendommelige
Lugt Natsommerfuglene. Det øvre Bægerblad og de to øvre
Kronblade danne en Hætte til Beskyttelse for Støvknap-
pene og Arrene. Læben er udviklet til et langt Honning-
gjemme, hvis Indhold drager Sommerfuglene til og er

saaledes opbevaret, — ganske anderledes end i andre
Familier — at det kun langsomt kan opsuges for at give

det klæbrige Stof under Sadelen Tid til at størkne. De
sammenløbende Ribber paa Læben lede Sugesnabelen i
den rigtige Retning, for at Støvmasserne ikke skulle komme
til at sidde skjævt og gaae forbi Arrene.. Snabelen er
opstillet paa Veien til Honningsaften som en Snare paa
Vildtets Vei; den er saaledes bygget, og de Linier, hvor-
efter den brister, saaledes dragne, at Sadelen dannes for-
oven, Pungens Læbe forneden. Denne Læbe er saa let
at trykke ned, at Klæbeskiven ikke godt kan undgaae at
blottes og hæfte fast ved Insektets Sugesnabel, og skulde
det ikke skee, saa springer den elastiske Læbe igjen op,
bedækker paany den klæbrige Flade og holder den fugtig
til næste Gang. Vi see fremdeles, at det klæbrige Stof i

286

Snabelen er befæstet alene til Klæbeskiven og omgivet af
Vædske, saa at det ikke kan størkne, før Skiven drages
ud, ligesom Sadelens Overflade holdes fugtig indtil Ud-
dragningen, da den eiendommelige Boining af Stovmas-
serne begynder, forst til Siden og saa fremad, en Boining,
der er noiagtigt beregnet paa at bringe begge Stevmasser-
nes Ender i Berøring med Arfladerne. Disse Flader ere
klebrige nok til at fastholde nogle Stovpakker, medens
de overlade Resten til andre Blomster. — Endvidere maa
mærkes, at selv om Insektet bruger lang Tid til at op-
suge Honningsaften, saa begynder Stovmassernes Boining
ikke, for de ere trukne fuldstændigt ud af deres Rum, og
at deres Bevegelse forst et halvt Minut efter er saa vidt
fuldendt, at de kunne treffe Arrene, naar de paany fores
ind i en Blomst, saa at Insektet faaer Tid nok til at
flyve til en ny Plante og saaledes befrugte den med en
andens Støv.

De hidtil omtalte Orchis-Arter behøve nødvendigviis
Insekters Medvirkning til deres Befrugtning. Dette frem-
gaaer af, at Støvmasserne ligge saa fast i deres Rum og
Klæbeskiverne i Snabelen, at de ikke kunne rystes ud;
men Darwin har yderligere godtgjort det ved Forsøg, idet
han bedækkede adskillige Planter med Glasklokker, saa at
Adgangen spærredes for Insekterne, hvorved det viste sig,
at ingen Bestøvning fandt Sted og ingen Frø ansattes,
skjøndt Planterne iøvrigt intet led.

Det synes efter Darwins Iagttagelser især at være
Sommerfugle, der bestøve Orchis-Arterne; han nævner 23
Årter, paa hvis Snabel han har fundet Støvmasser af
Orchis pyramidalis. Dog deeltage ogsaa mindre Insekter,
f. Ex. Empis-Arter, i Bestøvningen og bortføre Støvmasserne
paa Hovedet eller Brystet. Hvorvidt derimod Darwins

287

Mening, — at nogle sjeldne Arter, f. Ex. Orchis fusca, skulde
vedblive at være saa sjeldne, fordi de ikke tiltrække In-
sekter nok, eller fordi de kun besøges af enkelte Arter,
— er rigtig, turde være tvivlsomt, da Grunden ligesaa
vel kan søges i andre Forhold, og Jordbunden aabenbart
har megen Indflydelse herpaa.

Men endnu staaer der tilbage at omtale en mærkelig
Omstændighed ved de omtalte Orchis-Arter, nemlig at deres
»Honninggjemme«, som skulde lokke Insekterne til, ingen
Honningsaft indeholder! Sprengel har undersøgt de
fleste Arter, flere andre efter ham, og Darwin har anstillet
mangfoldige Undersøgelser til de forskjelligste Tider, selv
om Natten, i Solskin og i Regnveir, men selv ved Hjælp
af Mikroskopet har han aldrig fundet mindste Spor af
Saft i Honningsporen. Hvorledes skal man forklare sig
dette? — Sprengel kaldte disse Blomster »Scheinsaft-
blumen«; han antog, at her fandt et systematisk Bedrageri
Sted, at insekterne, uagtet de bestandig skuffedes, dog
bestandig kom igjen for at søge Honningsaft; men vi maa
give Darwin Ret i, at det er umuligt at troe paa et saa
kæmpemæssigt Bedrageri, naar man erindrer, hvor uhyre
ofte det maatte gjentages. Og naar man husker, at Be-
støvningen forudsætter, at Insektet gjentager sit Besøg hos
disse Blomster flere Gange umiddelbart efter hinanden,
saa maatte man, for at give Sprengel Ret, sætte Insek-
ternes Forstand eller Instinkt meget lavt og kunde dog
ikke forklare Grunden til, at disse Blomster vare saa
overordenligt snildt indrettede, men at et af de vigtigste
Led i Kjæden manglede. Imod Rigtigheden af Sprengels
Mening taler ogsaa i hei Grad hvad Darwin har iagttaget,
at monstrøse Blomster, som manglede Honninggjemmet,
men hvis Befrugtningsapparat var i fuldstændig Orden,

288

ikke vare blevne berøvede deres Støvmasser, medens dette
var Tilfældet med alle de fuldstændige Blomster i samme
Ax. Et Forsøg, som Darwin anstillede ved at skjære
Euden af Honninggjemmerne paa endeel Blomsterknopper
hos Orchis pyramidalis, førte til et lignende Resultat, saa
at Insekterne ikke synes at lade sig saa let narre.

Men hvor er da Nøglen til denne Gaade? Darwin
synes at have fundet den, idet han bemærkede, at den
indre og ydre Væg i Sporen hos disse Orchideer skilles
ved et temmelig vidt Mellemrum, at dette er opfyldt af
Vædske, og at den indre Væg eller Hinde er meget fiin
og særdeles let gjennemtrænges af Vædsken; medens der
ikke findes noget saadant Mellemrum hos Gymnadenia
conopsea og Platanthera solstitialis *), hvis Sporer altid
ere fyldte med fri Honningsaft. Han sluttede deraf, at
Insekterne med deres Sugesnabel kunne gjennembore den
fine Indrehud i hine Arters Honningsporer og opsuge
Vædsken fra Mellemrummet. Naar man seer, hvor mange
sindrige Foranstaltninger der ere trufne for Orchideernes
Befrugtning, og af hvor stor Vigtighed det er, at Støv-
masserne komme til at sidde fast paa insektet og ikke
falde til Siden eller tilbage, og naar man erindrer, at
Klæbeskiven behøver nogen Tid for at sætte sig fast ved
Saftens Størkning, saa at det vilde være til stor Nytte om

Insektet blev lidt opholdt i at indsuge Saften, saa synes
"det ikke urimeligt at antage, at den usædvanlige Indret-
ning, at Honningsaften afsondres indenfor Overhuden, er

truffen her for at node Insekterne til et længere Ophold,

*) Darwin nævner ikke, om det samme er Tilfældet med de andre
Arter, hvis Sporer indeholde fri Honningsaft.

289

medens de paa flere Steder gjennembore denne Hinde og
udsuge Saften af Mellemrummene.

Rigtigheden heraf bestyrkes ved en Undersøgelse af
Klæbeskiven hos de Arter, hvis Sporer indeholde fri Hon-
ningsaft, nemlig Gymnadenia conopsea og albida, Platan-
thera solstitialis og chlorantha og Coeloglossum viride.
Hos de fire første er Klebeskiven ikke indesluttet i en Pung,
men nøgen, hvoraf man strax seer, at den klæbrige Ma-
terie maa have en anden kemisk Beskaffenhed end Orchis-
arternes og ikke saa hurtigt størkne, hvilket Darwin og-
saa har overbeviist sig om ved Forsøg, der viste, at
Skiven beholdt sin Evne til at klæbe sig fast i flere (2—24)
Timer. Hos den sidste Art er Klæbeskiven vel bedækket
af en pungformet Hinde, men denne er saa lille, at
Botanikerne have overseet den, og Skiven bevarer ogsaa,
ligesom de andre Arters, sin Klæbrighed i længere Tid
efter Udtagelsen. Da den klæbrige Materie hos disse fem
Arter altsaa formaaer at hæfte Støvmasserne tilstrækkelig
fast paa insekterne uden strax at størkne heelt”), saa
vilde det ikke nytte, at Insekterne opholdtes længere med
at suge Saften op, og derfor finde vi hos dem og hos dem
alene Saften frit i Honninggjemmet. Hvis dette Sammen-
stød — paa den ene Side af et langsomt størknende
Klæbestof og en Opbevaring af Honningsaften, der op-
holder Insekterne i længere Tid, paa den anden Side af et
Klæbestof, der fra først af er meget seigt, og en Opbe-
varing af Saften, der tillader en hurtig Indsugning — er
tilfældigt, saa er det et meget heldigt Tilfælde for disse

*) Det egenlig bevisende: at Klæbestoffet hos disse Arter strax er
tilstrækkelig seigt til at lade Stovmasserne sidde saa fast som
fornedent, har Darwin dog ikke paaviist. Den lange Tid der med-
gaaer til fuld Sterkning synes derfor at tale for det modsatte.

Tredie Række. li. 20

290

- Planter, Men er det ikke tilfældigt, saa er det et heist
mærkeligt Exempel paa Tilpasning.

De ovrige indenlandske Arter af denne Gruppe
(Slægterne: Gymnadenia, Platanthera, Coeloglossum, Her-
minium og Ophrys) skille sig fra de hidtil omtalte ved
to adskilte Snabler. Neppe to Arter stemme iøvrigt over-
eens i Blomstens Indretning til Befrugtningen, men da
Afvigelserne fra det i det foregaaende beskrevne ikke ere
meget store, skal jeg indskrænke mig til at omtale et Par
mærkeligere Tilfælde.

Hos Slægterne Ophrys og Herminiura mangler Hon-
ningsporen, men erstattes, af en Fordybning i Læbens
nedre Deel, der dog, ligesom Orchisarternes Spore, ingen
fri Honningsaft indeholder. At Klæbeskiven hos nogle
Arter er nøgen og den klæbrige Materie derfor af en an-
den Beskaffenhed, er allerede omtalt. At Pungen, som
indeslutter Klæbeskiven hos de fleste andre Arter, ikke er
elastisk som hos Orchisarterne, hvor den igjen springer til-
bage i sin Stilling, naar en Støymasse er udtagen, — en
Elasticitet, som her vilde, være unyttig, da hver Snabel
kun indeslutter 1 Klæbeskive, — er et Vidnesbyrd om
Midlernes Tilpasning til det Maal, der skal naaes.

Hos Ophrys myodes og Coeloglossum viride
(to Arter, der ere meget sjeldne her i Landet) findes der
vel ogsaa en Pung, men den nederste Deel af Støvmas-
sernes Stilk og Klæbeskivens øvre Deel ere ikke indeslut-
tede deri, og da de saaledes ere udsatte for Luftens Paa-
virkning, mangle de den eiendommelige Evne til at bøie
Støvmassen ned i Retning af Arret. Hos Ophrys myodes
erstattes denne Mangel derved, at Stilken i sit naturlige
Leie har en dobbelt Boining næsten under en ret Vinkel;
dog synes denne Indretning ikke tilstrækkelig til sit For-

294

maal, der kun kan opnaaes ved en gjentagen Hæven og
Sænken af Insektets Hoved, Det staaer da efter al Sand-
synlighed i Forbindelse hermed, at Støvmasserne hos
denne Art efter Darwins lagttagelser meget sjeldnere
bortføres end hos de andre Orchideer, og at den kun
meget sjeldent og sparsomt udvikler sine Frokapsler.
Indretningen hos Coeloglossum viride er meget afvigende
og fortjener en nærmere Beskrivelse. Arret er her lille
og stillet i Midten af Blomsten, medens Stovmasserne
ligge høit over det, og de 2 Punge, der indeslutte Klebe-
skivernes nedre Deel, ere fjernede langt fra hinanden ud
til Siden af Biomsten, saa at et Insekt, der opsugede
Honningsaften af Sporen, hvis Aabning findes lidt foran
og under Arret, ikke vilde komme i Berøring med Klebe-
skiverne, selv om det løftede Hovedet i Veiret. "Men der
er sorget for, at dette alligevel skeer, paa den merkelige
Maade, at der paa hver Side af Lebens Grund, lige under
Klaebeskiverne, findes en lille Fordybning omgivet af
Lebens ophoiede Rande, hvori der afsondres Honning-
draaber. Tilmed er der en lang opheiet Ribbe lige under
det rigtige Honninggjemme, der leder Insekterne til at
sætte sig paa Siden af Leben tet ved det mindre Hon-
ninggjemme, Opsuge de nu først Saften af dette, ville
de næppe kunne undgaae at bortføre Stevmassen, og naar
de derefter vende sig til det egenlige Honninggjemme,
vil den netop komme til at berøre Arret. Skjondt det
saaledes i Regelen vil vere med Blomstens eget Stov, at
Arret befrugtes, er en Krydsning mellem forskjellige
Blomster dog ikke udelukket; i det Tilfælde nemlig at
Insektet først opsugede Hovedbeholdningen og derefter
Randdraaberne, vilde det flyve til den neste Blomst med

20*

292

Stovmasserne paa Hovedet og kunde saaledes bestøve
dennes År.

Før vi forlade denne Gruppe, maa vi endnu opholde
os nogle Øieblikke ved Ophrys apifera, en i England
og Sydeuropa, men ikke i Danmark, forekommende Årt,
fordi den, saavidt vides, er det eneste Exempel paa nor-
mal Selvbefrugtning af en Orchidee”. Dens to pung-
formede Snabler, Klæbeskiverne og Arrenes Stilling ere
omtrent som hos de andre Ophrysarter, men Støvmas-
sernes Stilke ere meget lange, tynde og boielige, saa at
de mangle den fornødne Stivhed til at holde sig oprette,
som de ellers have hos alle Arter i Gruppen. Da Støv-
knappens to Rum ere bøiede stærkt fremad, have Stilkene
foroven den samme Retning, og de pæreformede Støv-
masser sidde derfor lige over Arrene. Strax efter Blom-

stens Aabning aabne ogsaa Støvknappens Rum sig, — og
det usædvanlig vidt — og Støvmasserne falde ud. Da

Stilkene ere saa svage, begynde de meget snart efter at
synke nedad, saa at Støvmasserne hænge frit i Luften
lige foran og i Højde med Arrene, medens Klæbeskiverne
vedblive at holde deres nedre Ende fast i Pungen. En
svag Luftstrømning er nu tilstrækkelig til at lade dem be-
røre Arret, ved hvilket de klæbe fast, hvad Darwin har
overbeviist sig om ved Forsøg, idet han omgav” Blom-
sterne med et Net, der holdt Insekter, men ikke Luft-
strømme borte. Udelukkedes derimod Luftstrømningen,
vedbleve Støvmasserne ogsaa at svæve i Luften foran
Arret. Bestøvningen gaaer paa denne Maade saa regel-

mæssigt for sig i Naturen, at Støvmasserne næsten altid

*) En meget mangelfuld Selvbefrugtning forekommer hos Cephalan-
thera grandiflora, som siden skal omtales.

293

findes paa deres Ar og Frøkapslerne næsten aldrig slaae
feil — medens det omvendte er Tilfældet hos Ophrys
myodes. — Det er unægtelig" hoist mærkeligt, at denne
Indretning til Selvbefrugtning ikke findes hos de andre
Ophrysarter, ikke engang hos Ophrys arachnités, der dog af
flere Botanikere ansees for at være kun en Varietet af
Ophrys apifera; og man fatter let, at Darwin af denne
Omstendighed i Forbindelse med, at Ophrys apifera des-
uagtet har alle de nodvendige Indretninger til at befrugtes
som de andre Arter, ledes til den Formodning, at der
hos denne Art har skullet bevirkes en rigeligere Udvik-
ling af Fre — hvad der kun kunde skee med Opgivelse
af de Fordele, som Krydsningen kunde medfore; men at
en saadan Krydsning med andre Individer dog i enkelte
Tilfælde finder Sted, om end sjeldent. Dog, ‘disse Gis-
ninger kunne vi her lade staae hen.

Vi komme nu til en anden Hovedafdeling af Orchi-
deerne, som have en fri, bag Arret stillet Stovknap.
Stevkornene ere sammenlenkede ved fine, elastiske Traade,
der tildeels hænge sammen og rage frem ved den øverste
Ende af Stovmasserne og ere befæstede til Ryggen af
Snabelen, hvorfor de mangle Stilken, der spiller en saa
vigtig Rolle hos de forhen omtalte. Af de herhen hørende
Slegter: Epipactis, Cephalanthera, Goodyera og Spiranthes
skulle et Par Arter her nærmere omtales.

Hos Epipactis palustris (Sump-Huullebe), der fore-
kommer hist og her i vaade Enge, rager den forreste
Deel af Arrene noget frem foran Griffelstviten (Fig. 4,
B,s og C,s). Paa dens Top sidder en enkelt lille, nesten
kugleformet Snabel (B, r og C, ri, hvis Forside rager noget
frem foran Overfladen af Arrene, hvad der er af megen
Vigtighed. I ung Tilstand bestaaer Snabelen af en skjør

294

Cellemasse med ru Yderflade; disse Yderceller forvandles
under Udviklingen til en blød, glat og meget elastisk Hud,
der er saa overordenlig fiin, at et Haar kan trænge igjen-

Fig. 4. Epipactis palustris.

A. Blomsten seet fra Siden; kun de nederste Begerblade borttagne. B. Samme
med alle Blade borttagne undtagen Halvdelen af Leben. C. Griffelstotten seet for-
fra. Snabelen er i Afbildningen noget nedtrykt; den rager i Virkeligheden noget
hoiere op og skjuler mere af Stevknappens Rum.

a. Stevknappen, hvis to aabne Rum i C sees forfra. a‘. Rudimenter Stovknap.

1, Leben. r. Snabelen. s. Arret.

nem den. Ved den svageste Gnidning, stundom maaskee
ogsaa uden en saadan, bliver denne Overflade klæbrig,
saa at Støvkornene blive hængende ved den. Denne bløde
Yderhud danner en Kappe om Snabelen og er forinden
overtrukken af et mere klæbrigt Lag, som i Luften størk-

aia ai

295

ner i Løbet af 5—10 Minuter, Denne hele Kappe med
dens indvendige Beklædning bortføres særdeles let, naar
et Legeme skydes let imod den, i Retningen opad og til-
bage, og der bliver da kun en lille Stump tilovers ved
Grunden. I Knoppen rager Støvknappen ganske frit op
bag Snabel og Ar; den aabner sig paalangs før Blomsten
springer ud, saa at de to ovale Støvmasser ligge frit og
løst i deres Rum. De bestaae af runde Smaakorn, der
hænge sammen 4 og 4, og disse ere forbundne ved frie,
elastiske Traade, der i Knipper strække sig langs Midter-
linien af hver Støvmasses Forside, hvor de komme i Be-
røring med den øvre Deel af Snabelens Ryg, der før
Blomstens Aabning er lænet mod Støvknappen, og fæste
sig til dens Kappe. Derefter krummer Snabelen sig
fremad og trækker dérved Støvmassserne tildeels frem af
deres Rum. Støvknappens øverste Ende bestaaer af en
stump, solid Spids uden Støv, der rager noget frem over
og foran Snabelen (B, a og C, ai. Blomsterne staae næsten
lodret ud fra Stængelen (A). Leben bestaaer af to Dele:
den nederste danner en Skaal, der indeholder Honning-
saft; den øverste, der kun hænger sammen med den
nederste ved et smalt, boieligt og meget elastisk Led, er
krummet opad, saa at den tildeels lukker for Blomsten.
En Flues Vægt er tilstrækkelig til at bøje den ned i den
i B fremstillede Retning, men naar Vægten borttages,
springer den igjen op i sin forrige Stilling.

Lad os nu see, hvortil alt dette tjener. At trykke
Snabelen ned, som hos de forhen beskrevne Arter, løsner
ikke Støvmasserne, Et Insekt, der satte sig paa Læbens
øvre Deel for åt suge Saften op, vilde slet ikke komme
til at berøre Snabelen; naar det derimod var krøbet ind i
Blomsten, og Læben altsaa havde lukket i for det ved at

296

rette sig op, vilde det være nødt til at kravle op ad Arret
over Snabelen og den fremragende Ende af Støvknappen
for igjen at komme ud. Eftergjor man nu denne Be-
vegelse med en Pensel, saa losnes Snabelens Kappe med
stor Lethed, klæber sig fast til Penslen og medfører
Stovmasserne. Og hvor noie alt er tilpasset til sin Be-
stemmelse, viser sig tydeligt her, idet Stovmasserne kun los-

nes fuldstændigt, naar Penselen føres i Retning af den

fremragende Ende af Stevknappen — den Vei, sont In-
sektet maa tage for at slippe ud; fores den mere indad, saa
følger der kun enkelte Stevklumper med. — Naar nu alt-

saa et Insekt paa sin Vandring ud af Blomsten har faaet
Snabelens Kappe med de vedhengende Stoymasser be-
festet til sit Hoved, og flyver til en anden Blomst, saa
vil Arret vere det første Sted, imod hvilket Stovmassen
vil støde, og der vil den hæftes fast paa Grund af Arrets
Klebrighed. Og det er ikke uden Betydning, at den ydre
Deel af Leben saa let boies ned ved Insektets Vægt, da
der saaledes aabnes saa stor en Indgang til Blomsten, at
Stevmasserne ikke let komme i Berøring med Blomster-
dekket, hvorved en Deel af Stovet vilde gaae til Spilde,
da Stevmasserne meget let senderrives.

Epipactis latifolia (bredbladet Huullebe), som er al-
mindelig i vore Skove, stemmer i det vesenlige overeens
med den forrige Art; kun er Adgangen til Blomsten friere,
idet Lebens ydre Led mangler Elasticitet og Stovknap-
pens Ende ikke rager frem. foran Snabelen, hvorfor Stov-
masserne kunne bortferes uden at denne berøres. Der-
imod afviger Cephalanthera grandiflora (hvidguul
Skovlilie) — som findes i Skove paa Kalkbund og tilhører
en Slægt, der ellers staaer. meget nær ved Epipactis — -
vesenligt fra denne og alle andre, idet Snabelen ganske

297

mangler. Støvkornene ere skilte — ikke forenede i Smaa-
klumper — og kun forbundne ved faa og svage elastiske

Traade. Støvknappene aabne sig for Blomstens Udspring-
ning og skyde Stevmasserne noget frem, saa at de staae
næsten frit som to oprette Seiler, der fortil lene sig imod
Arrets øvre Rand, der naaer op til omtrent 4 af deres
Hoide (Fig. 5). De Stovkorn, som saaledes berøre Arrets
skarpe Rand -- men hverken de høiere eller lavere
staaende — sende allerede for Blomsten
er fuldkommen udsprungen en Mengde
Støvrør dybt ind i Arrets Væv. Der-
efter krummer Arret sig fremad, saa
at Stovseilerne blive heelt frie fra Støv-
knappen og kun holdes oprette af Arret,
hvortil de lene sig og hvormed de ere
forbundne ved Stevrorenes Indtrengen i
Arret. Uden denne Understøttelse vilde

de snart falde om, uagtet Blomstens Stil-

ling er opret og uagtet de ere beskyt- Fig. 5. Cephalan-
tede mod Vinden af Kronbladene og thera Sree

Griffelstotten seet fra

Lebens nedre Deel, der slutte sig tæt Siden, efter at alle Bæ-

ger- og Kronblade ere

sammen om Griffelstotten. Totoni Sicvagilerns
Leben bestaaer, som hos Epipactis, *°°* "em Svar og
Ar.

af*to Dele, og naar Blomsten er fuldt % Stevkappen. p. Stev-
Å masserne. s. Arret.

udviklet, vender den øvre, trekantede

Deel nedad i en ret Vinkel til den nedre Deel, saa at
den danner en god Landingsplads for et Insekt foran en
trekantet Aabning til den næsten rørformede Blomst.
Kort efter at Blomsten er befrugtet, retter denne øvre
Deel af Læben sig igjen op, tilslutter Aabningen og inde-

slutter fuldstændigt Befrugtningsorganerne. Darwin har

298

ikke fundet Honningsaft i Læbens nedre skaalformede
Deel, men antager dog, at der afsondres en saadan.

Cephalanthera grandiflora*) synes altsaa at yde os
det andet Exempel paa stadig Selvbefrugtning hos Orchi-
deerne, eftersom endeel Støvkorn altid befrugte Arret, og
Insekters Medhjælp kunde synes overflødig, da man kunde
tænke sig, at Støvsøilerne ved at falde sammen, vilde
sprede de andre Støvkorn over Arrets Flade, Darwin har
imidlertid godtgjort ved Forsøg, at Støvsøilerne kun und-
tagelsesviis falde sammen, at Støvet altsaa ikke kommer
til Arret, og at de fleste Frø blive golde, naar Blomsterne
udelukkes fra Insekternes Besøg, medens Blomsternes År
i fri Tilstand ere bedækkede med Støvkorn og Søilerne
ganske nedbrudte. Det vilde ogsaa være forunderligt, om
det skulde være uden Hensigt, at Læben en kort Tid
aabner Indgang til Blomsten og siden lukkes,. at Blom-
stens Form netop er saaledes, at et insekt maatte krybe
hen over Arret, og at Støvsøilerne ere stillede saaledes,
at kun nogle faa Støvkorn komme til at virke, medens
store Masser over og under disse bleve ubrugte.

Her synes altsaa at være et sammensat Tilfælde. Her
finder en stadig, men meget ufuldstændig Selvbefrugtning
Sted, der deels tjener til at erstatte Insekternes Hjælp,
hvis den skulde udeblive, deels til at lette Insekternes Ar-
beide ved at holde Støvsøilerne oprette. Men denne
ufuldstændige Befrugtning suppleres ved Besøg af Insek-
ter, der sprede Støvet over Arret af samme Blomst, men
tillige maa føre en Deel med sig til andre Blomster, saa

at her kun tildeels finder en Undtagelse Sted fra den al-

”) De to andre Arter af denne Slægt, som forekomme her i Lan-
det, omtaler Darwin ikke.

haré e SEES FREE SDS

299

mindelige Regel, at den ene Blomst befrugtes af de
andre Blomsters' Støv,

Derimod afgiver Spiranthes autumnalis (Host-
Skrueax) — en her i Landet meget sjelden Art — Exem-
pel paa en Orchidee, der ikke alene nødvendig behøver
Insekters Medhjælp ved Bestøvningen, men hvor desuden
den ene Blomst kun kan bestøves med den andens Sæd-
støv, hvad en kort Beskrivelse af Blomstens Bygning vil

godtgjore. Blomster-
dækket danner et Ror
omkring Griffelstotten,
og paa den Tid, da
Blomsten aabnes, er

Lebens ydre Deel vel
sååledés nedadhoiet, at Fig. 6. Spiranthes autumnalis.
Insekter kunne sætte sig

En moden Blomst efter at Læben (hvis Om-
derpaa , men dens rids er punkteret) har fjernet sig fra Snabelen.
Alle Blade ere bortskaarne, men de øvre Bæger-
blades Stilling ligeledes antydet ved Punkter.

tæt op til Snabelen a. Støvknappen. n. Honninggjemmet. p. Støv-
kornene. r. Snabelen. s. Arret.

indre Deel slutter saa

— her en lang, tynd og

flad Fremragning — og det derunder skraat fremragende
Ar (Fig. 6 r, s), at kun en fiin Rende, foroven dannet af
Snabelens lidt udhulede Forside, forneden af en Huulhed i
Læben, fører ind forbi Arret til Læbens Ende, hvor Hon-
ningsaften opbevares (n). Da Snabelen rager langt frem
over Arret og under Støvknappen — Blomstens Stilling
er nemlig vandret — og altsaa danner en Skillevæg mellem
Arret og Støvet, kan dette ikke befrugte hiint uden saa-
ledes, at Støvmasserne først bortføres fra deres Plads og
derpaa føres ind til Arret; men paa den Tid er Indgangs-
aabningen til Arret altfor snever til at Støvmasserne kunne
bringes derind, Insekterne, som besøge Blomsterne strax

300

efter deres Aabning, kunne derfor vel opsuge Honning-
saften, og idet de trække deres Sugesnabel tilbage, ville
Støvmasserne følge med ud af Blomsten, men de formaae
ikke at bringe dem i Berøring med Arret. Det er først et
Par Dage senere, at Læben fjerner sig saameget fra
Snabelen, at Aabningen bliver stor nok til at tilstede
Støvmasserne, som sidde paa Insektets Sugesnabel, Ad-
gang til Arret. Hvorledes skeer da Bestøvningen? Det
skal strax blive paaviist, men først maa det i Korthed
forklares, hvorledes Støvmasserne, der sidde i Støv-
knappen over Snabelen, kunne bortføres med Insektets
Sugesnabel, der stikkes ind under Snabelen. Denne
bestaaer nemlig af en Slags togrenet Gaffel, og Mellemrum-
met mellem Grenene udfyldes paa Bagsiden (den øverste
Side) af en langstrakt Skive, der er fyldt med klæbrig
Vædske, som i Luften størkner i Løbet af 1 Minut, men
allerede efter 4—5 Sekunders Forløb klæber en Gjen-
stand fast. Paa Forsiden er der en Huulning mellem
Grenene og i denne er Huden saa skrøbelig, at den
brister ved den svageste Berøring og det ikke blot i Huul-
ningen, men langs Klæbeskivens Rande, saa at denne
selv bliver fri og udsveder saamegen Vædske, at den
fastgjøres ved det Legeme, der har foraarsaget Riften og
bortføres med det. Men med denne Klæbeskive følger
da med det samme Støvmasserne, hvis Traade have be-
fæstet sig dertil allerede før Blomstens Aabning, da Støv-
knappens Rum nemlig aabne sig før Blomsten og Støv-
masserne ligge tæt op til Snabelens Ryg. Det er altsaa
indlysende, at en Humlebi — det skal især være disse,
der besøge Spiranthes, — ikke kan føre sin Snabel ind i
den fine Rende, hvis Overside netop er Snabelens Huul-
ning, uden at Støvmasserne ville hæfte sig fast og bort-

301

føres. Men nu er disse Dyrs Fremgangsmaade den, at
de først sætte sig paa den nederste Blomst i Axet, der
er snoet i Spiral, og derpaa krybe opad fra Blomst til
Blomst, idet de følge Spirallinien. De komme altsaa først
til de ældste, længst udsprungne Blomster, sidst til de sidst
udsprungne. Gik de den modsatte Vei, vilde Støvet
spildes. Nu finde de Støvet allerede bortført i de ældre
Blomster; naar de komme til de nys udsprungne, endnu
ikke besøgte Blomster, uddrage da Støvmasserne og flyve
saa til en ny Plante, hvor de begynde paa samme Viis,
og hvor nu Bestøvningen kan gaae for sig i de ældre
Blomster, idet, som ovenfor viist, Læben nu har fjernet
sig tilstrækkeligt fra Arret. I de øvre Blomster hentes
nyt Støv og saaledes fremdeles. Darwin har fanget
Humlebier med indtil 5 Hæfteskiver paa Snabelen. Idet
de saaledes hente Honning til sig selv, sørge de tillige
for at Spiranthes forplanter sig og kan berede Honning
til nye Generationer af Humlebier,

I deu tredie og sidste Afdeling af de indenlandske
Orchideer, af hvilken Darwin omtaler Slægterne: Malaxis,
Listera og Neottia, er ingen Deel af Snabelens Overhud
vedvarende befæstet til Støvmasserne. Hos Malaxis palu-
dosa (Sump-Hjertelæbe) — den mindste af de danske Orchi-
deer — foregaaer Befrugtningen meget let og simpelt,
idet Støvmasserne ved Blomstens Aabning ligge frit —
Støvknappen skrumper nemlig meget tidligt sammen —
og kun med deres øvre spidse Ende støtte sig til Snabe-
lens Top, hvor de”fastholdes af en lille Draabe klæbrig
Vædske; denne Draabe vil et Insekt, der stikker Hoved
elier Snabel ind i Blomsten, nødvendig maatte berøre og

vil saaledes medføre Støvmasserne til andre Blomster,

302

hvor de ville træffe Arret ifølge deres Stilling paa Insæk-
tets Hoved eller Snabel.

Derimod foregaaer Befrugtningen hos de to andre
Slægter paa en meget mærkelig Maade. Det vil være til- i
strekkeligt at omtale
Listera ovata (eg-
bladet Fliglæbe) —
der er temmelig al- i
mindelig i fugtige |
Skove — da de an-
dre sjeldnere Arter i
alt væsenligt stemme

overeens med denne.

Snabelen (Fig. 7,
r), som hvælver sig

ud over Arfladen (S),

er bladagtig, stor og
tynd, foran hvælvet, |
bagtil fordybet og |
paa begge Sider af
den spidse Top noget
udhulet. Støvknap-
pen aabner sig alle-

rede i Knoppen, saa

at Stovmasserne ligge

Fig. 7. Listera ovata. fuldkommen frie i de
Blomsten seet fra Siden; alle Blade bortt
undtagen Leben. oe udsprungne Blom-

a. Stovknappen. col. Griffelstottens Top, l. Leben, ster, lenede til Sna-
n. Lebens. Honningfure p. Stovmassen. r. Snabe- 4

len, s. Arret.: belens Ryg. Denne
boier sig nu lidt frem- og nedad imod Arfladen, hvorved
den fjernes noget fra Stovknappens Spids (a). Naar man
nu bererer Snabelens Spids — om ogsaa blot med et fint

303

Haar — saa springer der øieblikkelig en Draabe klæbrig
Vædske frem af den, der træffer den spidse Ende af Støv-
masserne (p), som hvile paa Snabelens Ryg. 1 Løbet af
2—3 Sekunder størkner denne Draabe og bliver meget
haard. Havde Snabelen ikke i Forveien bøiet sig lidt
frem, vilde den træffe Spidsen af Støvknappen og saaledes
lukke til for Støvet; nu træffer den kun Støvmassernes Spids
og Hovedet af det Insekt, der har bevirket Explosionen, og
fasthæfter saaledes Støvet til dette.

Blomsterne besøges af en stor Mængde Insekter, der
opsuge Honningsaften, som afsondres i en lång, smal Fure
midt i Leben (n), og denne. Fure fortsættes opad den
lange Læbe indtil dens Grund under Arret. Naar Insek-
tet er kommet hertil og løfter Hovedet op for at flyve
bort, vil det træffe Snabelens Spids og frembringe den
ovenfor beskrevne Virkning. Darwin har fanget flere Indivi-
der af Slægterne Hemiteles og Cryptus, der kom ud af
Blomsten med Støvmasserne befæstede til den indre Øierand.
Ganske smaa Insekter, som ikke have Kraft til at bortføre
Støvmasserne, blive undertiden hængende og omkomme.

I det Øieblik, da Snabelen saaledes har udsendt sin
Draabe, krummer den sig endnu mere frem og nedad, saa
at den danner en ret Vinkel med Arret; derved beskytter
den dette, men forhindrer tillige Befrugtningen, saa at
det her ligesom hos Spiranthes er de yngre Blomsters
Støv, der befrugte de ældre Blomsters Ar; thi i Løbet af
nogle Timer eller en Dag, i hvilken Tid Arret udvikler
meget mere Klæbrighed, boier Snabelen sig atter tilbage,
indtil den faaer en ganske opret Stilling, og Adgangen til
Arret bliver fri, saa at Støvmasserne kunne berøre det,
dets Klæbrighed fastholde Støvkornene, sønderrive Traa-

304

dene, hvormed de ere forbundne, og Befrugtningen saa-
ledes gaae for sig.

Darwins Undersøgelser omfatte endnu foruden disse
Slægter en stor Mængde tropiske Orchideer, der frem-
byde mangfoldige Afvexlinger i de Tilpasninger, hvorved
insekterne kunne udføre Bestøvningen. Da hans Materiale
til Undersøgelsen af disse imidlertid har været mindre
rigt end til de indenlandske, og derfor de fleste endnu
trænge til nærmere Undersøgelse, og da næsten alle dette
Tidsskrifts Læsere ville savne Materiale til at eftersee de
beskrevne Forhold i Naturen, hvad Afbildninger kun ufuld-
stændigt kunne erstatte, maa jeg henvise dem, der kunde
ønske en fuldstændigere Kundskab, til Darwins eget Værk.
Jeg skal kun undtagelsesviis omtale en enkelt Slægt, hvor
Befruginingen foregaaer ved en endnu mærkeligere Explo-
sion, end den sidst beskrevne, Slægten Catasetum, der
desuden frembyder den Særegenhed, at Kjønnene ere
adskilte, saa at det kun er undtagelsesviis, at der paa
samme Plante forekommer baade Han- og Hun-Blomster;
og disses Bygning er saa forskjellig, at de have været
henførte til ganske forskjellige Slægter ”).

Hos Catasetum (hvoraf Darwin har undersøgt 3 Arter)
mangler Arret Klæbrighed til at fastholde Støvkornene,
Æggene ere uudviklede og skulle heller ikke i deres
Hjemstavn nogensinde udvikle sig til Frø; Frøkapslen er
ogsaa meget kort og tynd. Derimod er det hos Monachan-

thus Støvmasserne, der ere aldeles rudimentære, deres

* Catasetum tridentatum (Hanblomst, Fig. 8), Monacan-
thus viridis (Hunblomst, Fig 9 A) og Myanthus barbatus
(Tvekjønsblomst, Fig. 9 B) fandtes af R. Schomburgk og senere af
Flere paa en og samme Plante. Til andre Catasetum - Arter
kjender man endnu ikke Hunplanterne. z

305

Rum aabne sig ikke,. og de mangle Snabelens vigtigste
Organer, medens Ar og Æg ere fuldkomment udviklede.
Hos Myanthus endelig findes Bestøvningsredskaberne, Ar
og Æg omtrent ligeligt udviklede. Kun hos denne sidste
kunde altsaa en Befrugtning ved eget Støv foregaae. For
at overføre Støvet fra Catasetum (tridentatum) til Mona-
canthus behøves nødvendigt Insekters Medhjælp, og dertil er
der truffet en høist mærkelig Række af Foranstaltninger.

Fig. 8. Catasetum tridentatum.

A. Blomsten fra Siden; 2 Bægerblade bortskaarne. B. Griffelstøtten opret og
Scet forfra.

a. Stovknappen. an. Snabelens Følehorn. l. Leben. pd. Klæbeskivens Fod.

(Klæbeskiven selv er skjult i det mørke Rum — Argruben — under denne).

Støvmasserne ere ved en temmelig solid og meget
elastisk Fod forbundne med en stor Klæbeskive. Men
denne er utilgængelig for Insekter, da den ligger gjemt i
en Grube (der hvor Arret skulde være) med sin klæbrige
Deel trykket op mod Loftet, saa at Insekter, selv om de
trængte derind, hvortil der ingen Anledning er, ikke vilde
komme i Berøring dermed. Men Klæbeskivens elastiske
Fod (Fig. 8 pd) er boiet over Snabelen og holdes i denne
Stilling som en spændt Bue ved en fiin Hinde, der er
sammenvoxet med to lange, hule Følehorn (an), der ud-

Tredie Række. Il. 21

306

gjøre en Deel af Snabelen og beie sig ned foran Argru-
ben og ere gjemte i Læbens Huulhed. Disse Følehorn ere
i den Grad følsomme, at Berøring med en Børste i deres
Spidse eller et andet Sted paa dem øieblikkeligt foraar-

A. Monacanthus viridis seet fra Siden. B. Myanthus barbatus ligeledes.
a. Støvknappen. an. Følehornene. 1 Leben. s. Arret. sep. Bægerblade.

sager en Bristen af den omtalte Hinde ved deres Grund (uden
at der iøvrigt foregaaer nogen kjendelig Indvirkning paa
Folehornene selv). Derved biiver Klæbeskivens Fod fri, og i
samme Nu retter den boiede Fod sig ud med en saadan
Kraft, at den slynger Klæbeskiven frem og flyver 2—3
Fod ud i Luften medførende Stovmasserne. Klebeski
ven slynges altid foran og vil efter al Sandsynlighed
træffe det Insekt i Hovedet, som ved at gnave paa Læben
og saaledes at berøre Følehornene har bevirket Explosio-
nen. Her hæfter den sig fast, og Støvmassen føres saa-
ledes med, indtil den paa Monachanthus, — hvor hele

307

dette Apparat mangler, men hvor der i Stedet er et klæb-
rigt År — finder en Plads beredt for Støvet. Følehornene
ere det eneste Sted i Blomsten, hvis Berøring befrier
Støvmasserne, men de udføre det ogsaa med Sikkerhed.
I Sandhed, en mærkelig Foranstaltning! Støvmasserne ud-
sendes som Pile, der maa træffe insekterne for saaledes
at bortføres til det Sted, hvor de skulle virke. En sind-
rigere Tilpasning findes vel neppe nogensteds i Naturen.

Det er vist intet forgjæves Haab, Darwin udtaler, at
Meddelelsen af disse Kjendsgjerninger fra Orchideernes
eiendommeligt og mangfoldigt uddannede Familie vil for-
anledige, at mange iagttage de indenlandske Arters Liv
noiere. En Undersøgelse af deres sindrige Indretninger
kan ikke andet end give mange et høiere Begreb om
hele Planteriget og vil være tiltalende saavel for. den, der
anseer alt i det for afhængigt af Naturlove, som for den,
der i alt seer Skaberens umiddelbare Indgriben.

21 *

De menneskelignende Aber: Orang’ens, Chimpansens
og Gibbonernes Levemaade og Naturhistorie.

Efter Huxleys »Evidence as to man’s place in nature«. London. 1864.

Nporgsmaalet om Menneskets Forhold til Dyreriget og
navnlig til Aberne, i systematisk Henseende, har oftere
været paa Bane og er navnlig bleven meget drøftet i de
senere Aar, da Spørgsmaalet om Arternes Oprindelse
og det hele organiske Livs Udviklingshistorie paa Jorden
har sat ikke alene den videnskabelige Verden, men og-
saa den uvidenskabelige (men just ikke ulidenskabelige)
Almeenhed i en vis Bevægelse, Anskuelserne have staaet
saa langt fra hverandre, som vel var muligt; medens
nogle oprettede et eget Rige for Mennesket”), ansaae
andre Slægtskabet mellem Mennesket og Aberne for at
være saa inderligt, at de ikke toge i Betænkning at er-
klære, at Mennesket maatte nedstamme (gjennem den
hypothetiske Darwinske Artsmetamorphose) fra en eller
anden Abeform. Diskussionen herom har havt den gode
Følge, at der derved er kastet en heel Deel Lys over
Forholdet mellem Mennesket og Aberne i zoologisk Hen-
seende; om de Kjendsgjerninger, som i denne Henseende

komme i Betragtning, kan der i al Fald neppe disputeres

”) See dette Tidsskrift 2. Række, 3. Bd

i

MR. DARWIN ON THE DIMOBPHIC CONDITION IN PRIMULA. 77

Cælanthium, limited to two Cape species, differs from Pharna-
ceum as Thylacospermum from Arenaria, by the union of the sepals
at the base into a campanulate tube, round the edge of which are
inserted the stamens, being thus much more decidedly perigynous
than in the rest of the group.

The genera Psammotrophe, Eckl. & Zeyh., and Polpoda, Presl,
with uniovulate cells to the ovary, enumerated by Fenzl among
Mollugineæ, appear to have nothing to distinguish them from true
Phytolaccaceæ. Adenogramma, Presl, is also a Phytolaccaceous
plant allied to Giesekia, where the ovary and fruit are reduced toa
single one-seeded carpel, not compounded of 2 or 3 carpels although
one-seeded as in Paronychiacex. Acrossanthes, on the other hand,
both in habit and character, belongs to the apetalous Ficoidee.

IV. PARONYCHIACEÆ.

Without having sufficiently examined all the genera of this Order
to ascertain their limits with respect to each other, or the order
of their arrangement, we have, however, verified the ordinal cha-
racters in all the following (except Cardionema) :—

1. Corrigiola, Linn. (an exceptional genus in its prominent petals
and alternate leaves); 2. Herniaria, Linn.; 3. Illecebrum, Linn. ;
4. Cardionema, DC.; 5. Pentacena, Bartl.; 6. Paronychia, Juss.
(including Siphonychia, Torr. et Gray, and Anychia, Rich., and
perhaps altogether, with Cardionema and Pentacena, artificial sec-
tions of Illecebrum); 7. Habrosia, Fenzl; 8. Sclerocephalus, Boiss. ;
9. Gymnocarpos, Forsk. ; 10. Pteranthus, Forsk.; 11. Cometes,
Burm. ; 12. Dicheranthus, Webb; 13. Pollichia, Soland. ; 14. Guil-
leminea, H. B. et K.; 15. Mniarum, Forst. ; 16. Scleranthus, Linn. ;
and 17. Lastarriea, A. Gay.

On the Two Forms, or Dimorphic Condition, in the Species of Pri-
mula, and on their remarkable Sexual Relations. By CHARLES
Darwin, M.A., E.R.S., F.LS., &.

A RE LTO

[Read Noy. 21, 1861.]

Tr a large number of Primroses or Cowslips (P. vulgaris and veris)
be gathered, they will be found to consist, in about equal numbers,
of two forms, obviously differing in the length of their pistils and
stamens. Florists who cultivate the Polyanthus and Auricula
are well aware of this difference, and call those which display the
globular stigma at the mouth of the corolla “ pin-headed” or “ pin-
eyed,” and those which display the stamens “thumb-eyed.” I

Mo. Bot. Garden,
1896.

(a

78 MR. O. DARWIN ON THE DIMORPHIC CONDITION

will designate the two forms as long-styled and short-styled. Those
botanists with whom I have spoken on the subject have looked at
the case as one of mere variability, which is far from the truth.
In the Cowslip, in the long-styled form, the stigma projects just
above the tube of the corolla, and is externally visible ; it stands
high above the anthers, which are situated halfway down the tube,

Long-styled. Short-styled.

and cannot be easily seen. In the short-styled form the anthers
are attached at the mouth of the tube, and therefore stand high
above the stigma; for the pistil is short, not rising above halfway
up the tubular corolla. The corolla itself is of a different shape in
the two forms, the throat or expanded portion above the attach-
ment of the anthers being much longer in the long-styled than in
the short-styled form. Village children notice this difference, as
they can best make necklaces by threading and slipping the corollas
of the long-styled flowers into each other. But there are much
more important differences. The stigma in the long-styled plants
is globular, in the short-styled it is depressed on the summit, so
that the longitudinal axis of the former is sometimes nearly double
that of the latter, The shape, however, is in some degree variable ;
but one difference is persistent, namely, that the stigma of the
long-styled is much rougher: in some specimens carefully com-
pared, the papille which render the stigmas rough were in the long-
styled form from twice to thrice as long as in the short-styled.
There is another and more remarkable difference, namely, in the
size of the pollen-grains. I measured with the micrometer many

IN THE SPECIES OF PRIMULA. 79

specimens, dry and wet, taken from plants growing in different
situations, and always found a palpable difference. The measure-
ment is best made with grains distended with water, in which case,

the usual size of the grains from short-styled flowers is seen to be

le of an inch in diameter, and those from the long-styled about

7707 of an inch, which is in the proportion of three to two ; so that
the pollen-grains from the short stamens are plainly smaller than
those from the long stamens which accompany the short pistil.
When examined dry, the smaller grains from the long-styled plants
are seen under a low power to be more transparent than the larger
grains, and apparently in a greater degree than can be accounted
for by their less diameter. There is also a difference in shape,
the grains from the short-styled plants being nearly spherical,
those from the long-styled being oblong with the angles rounded ;
this difference in shape disappears when the grains are distended
with water. Lastly, as we shall presently see, the short-styled
plants produce more seed than the long-styled.

To sum up the differences :—The long-styled plants have a much
longer pistil, with a globular and much rougher stigma, standing
high above the anthers. The stamens are short; the grains of
pollen smaller and oblong in shape. The upper half of the tube
of the corollais more expanded. The number of seeds produced is
smaller.

The short-styled plants have a short pistil, half the length of the
tube of the corolla, with a smooth depressed stigma standing be-
neath the anthers. The stamens are long; the grains of pollen
are spherical and larger. The tube of the corolla is of the same
diameter till close to its upper end. The number of seeds pro-
duced is larger.

I have examined a large number of flowers; and though the
shape of the stigma and the length of the pistil vary, especially
in the short-styled form, I have never seen any transitional grades
between the two forms, There is neyer the slightest doubt under
which form to class a plant. I have never seen the two forms on the
same plant. I marked many Cowslips and Primroses, and found,
the following year, that all retained the same character, as did
some in my garden which flowered out of their proper season in
the autumn. Mr. W. Wooler, of Darlington, however, informs
us that he has seen the early blossoms on Polyanthuses which
were not long-styled, but which later in the season produced flowers
of this form, Possibly the pistils may not in these cases have
become fully developed during the early spring. An excellent

80 MR. C. DARWIN ON THE DIMORPHIC CONDITION

proof of the permanence of the two forms is seen in nursery gar-
dens, where choice varieties of the Polyanthus are propagated by
division; and I found whole beds of several varieties, each consisting
‘exclusively of the one or the other form. The two forms exist in
the wild state in about equal numbers: I collected from several
different stations, taking every plant which grew on each spot,
522 umbels ; 241 were long-styled, and 281 short-styled. No dif-
ference in tint or size could be perceived in the two great masses
of flowers.

1 examined many cultivated Cowslips (P. veris) or Polyanthuses,
and Oxlips ; and the two forms always presented the same differ-
ences, including the same relative difference in the size of the
pollen-grains.

Primula Auricula presents the two forms; but amongst the
improved fancy kinds the long-styled are rare, as these are less
valued by florists, and seldomer distributed. There is a much
greater relative inequality in the length of the pistils and stamens
than in the Cowslip, the pistil in the long-styled form being nearly
four times as long as in the short-styled, in which it is barely
longer than the ovarium ; the stigma is nearly of the same shape
in both forms, but it is rougher in the long-styled, though the
difference is not so great as in the two forms of the Cowslip. In
the long-styled plants the stamens are very short, rising but little
above the ovarium. The pollen-grains of these short stamens from
the long-styled plants, when distended with water, were barely
govo of an inch in diameter, whereas those from the long stamens
of the short-styled plants were barely +77, showing a relative
difference of five to seven. The smaller grains of the long-styled
plants were much more transparent, and before distention with
water more triangular in outline than those of the other form.
In one anomalous specimen with a long pistil, the stamens almost
surrounded the stigma, so that they occupied the position proper
to the stamens of the short-styled form; but the small size of the
pollen-grains showed that these stamens had been abnormally de-
veloped in length, and that the anthers ought to have stood at the
base of the corolla.

In the two forms of Primula Sinensis, the pistil is about twice as
long in the one as in the other. The stigma of the long-styled
varies much in shape, but is considerably more elongated and
rougher than that of the short-styled, the latter being nearly
smooth and spherical, but depressed on the summit. The shape
of the throat of the corolla in the two forms differs as in the Cow-

mice

IN THE SPECIES OF PRIMULA. 81

slip, as does the length of the stamens. But it isremarkable that
the pollen-grains of both forms, wet and dry, presented no differ-
ence in diameter; they vary somewhat in size, as do the pollen-
grains of all the species, but in both forms the average diameter
was rather above 732, of an inch. There is one remarkable dif-
ference in the two forms of this species, namely (as we shall pre-
sently more fully see), that the short-styled plants, if insects be
excluded and there be no artificial fertilization, are quite sterile,
whereas the long-styled produce a moderate quantity of seed. But
when both forms are properly fertilized, the short-styled flowers
(as with Cowslips) yield more seed than the long-styled. Ina lot
of seedlings which I raised, there were thirteen long-styled and
seven short-styled plants.

Of Primula ciliata a long-styled specimen, and of P. ciliata, var.
purpurata, a short-styled specimen, were sent me from Kew by
Prof. Oliver. This case, however, is hardly worth giving, as the
variety purpurata is said* to be a hybrid between this species and
P. auricula ; and the height of the stamens in the one form does not
correspond with the height of the stigma in the other, as they
would have done had they been the same species. There was,
however, the usual difference in the roughness of the stigmas in
the two forms, and the pollen-grains, distended in water, measured

and sæ?
6000 6000
of P. denticulata and P. Piedmontana which were long-styled, and
of P. marginata and nivalis which were short-styled; and the
general character of the organs leaves hardly any doubt on my
mind that these species are dimorphic. In a single flower of P.
Sibirica, however, which was sent me from Kew, the stigma reached
up to the base of the anthers ; so that this species is not dimorphic,
or not dimorphic as far as the length of the pistil and stamens are
concerned, unless indeed this single specimen was anomalous, like
that mentioned of P. auricula.

We thus see that the existence of two forms is very general, if
not universal, in the genus Primula. The simple fact of the
pollen-grains differing in size and outline, and the stigma, in shape
and roughness, in two sets of individuals of the same species, is
curious. But what, it may be asked, is the meaning of these
several differences? The question seems worthy of careful inves-
tigation, for, as far as I know, the use or meaning of dimorphism
in plants has never been explained; hence, I will give my obser-

of an inch in diameter. Single trusses were sent me

* Sweet’s ‘ Flower Garden,’ vol. v. tab. 123.
LINN. PROC —BOTANY, VOL. VI. G

82 MR. C. DARWIN ON THE DIMORPHIC CONDITION

vations in detail, though I am far from supposing that all cases of
dimorphism are alike. The first idea which naturally oceurred
was, that the species were tending towards a dioicous condition ;
that the long-styled plants, with their rougher stigmas, were more
feminine in nature, and would produce more seed; that the short-
styled plants, with their long stamens and larger pollen-grains,
were more masculine in nature. Accordingly, in 1860, I marked
some Cowslips of both forms growing in my garden, and others
growing in an open field, and others in a shady wood, and gathered
and weighed the seed. In each of these little lots the short-styled
plants yielded, contrary to my expectation, most seed. Taking
the lots together, the following is the result :—

| |
No. of No. of | Weight of |

MoE Umbels Capsules meee in |

” | produced. | produced. | grains. |

Short-styled Cowslips 9 33 199 83 |
Long-styled Cowslips 13 51 261 oF |
-l

If we reduce these elements for comparison to similar terms, we
have—

| ] as ] aie ae SR |
| No. of Weight | No. of |W eight No. of Weight |
| Plants. preins | Umbels. | seed. Capsules. a
| Short-styled Cowslips | 10 | 92 | 100 | 251 | 100 a

Long-styled Cowslips | 10 70 | 100 | 178 | 100 34 |

So that, by all the standards of comparison, the short-styled are
the most fertile ; if we take the number of umbels (which is the
fairest standard, for large and small plants are thus equalized), the
short-styled plants produce more seed than the long-styled, in the
proportion of four to three.

In 1861 I tried the result in a fuller and fairer manner. I
transplanted in the previous autumn a number of wild plants

into a large bed in my garden, treating them all alike; the result
was—

No. of | Weight of |

| | Plants | Umbels. seod io |
| | oo j grains. |
prs Se ee |

| Short-styled Cowslips ...| 47 | 173 | 745

| Long-styled Cowslips .,.) 58 208 | 692

IN THE SPECIES OF PRIMULA. 83

These figures, reduced as before, give the following proportions :—

| Number | Weight of| Number | Weight of
| o seed in of seed in

| Plants. grains. | Umbels. | grains.

H J
| Short-styled Cowslips … 100 | 1585 | 100 | 430 |
| Long-styled Cowslips …| 100 1093 100 332

The season was much better this year than the last, and the
plants grew in good soil, instead of in ashady wood or struggling
with other plants in the open field; consequently the actual pro-
duce of seed was considerably greater. Nevertheless we have the
same relative result; for the short-styled plants produced more
seed than the long-styled in the proportion of three to two; but if
we take the fairest standard of comparison, namely, the number of
umbels, the excess is, as in the former case, as four to three.

I marked also some Primroses, all growing together under the
same conditions; and we here see the product :—

Total | lWeight| i f g an

ate of z “of | E | of seed | 8 | IKE We a

ti - Pa Ta |

| ants | EPE, | sules. atn | SE sules. | seed. |

| bs |

Short-styled Primroses| 8 49 40 16 | F 100 40 |
Long-styled Primroses| 9 68 50 | 10 |© 100 | 20 |

The number of Primrose plants tried was hardly sufficient, and
the season was bad ; but we here again see (excluding the capsules
which contained no seed) the same result in a still more marked
manner, for the short-styled plants were twice as productive of
seed as the long-styled plants.

I had, of course, no means of ascertaining the relative fertility of
the two forms of the Chinese Primrose in a natural condition, and
the result of artificial fertilization can hardly be trusted; but six-
teen capsules from long-styled flowers, properly fertilized, produce
9°3 grains’ weight of seed, whereas eight capsules of short-styled
flowers produced 6'1 grains ; so that if the same number, namely,
16 of the latter, had been fertilized, the weight of seed would have
been 122, which would have been nearly in the proportion of four
to three, as in Cowslips. '

Looking to the trials made during two successive yéars on the
large number of Cowslips, and on these facts with regard to com-
mon Primroses and Chinese Primroses, we may safely conclude
that the short-styled forms in these species are more productiye

a 2

84 MR. C. DARWIN ON THE DIMORPHIC CONDITION

than the long-styled forms ; consequently the anticipation that the
plants having largely developed pistils with rougher stigmas, and
having shorter stamens with smaller pollen-grains, would prove to
be more feminine in their nature is exactly the reverse of the
truth. If the species of Primula are tending to become dioicous,
which possibly may be the case, the future hypothetical females
would have short pistils, and the males would have short stamens ;
but this tendency is accompanied, as we shall presently see, by
other conditions of the generative system of a much more singular
nature. Anyhow, the possibility of a plant thus becoming dioicous
by slow degrees is worthy of notice, as the fact would so easily
escape observation.

In 1860 I found that a few umbels of both long-styled and
short-styled Cowslips, which were covered by a net, did not pro-
duce seed, though other umbels on the same plants, artificially fer-
tilized, produced an abundance of seed; and this fact shows that
the mere covering in itself was not injurious. Accordingly, in
1861 I covered up under a similar net several plants just before
they opened their flowers; these turned out as follows :—

|

No.of | |

Doof | umbels | Product of Seed. |

p | produced, | |

Short-styled Ms. 6 24 |13 grains, or 50 seeds.

| Long-styled ...... 0. 18 T | Not one seed. |

Judging from the exposed plants which grew all round in the
same bed, and had been treated in every way exactly the same,
except that they were exposed to the visits of insects, the six short-
styled plants ought to have produced 92 grains’ weight of seed in-
stead of only 13; and the eighteen long-styled plants, which pro-
duced not one seed, ought to have produced above 200 grains’
weight. The production of the 1:3 grain of seed in the smaller
lot was probably due to the action of Thrips or some minute in-
sect. This evidence is sufficient, but I may add that ten pots of
Polyanthuses and Cowslips of both forms, protected from insects
in my greenhouse, did not set one pod, though artificially fertilized
flowers in other pots produced an abundance. So we see that the
visits of insects are absolutely necessary to the fertilization of
Cowslips. As-the exposed plants produced an abundance of seed,
the tendency to a dioicous condition, previously remarked on,
might have been safcly carried on, as we see that there is an effect-

IN THE SPECIES.OF PRIMULA. 85

ive agency already at work which would have carried pollen from
one sex to the other.

What insects habitually visit Cowslips, as is absolutely necessary
for their regular fertility, I do not know. I have often watched
them, but perhaps not long enough ; and only four times I have
seen Humble-bees visiting them. One of these bees was gathering
pollen from short-styled flowers alone, another had bitten holes
through the corolla; and neither of these would have been effective
in the act of fertilization: two others were sucking long-styled
plants. I have watched Primroses more attentively during several
years, and have never seen an insect visit them ; yet from their close
similarity in all essential respects to Cowslips, there can hardly be
a doubt that they require the visits of insects. Hence I am led
to suppose that both Primroses and Cowslips are visited by moths.
All the species which I- have examined secrete plenty of nectar.

In Primula Sinensis, when protected from insects and not arti-
ficially fertilized, the case is somewhat, but not materially, different.
Five short-styled plants produced up to a given period 116 flowers,
which set only seven capsules, whereas twelve other flowers on
the same plants artificially fertilized set ten capsules. Five long-
styled plants produced 147 flowers, and set sixty-two capsules ; so
that this form, relatively to the other, sets a far greater number of
capsules: yet the long-styled protected flowers do not set nearly
so well as when artificially fertilized ; for out of forty-four flowers
thus treated, thirty-eight set. These remarks apply only to the
early setting of the capsules, many of which did not continue
swelling. With respect to the product of seed, seven protected
short-styled plants, which bore about 160 flowers, produced only
half a grain of seed ; they ought to have produced 120 grains: so
that the short-styled plants, when protected from insects, are nearly
as sterile as Cowslips. Thirteen long-styled plants, which bore
about 380 flowers, and which as we have seen set many more cap-
sules, produced 25:9 grains of seed; they ought to have produced
about 220 grains in weight: so that although far less fertile than
the artificially fertilized flowers, yet the long-styled P. Sinensis,
when protected from insects, is nearly twenty-four times as fertile
as the short-styled when protected from insects. The cause of
this difference is, that when the corolla of the long styled plants
falls off, the short stamens near the bottom of the tube are neces-
sarily dragged over the stigma and leave pollen on it, as I saw by
hastening the fall of nearly withered flowers ; whereas in the short-
styled flowers, the stamens are seated at the mouth of the corolla,

86 MR. C. DARWIN ON THE DIMORPHIC CONDITION

and in falling off do not brush over the lowly seated stigma. In
the Cowslip the corolla does not fall off; and both long-styled and
short-styled plants are equally sterile when protected from insects.
It is a rather curious case, that the falling of the corolla, or its re-
maining attached when withered, might have a considerable in-
fluence on the numbers of a plant, during a year unfayourable to
the visits of the proper insects.

In three short-styled plants of Primula auricula, protected from
insects, the flowers which I fertilized produced seed, but those
which were not touched produced none.

In all the species of Primula the pollen readily coheres to any
object. In all that I have observed, though the stamens and pis-
tils differ in length relatively to each other in the different species,
yet, in the two forms of the same species, the stigma of the one
form stands at exactly the same height with respect to the corolla
as the anthers of the other form. If the proboscis of a dead
Humble-bee, or thick bristle, or rough needle be pushed down the
corolla, first of one form, and then of the other, as an insect would
do in visiting the two mingled forms, it will be found that pollen
from the long-stamened form will adhere round the base of the
proboscis, and will be left with certainty on the stigma of the long-
styled form; pollen from the short stamens of the long-styled
form will also adhere a little above the tip of the proboscis, and
some will generally be left on the stigma of the other form. Thus
pollen will be carried reciprocally from one form to the other. In
withdrawing the proboscis from the long-styled form, with pollen
adhering near the tip, there will be a good chance of some being
left on the flower’s own stigma, in which case there will be self-
fertilization ; but this by no means always occurs. In the short-
styled form, on the other hand (and it is important to remember
this), in inserting the proboscis between the anthers situated at
the mouth of the corolla, pollen, as I repeatedly found, is almost
invariably carried down and left on the flower’s own stigma.
Moreover minute insects, such as Thrips, numbers of which I have
observed in Primrose flowers thickly dusted with pollen, could not
fail often to cause self-fertilization. We positively know that the
visits of large insects are necessary to the fertilization of the species
of Primula; and we may infer from the facts just given that these
visits would carry pollen reciprocally from one form to the other,
and would likewise tend to cause self-fertilization, more especially
in the short-styled (7. e. long-stamened) form.

These observations led me to test the potency of the two pol-

IN THE SPECIES OF PRIMULA, 87

lens with respect to the two stigmas in P. veris, Sinensis, and
auricula. In each species four crosses can be tried; namely, the
stigma of the long-styled by its own-form pollen and by that of
the short-styled, and the stigma of the short-styled by its own-
form pollen and by that of the other form. It is necessary to use
and remember two new terms for these crosses: when the long-
and the short-styled stigmas are fertilized by their own-form pol-
len the union is said to be “ homomorphic ;”’ when the long-styled
and short-styled stigmas are fertilized by the pollen of the other
form, the union is “heteromorphic.” I speak of the “own-form
pollen,” because in the following homomorphic unions, in order
to make the experiment perfectly fair, I never placed the pollen
of the same flower on its own stigma, but, to avoid the possible ill
effects of close interbreeding, I always used the pollen from an-
other plant of the same form. In the following experiments all
the plants were treated in exactly the same manner, and were
carefully protected from insects as far as that is possible. I per-
formed every manipulation myself, and weighed the seed in a che-
mical balance. Some of the capsules contained no seed, or only
two or three, and these are excluded in the column marked “ good

pods.” First for P. Sinensis, as the simplest case.

Primula Sinmensis.— TABLE I.

| SB ør ES | hr [ S By Calculation.
BES 3428/8594 | e428
| | SES S833) 883 | W78 | Good f Weight of
| ASEPE EAST | BSE) Pods} geina
Long-styled by own- | | | |
| form pollen (homo- 20 | 18 | 18 | 59 | or as 100 to 45
| _ morphic union) . |
| Long-styled by pollen } | 2
| of short-styled (hete- 24 18 | 16 9:3 | or as 100 to 58
| romorphic union)... } | | |
| Short-styled by own- | | | | | ;
| form pollen (homo- | 7 | 5 4 | 0-9 | or as 100 to 22
| morphic union) .. | «|
| Short-styled by pollen | ie ;
be oE iA (hete- 8 | 8 8 61 | or as 100 to 76
| romorphic union)... |
| Summary : | |
| The two homomorphio | 27 | 93 | 17 | 68
| DE eee bi 32 | 26 | 24 | 154
UNIONS 5. eee ee | | | |

For the sake of comparison, we may reduce these latter figures

as follows :—

88 MR. ©. DARWIN ON THE DIMORPHIC CONDITION

Number of! Number Weight of || Number Weight of
flowers | of good seed in || of good seed in
fertilized.| pods. grains. | pods. grains.
|,
The two homomorphic } 100 63 25 | 100 40
WMIONS SHE SE |
The two heteromor- = ey 64
phic unions .......... 100 75 48 | 00

In the first part of the upper table, the number of flowers fer-
tilized and the simple result is shown; and at the right hand, for
the sake of comparison, the calculated product of the weight of seed
from 100 good pods of each of the four unions is given; showing
that in each case the heteromorphic union is more fertile than the
homomorphic union. Beneath we have a simple summary of the
two homomorphic and the two heteromorphie unions. And lastly,
for the sake of comparison, a calculation bas been made from this
summary ; first, assuming that 100 flowers of both kinds of unions
were fertilized; and then to the right hand, assuming that 100
good pods were produced from both unions. If we compare the
result, we see that the flowers of the two heteromorphic unions
produced a greater number of good pods, and a greater weight of
seed, than the flowers of the two homomorphie unions ; and again
(and this is the fairest element of comparison, for accidents are
thus almost eliminated), that the good pods from the two hetero-
morphic unions yielded more seed, in about the proportion of three
to two, than those from the two homomorphie unions. The dif-
ference in weight from 100 capsules of the two forms is 24 grains,
and this is equal to at least 1200 seeds.

Beneath we have Table IJ. of P. veris, or the Cowslip. The
upper part is exactly the same as in the Table of P. Sinensis, and
we see in each case that the heteromorphic is more fertile than
the homomorphic union. The calculated results from the sum-
mary of the two homomorphic and the two heteromorphic unions
are more complex than with the last species, as I wished to show
that, however we proceed, the general result is the same. We see
that the assumed hundred flowers, heteromorphically fertilized by
the pollen of the other forms, yielded more capsules, more good
capsules, and a greater weight of seed; but I rely little on this, as
some whole umbels perished after being fertilized. The fairest
element of comparison is to take the good capsules alone; and we
here see that the 100 from the two heteromorphic unions yielded
seed which in weight was as 54 to 85 from the 100 good capsules

IN THE SPECIES OF PRIMULA.

89

of the two homomorphie unions,—that is, nearly as three to two,

as in the Chinese Primrose.

Primula veris.—TABLE II.

Sez eee Sey By Calculation.
225 SASE 883/523! Good f Weight of
Eee PETE 23" (228) Poda RES
Long-styled by own-
form pollen (homo- 20 8 5 21 | or as 100 to 42
morphic union) .
Long-styled by pollen
of short-styled (hete- 22 15 14 88 | or as 100 to 62
romorphie union)...
Short-styled by own- |
form pollen ‘(homo- 15 8 6 1:8 | or as 100 to 30
morphic union) .. T
Short-styled by pollen
of long-styled (hete- 13 12 fi 49 | or as 100 to 44
romorphic union)...
Summary :
The two homomorphic p É
MINION SSR NS 39 16 n 32
The two heteromorphic x 95 =
UNIONS 1... } | 35 27 | 25 | 138%

For the sake of comparison, we may reduce these figures as fol-

lows :—

Ss 5 oe 3 oa Y 5 om
| SEE seas E8e leita lass’ £3 a | 2:
ES Bok Ed ERE: SE
| epee BAB pee eg we" |S

| a

| The two ho- |
| momorphic || 100 | 45 | 31 | 11 || 100 | 24 || 100 | 35
| onions …. | |
| The two hete-
| romorphic $| 100 77 71 39 || 100 50 || 100 54
| unions .....

With P. auricula I was unfortunate ; my few seedlings, except
one poor plant, all came up short-styled; and of these plants
several died or became sick, owing to the hot weather and the dif-
ficulty of excluding insects and ventilating the corner of my green-

house enclosed with net.

union, and three from the other.

I finally got only two pods from one
The result is given in the

following table; and, though worth little, we here again see that
the heteromorphic are far more fertile than the homomorphic

unions.

90 MR. C. DARWIN ON THE DIMORPHIC CONDITION

Primula awricula.-—TaBLe III.

| i
Go, w

i So rim os |
| S| Ea A - f

4 u mS] 2S ig Weight of |
| 2532| 323 |274| Good | seed in

a5 CESS Pods. ins.
an ep Baa pe ( grains
a A

|

Short-styled by own-form pol- |
len (homomorphie union) ..

Short styled by pollen of long- }

| styled (heteromorphic union) J

|
|
|
2 1 0-12 | or as 100 to 12 |

3 3 1:50 | or as 100 to 50

Whoever will study these three tables, which give the result
of 134 flowers carefully fertilized and protected, will, I think, be
convinced that in these three species of Primula the so-called
heteromorphic unions are more fertile than the homomorphic
unions. For the sake of clearness, the general result is given in
the following diagram, in which the dotted lines with arrows re-
present how in the four unions pollen has been applied.

Heteromorphic union.
Complete fertility.

7 sooo s (ll
Homomorphic / Ph (dl

union.

j \ Homomorphic
j \ :
l
Incomplete !
i
i
i

` union.
i Incomplete
i

fertility. fertility.

| de

|

| Heteromorphic union.
| Complete fertility.
|

}

|

|

|

|

D

Long-styled Short-styled
Form. Form.

We here have a case new, as far as I know, in the animal and
vegetable kingdoms. We see the species of Primula divided into
two sets or bodies, which cannot be called distinct sexes, for both
are hermaphrodites ; yet they are to a certain extent sexually
distinct, for they require for perfect fertility reciprocal union.
They might perhaps be called sub-dioicous hermaphrodites. As
quadrupeds are divided into two nearly equal bodies of different
sexes, so here we have two bodies, approximately equal in number,

IN THE SPECIES OF PRIMULA. 91

differing in their sexual powers and related to each other like males
and females. There are many hermaphrodite animals which can-
not fertilize themselves, but must unite with another hermaphro-
dite: so it is with numerous plants ; for the pollen is often mature
and shed, or is mechanically protruded, before the flower's own
stigma is ready; so that these hermaphrodite flowers absolutely
require for their sexual union the presence of another hermaphro-
dite. But in Primula there is this wide difference, that one indi-
vidual Cowslip, for instance, though it can with mechanical aid im-
perfectly fertilize itself, for full fertility must unite with another
individual; but it cannot unite with any individual in the same
- manner as an hermaphrodite Snail or Earth-worm can unite with
any other one Snail or Earth-worm; but one form of the Cowslip,
to be perfectly fertile, must unite with one of the other form, just
as a male quadruped must and can unite only with a female.

I have spoken of the heteromorphic union in Primula as result-
ing in full fertility ; and I am fully justified, for the Cowslips thus
fertilized actually gave rather more seed than the truly wild plants
—a result which may be attributed to their good treatment and
having grown separately. With respect to the lessened fertility
of the homomorphic unions, we shall appreciate its degree best by
the following facts. Giirtner has estimated the degree of sterility
of the union of several distinct species*, in a manner which allows
of the strictest comparison with the result of the heteromorphic
and homomorphie unions of Primula. With P. veris, for every hun-
dred seeds yielded by the heteromorphic unions, only sixty-four seeds
were yielded by an equal number of good capsules from the homo-
morphic unions. With P. Sinensis the proportion was nearly the
same—namely, as 100 to 62. Now Gärtner has shown that, on the
calculation of Verbascum lychnitis yielding with its own pollen
100 seeds, it yields when fertilized by the pollen of V. Pheniceum
ninety seeds; by the pollen of V. nigrum, sixty-three seeds; by
that of V. blattaria, sixty-two seeds. So again, Dianthus barbatus
fertilized by the pollen of D. superbus yielded eighty-one seeds,
and by the pollen of D. Japonicus sixty-six seeds, relatively to
the 100 seeds produced by its own pollen. Thus we see—and the
fact is highly remarkable—that the homomorphic unions relatively
to the heteromorphic unions in Primula are more sterile than the
crosses between several distinct species relatively to the pure union
of those species.

The meaning or use of the existence in Primula of the two

+ Versuche iiber die Bastarderzeugung, 1849, s. 216.

92 MR. C. DARWIN ON THE DIMORPHIC CONDITION

forms in about equal numbers, with their pollen adapted for reci-
procal union, is tolerably plain; namely, to favour the intercross-
ing of distinct individuals. With plants there are innumerable
contrivances for this end; and no one will understand the final
cause of the structure of many flowers without attending to this
point. I have already shown that the relative heights of the an-
thers and stigmas in the two forms lead to insects leaving the
pollen of the one form on the stigma of the other; but, at the same
time, there will be a strong probability of the flower’s own pollen
being likewise placed on the stigma. It is perfectly well known
that if the pollen of several closely allied species be placed on the
stigma of a distinct species, and at the same time, or even subse-
quently, its own pollen be placed on the stigma, this will entirely
destroy the simultaneous or previous action of the foreign pollen.
So again if the pollen of several varieties, including the plant’s own
pollen, be placed on the stigma, one or more of the varieties will
take the lead and obliterate the effect of the others: but I have
not space here to give the facts on which this conclusion is
grounded. Hence we may infer as highly probable that, in Pri-
mula, the heteromorphic pollen which we know to be so much the
most effective would obliterate the action of the homomorphic
pollen when left on the flower’s own stigma by insects ; and thus
we see how potent the dimorphic condition of the pollen in Pri-
mula will be in favouring the intercrossing of distinct individuals.
The two forms, though both sexes are present in each, are in
fact dioicous or unisexual. Whatever advantage there may be in
the separation of the sexes, towards which we see so frequent a
tendency throughout nature, this advantage has been here so far
gained, that the one form is fertilized by the other, and conversely ;
and this is effected by the pollen of each form having less po-
tency than that of the other on its own stigma.

Bearing on this view of the final cause of the dimorphism of the
Primulas, there is another curious point. If we look at the right-
hand figures of the four first lines in the previous tables of P. Si-
nensis and veris, we shall see that one of the homomorphic unions,
namely, the short-styled by its own-form pollen, is considerably
more sterile than the other ; and in P. auricula, though here there
is no other homomorphie union as a standard of comparison, this
union is likewise excessively sterile. That the fertility of this
union is really less in a marked degree than in the other three
unions, we have an independent proof in the seeds germinating less
perfectly and much more slowly than those from the other unions.

IN THE SPECIES OF PRIMULA, 93

This fact is the more remarkable, because we have clearly seen
that the short-styled form in the Cowslip in a state of nature is
the most productive of seed. This form bears its anthers close
together at the mouth of the corolla, and I observed long before
I had ascertained the relative fertility of the four unions, in
passing the proboscis of a dead Humble-bee or bristle down the
the corolla, that in this form the flower’s own pollen was almost
certain to be left on its own stigma; and, as I wrote down at the
time, the chance of self-fertilization is much stronger in this than
in the other form. On this view we can at once understand the
good of the pollen of the short-styled form, relatively to its own
stigma, being the most sterile; for this sterility would be the most
requisite to check self-fertilization, or to favour intercrossing.
Hence, also, it would appear that there are four grades of fertility
from the four possible unions in Primula; of the two homomor-
phic unions, as we have just seen, one is considerably more sterile
than the other. In the wild state we know that the short-styled
plants are more fertile than the long-styled ; and we may infer as
almost certain, that in the wild state, when the flowers are visited
by insects, as is absolutely necessary for the production of seed,
and when pollen is freely carried from one form to the other,
that the unions are heteromorphic; if so, there are two degrees of
fertility in the heteromorphic unions, making altogether four
grades of fertility.

Two or three other points deserve a passing notice. The ques-
tion whether the Primrose and Cowslip (P. vulgaris and veris) are
distinct species or varieties has been more disputed and experi-
mented on than in any other plant. But as we now know that
the visits of insects are indispensable to the fertilization of these
plants, and that in all probability the heteromorphic pollen of a
Primrose would be prepotent on the stigma of a Cowslip over the
homomorphic pollen of a Cowslip, the numerous experiments which
have been made, showing that Oxlips appear amongst the seed-
lings of Cowslips, cannot be trusted, as the parent plants do not
appear to have been carefully protected from insects*. I am far
from wishing to affirm that pure Cowslips will not produce Ox-

* Mr.Sidebotham (Phytologist, vol. iii. pp. 703-5) states that he protected his
plants from crossing ; but as he gives in detail all the precautions which he took,
and says nothing about artificial fertilization, we may conclude that he did not
fertilize his plants. As he raised very numerous seedlings, he would have had to
fertilize many flowers, if they had been really well guarded against the visits of
insects. Hence I conclude that his results are not wortby of trust.

94 MR. C. DARWIN ON THE DIMORPHIC CONDITION

lips, but further experiments are absolutely necessary. We may
also suspect that the fact noticed by florists*, that the varieties
of the Polyanthus never come true from seed, may be im part
due to their habitually crossing with other varieties of the Poly-
anthus.

The simple fact of two individuals of the same undoubted species,
when homomorphically united, being as sterile as are many distinct
species when crossed, will surprise those who look at sterility as a
special endowment to keep created species distinct. Hybridizers
have shown* that individual plants of the same species vary in
their sexual powers, so far that one individual will unite more
readily than another individual of the same species with a distinct
species. Seeing that we thus have a groundwork of variability in
sexual power, and seeing that sterility of a peculiar kind has been
acquired by the species of Primula to favour intercrossing, those
who believe in the slow modification of specific forms will natu-
rally ask themselves whether sterility may not have been slowly
acquired for a distinct object, namely, to prevent two forms, whilst
being fitted for distinct lines of life, becoming blended by marriage,
and thus less well adapted for their new habits of life. But many
great difficulties would remain, even if this view could be main-
tained.

Whether or not the dimorphic condition of the Primule has
any bearing on other points in natural history, it is valuable as
showing how nature strives, if I may so express myself, to favour
the sexual union of distinct individuals of the same species. The
resources of nature are illimitable; and we know not why the
species of Primula should have acquired this novel and curious aid
for checking continued self-fertilization through the division of the
individuals into two bodies of hermaphrodites with different
sexual powers, instead of by the more common method of the
separation of the sexes, or by the maturity of the male and female
elements at different periods, or by other such contrivances. Nor
do we know why nature should thus strive after the intercrossing
of distinct individuals. We do not even in the least know the final
cause of sexuality; why new beings should be produced by the union
of the two sexual elements, instead of by a process of partheno-
genesis. When we look to the state in which young mammals
and birds are born, we can at least see that the object gained is

* Mr. D. Beaton, in ‘ Journal of Horticulture, May 28, 1861, pp. 154, 244.
+ Gärtner, Bastarderzeugung, s. 165.

IN THE SPECIES OF PRIMULA. 95

not, as has sometimes been maintained, mere dissemination. The
whole subject is as yet hidden in darkness.

I will now only add that cases of dimorphism, like that of Pri-
mula, seem to be far from rare in the vegetable kingdom, though
they have been little attended to. A large and important class of
analogous facts will probably soon be discovered, Professor Asa
Gray * informs me, that he and Dr. Torrey have described several
Rubiaceous genera, in which some plants have exserted stamens,
and others exserted pistils. “ Mitchella offers an interesting in-
stance of this structure from its relationship, through Wertera, to
Coprosma, one of the few dicecious genera of Rubiacee, and in
which the stamens are elongated in the male flowers and the styles
in the females.’’ The long-styled hermaphrodite flowers of Mit-
chella would probably be found more productive of seed than the
short-styled; in the same way, but in a reversed manner, as in
Primula, the short-styled flowers are more productive than the
long-styled; from which fact I inferred that, if Primula were to
become dicecious, the females would have short pistils and the
males short stamens, these being the corresponding organs neces-
sary for a heteromorphic union with full fertility. In the dicecious
Coprosma, on the other hand, the females have long pistils, and
the males have long stamens. These facts probably show us
the stages by which a dicecious condition has been acquired by
many plants.

Prof. A. Gray also informs me that another Rubiaceous genus
(Knoxia) in India has been described by Dr. Wight, with a
similar structure; and this, I am told, is the case with Cinchona.
Several species of North American Plantago are dimorphic, as is
Rhamnus lanceolatus, as far as its female organs are concerned.
In the Boraginee, Dr. Torrey has observed a strongly marked in-
stance in Amsinckia spectabilis: in some dried flowers sent me by
Prof. Gray, I find that the pistil in the one form is more than
twice as long as in the other, with a corresponding difference in
the length of the stamens; in the short-styled flowers the grains
of pollen, as in Primula, apparently are larger, in the proportion
of nine to seven, than in the long-styled flowers, which have the
short stamens; but the difference can hardly be determined with
safety in dried flowers. In Mertensia alpina, another member of

* See also Prof. Asa Gray’s ‘Manual of the Botany of the N. United States,’
1856, p. 171. For Plantago, see p. 269.

96 MR. C. DARWIN ON THE DIMORPHIC CONDITION IN PRIMULA.

the Boraginee, Prof. Gray finds a new and inexplicable case,—
namely, some specimens with the stamens and pistil sub-exserted,
and other specimens with both organs seated low down the tube of
the corolla. Dr. Torrey and Prof. Gray have designated all such
plants as “ diceciously dimorphous.” In the Labiate, Mr. Bentham
informs me that several species of Ægiphyla, and some of Mentha,
are dimorphic like Primula. The case of Thymus is different, as I
know from my own observations; but I will not here enlarge on
this genus. Again,as I hear from Mr. Bentham, numerous species
of „Oxalis are similarly dimorphic. I can add the genus Linum.
So that we already know of species (generally several in the same
genus) having distinct dimorphic individuals, as far as structure
is concerned, however it may prove in function, in no less than
eight natural orders.

With respect to Linwm, I will not here enter on details, as I in-
tend to try further experiments next summer; but I may state,
that I observed many years ago two forms in Linwm flavum, with
both the pistils and stamens differing in length. In Linum grandi-
florum there are likewise two forms which present no difference in
their male organs, but the pistil and stigmatic surfaces are much
longer in the one form than in the other. The short-styled form,
I have good reason to believe, is highly fertile with its own pollen ;
whether it be more fertile with the pollen of the long-styled form,
I cannot at present say. The long-styled form, on the other hand,
is quite sterile with its own pollen: several plants grew in my
garden, remote from the short-styled plants ; their stigmas were
coloured blue with their own pollen; but although they produced
a vast number of flowers, they did not produce a single seed-
capsule. It seemed a hopeless experiment; but I had so much
confidence from my trials on Primula, that I put a little pollen
from the short-styled plants on the stigmas (already blue with
their own pollen) of twelve flowers on two of the long-styled
plants. From these twelve flowers I got eight remarkably fine
seed-capsules ; the other flowers not producing a single capsule.
The existence of plants in full health, and capable of bearing
seed, on which their own pollen produces no more effect than
the pollen of a plant of a different order, or than so much in-

organic dust, is one of the most surprising facts which I have ever
observed.

ON THE EXISTENCE OF TWO FORMS IN SPECIES OF LINUM., 69

organs are almost concealed by the spathe and bracts. Its nearest
known ally is probably H. rostrata, Ruiz and Payon, a native of
Peru. Dr. Anthoine desires that this noble plant should bear the
name of the Empress of Russia, which I have therefore attached
to it.

Hexiconta Marte, Hook. f. Foliorum vaginis truncum elatum effor-
mantibus, lamina oblonga petiolata ampla, spicis longe pedunculatis
pendulis, spathis crebre dense disticho-imbricatis rachin omnino velan-
tibus late ovato-cymbiformibus recuryis obtusis, floribus bracteis in-
clusis glabratis.

Hab. Betami on the Sinu River (lat, 8° N.), State of Bolivar, in New
Granada (Dr. A. Anthoine).

Truncus 3-4 metr., cum foliis 6 metr., etiam 10-15 centimetr., levis,
viridi-purpureus (Ænth.). Folia oblonga v. lineari-oblonga, obtusa,
3-4 ped, ionga, petiolo æquilonga, viridia. Pedunculus crass. digiti,
curyus, glaber, siccus flexuosus, teres, intus vasibus mollibus farctus.
Spice 1% ped. longe, 3-4 poll. late, lineares, obtusæ, compressæ.
Spathæ 60-80, dense imbricatæ, reflexæ, valde concavæ, late ovato-
cymbiformes, glabræ v. pubescentes, lateribus erectis, basin versus sub-
cordatæ, marginibus undulatis, apice obtusiuscule ; infimæ rostratæ ;
inferiores 1-2 distantes, 4-5 une. longæ, rachin pubescentem non
tegentibus; cæteræ 2-2) unc. long, rachin velantes; superiores in-
feriores amplectentes. Flores rubri (Anth.), in spatha singula 15-20,
bracteis hineari-lanceolatis glabriusculis inclusi, receptaculo brevissimo
in axilla spathæ inserti ; apicibus perianthii tantum exsertis. Bractee
albæ,spatha breviores, ovato-lanceolatie, basi concavæ, exteriores vacuæ,
Pedicelli 3" longi, crassiusculi, villosuli, compressi. Ovarium trigonum,
Perianthium }” long., foliolis extus subtomentosis. Stylus apice in-
curvus. Anthere inclusæ. Drupa cærulea (Anth.), 3-cocca; coecis
oblongis, compressis, basi antice fovea cupulæformi notatis, subrugosis,
osseis, intus subrugosis. Semen erectum; testa membranacea, raphe
annulari circumdata. Albumen subfarinaceum. Embryo axillaris, gra-
cilis, extremitate radiculari paulo crassiore, germinatione foveam cocci
perforante.

On the existence of two forms, and on their reciprocal sexual re-
lation, in several species of the genus Linum. By CHARLES
Darwin, M.A., F.R.S., F.L.S., &c.

AEDE a
[Read February 5, 1863.]

Tar crimson Linum grandiflorum presents two forms, occurring

in about equal numbers, which differ little in structure, but greatly

in function. The foliage, corolla, stamens, and pollen (examined

Mo. Bot. Garden,
1896.

70 MR. DARWIN ON THE EXISTENCE OF TWO FORMS

dry, and distended with water) are alike in both forms. The
difference is confined to the pistil: in the one form, which I will
call “short-styled,”’ the column formed by the united styles, and
the short stigmas, together is about half the length of the whole

pistil in the other and “long-styled” form. A more important -

distinction is, that the five stigmas in the short-styled form diverge
greatly from each other and pass out between the filaments of the
stamens, and thus lie within the tube of the corolla. In the
long-styled form the elongated stigmas stand nearly upright, and
alternate with the anthers. In this latter form the length of the
stigmas varies considerably, their upper extremities projecting
even a little above the anthers, or reaching up only to about their
middle. Nevertheless there is never the slightest difficulty in
distinguishing between the two forms; for, besides the difference
in divergence, the stigmas of the short-styled form never reach
even to the bases of the anthers. In the short-styled, the papilla
on the stigmatic surfaces are shorter, darker-coloured, and more
crowded together than in the long-styled form: but these differ-
ences seem due merely to the shortening of the stigma; for in the
varieties of the long-styled form with shorter stigmas, the papille
are more crowded and darker-coloured than in those with the
longer stigmas. Considering the slight and variable differences
between the two forms of this Linum, it is not surprising that
they have been hitherto overlooked.

In 1861 I had eleven plants growing in my garden, eight of
which were long-styled, and only three short-styled. Two very
fine long-styled plants grew in a bed a hundred yards off, and
separated from the others by a screen of evergreens. I marked
twelve flowers, and put on their stigmas a little pollen from the
short-styled plants. The pollen of the two forms is, as stated,
identical in appearance; the stigmas of the long-styled flowers
were already thickly covered with their own pollen—so thickly
that I could not find one bare stigma; and it was late in the
season, namely, September 15th. Altogether, to expect any result
from this trial seemed almost childish, From my experiments,
however, on Primula, which have been laid before this Society

(‘ Journal,’ vol. vi. p. 77), I had faith, and did not hesitate to make’

the trial, but certainly I did not anticipate the full result. The
germens of these twelve flowers all swelled, and ultimately six fine
capsules (the seed of which germinated this year) and two poor
capsules were produced; only four capsules shanked off, These

IN SEVERAL SPECTES OF THE GENUS LINUM. 71

two plants produced, before and after and at the time of the trial,
a vast number of flowers, but the germens of not even one swelled.
All these flowers, though their stigmas were so densely covered
with their own pollen, were absolutely barren.

The nine other plants, six long-styled and three short-styled,
grew in the beds of the same flower-garden. Four of the long-
styled produced no seed-capsules; one produced two; but the re-
maining long-styled plant grew so close to a short-styled plant
that their branches touched, and this produced twelve capsules,
but they were poor. The case was different with the short-styled
plants. The plant which grew in juxtaposition with the long-
styled plant produced ninety-four imperfectly fertilized capsules
containing a multitude of bad seeds, with a moderate number of
good seeds. The two other short-styled plants grew in a single
clump, and were very small, being partly smothered by other
plants; they did not stand very close to any long-styled plants,
yet they yielded together nineteen capsules. These facts seem to
show that the short-styled plants are far more fertile with their
own pollen than the long-styled. We shall immediately see that
this is the case in a slight degree. But I suspect that in this
instance the difference in fertility between the two forms was in
part due to a distinct cause. I repeatedly watched the flowers,
and only once saw a humble-bee momentarily alight on one, and
then fly away, as if it were not to its taste. If bees had visited
the several plants, there cannot be a doubt that the four long-

` styled plants which did not produce a single capsule would have

borne an abundance. But several times I saw small diptera suck-
ing the flowers; and these insects, though not visiting the flowers
with anything like the regularity of bees, would carry a little
pollen from one form to the other, especially when growing close
together; and the stigmas of the short-styled plants, diverging
within the tube of the corolla, would be more likely than the up-
right stigmas of the long-styled to receive a small quantity of
pollen when brought by small insects. From the much greater
number of long-styled than of short-styled flowers in the garden,
evidently the short-styled would be more likely to receive some
pollen from the long-styled, than the long-styled from the short-
styled.

In 1862 I raised thirty-four plants of this Linum in a hotbed ;
and these consisted of seventeen long-styled and seventeen short-
styled forms. Seed sown later in the flower-garden yielded seven-
teen long-styled and twelve short-styled forms. These facts justify

72 MR. DARWIN ON TITE EXISTENCE OF TWO FORMS

the statement that the two forms are produced in about equal
numbers. The first thirty-four plants were kept under a net
which excluded insects. I fertilized heteromorphically fourteen
long-styled flowers with pollen from the short-styled, and got
eleven fine seed-capsules ; these contained on an average 8'6 seeds
per capsule, but only 5-6 were apparently good. It may be well to
state that ten seeds is the maximum possible production for a
capsule, and that our climate cannot be very favourable to this
North-African plant. On three occasions I fertilized homomor-
phically the stigmas of altogether nearly a hundred flowers (but
did not separately mark them) with their own pollen, but taken
from separate plants, so as to prevent any possible ill effects
from close interbreeding ; and many other flowers were produced,
which, as before stated, would get plenty of their own individual
pollen; yet from all these flowers, borne by the seventeen long-
styled plants, only three capsules were produced; one of these in-
cluded no seed, and the other two together gave only five good
seeds. Nor do I feel at all sure that this miserable product of the
two half-fertile capsules from the seventeen plants, each of which
must have produced at least fifty or sixty flowers, is really the re-
sult of their fertilization by their own pollen; for I made a great
mistake in keeping the two forms under the same net, with their
branches often interlocking, and it is surprising that a greater
number of flowers were not accidentally fertilized,

Of the short-styled flowers I fertilized heteromorphically twelve
with the pollen of the long-styled (and to make sure of the result `
T previously castrated the majority), and obtained seven fine seed-
capsules. These included an average of 7-6 seeds, but of apparently
good seed only 4'3 per capsule. At three separate. times I ferti-
lized homomorphically nearly a hundred flowers with their own-
form pollen, taken from separate plants; and numerous other
flowers were produced, many of which must have received their
own pollen, From all these flowers borne on the seventeen plants,
only fifteen capsules were produced, of which only eleven con-
tained any good seed, on an average 4'2 per capsule. As remarked
in the case of the long-styled plants, some even of these capsules
were perhaps the product of a little pollen accidentally fallen
from the flowers of the other form. Nevertheless the short-
styled plants seem to be slightly more fertile with their own
pollen, in the proportion of fifteen capsules to three, than the
long-styled: the real proportional excess in fertility is probably
a little greater, as the short-styled flowers, when not disturbed, do

IN SEVERAL SPECIES OF THE GENUS LINUM. 73

not so surely receive their own pollen as do the long-styled. The
greater self-fertility of the short-styled flowers was, as we have
seen, also shown by the plants left to themselves, and but sparingly
visited by insects, in the flower-garden in 1861, and likewise by
those raised in 1862.

The absolute sterility (judging from the experiments of 1861,
and which is hardly contradicted by those of 1862) of the long-
styled plants with their own-form pollen led me to examine into
its apparent cause; and the result is so curious that it will be
worth while to give most of the experiments in detail. These ex-
periments were tried on fresh plants, grown in pots and brought
successively into the house.

First. I placed pollen from a short-styled flower on the
five stigmas of a long-styled plant, and after thirty hours found
them deeply penetrated by a multitude of pollen-tubes, far too
numerous to be counted ; the stigmas had become discoloured and
twisted. I repeated this experiment on another flower, and in 18
hours found the stigmas penetrated by a multitude of long pollen-
tubes. All this is what might have been expected, as this is a fertile
or heteromorphic union. I likewise tried the converse experiment,
and placed pollen from a long-styled flower on the stigmas of a
short-styled flower, and in 24 hours found the stigmas discoloured,
twisted, and penetrated by numerous pollen-tubes ; and this, again,
is what might have been expected, as this is a fertile or hetero-
morphic union.

Secondly. I placed pollen of a long-styled flower on all five
stigmas of a long-styled flower on aseparate plant: after 19 hours
I rigorously dissected the stigmas, and found only a single pollen-
grain which had emitted a very short tube. To make sure that
the pollen was good, I took in this case, and in most other cases,
pollen either from actually the same anther or from the same
flower, and proved it to be good by placing it on the stigma of a
short-styled “plant, and seeing numerous pollen-tubes emitted.

Thirdly. Repeated last experiment, and placed own-form pollen
on all five stigmas of a long-styled flower; and, after 193 hours,
not one single grain had emitted its tube.

Fourthly. Repeated the experiment, with the same result after
24 hours.

Fifthly. Repeated last experiment, and, after leaving pollen on
for 19 hours, put an additional quantity of own-form pollen on
all five stigmas. After an interval of exactly three whole days,
I rigorously examined the stigmas, which, instead of being dis-

LINN. PROC.—BOTANY, VOL, VII. G

74 MRE. DARWIN ON THE EXISTENCE OF TWO FORMS

coloured and twisted, were straight and fresh-coloured ; and only
one grain had emitted quite a short tube, which could be drawn
out of the stigmatic tissue without being ruptured.

The following experiments are more striking :—

Sizthly. I placed own-form pollen on three of the stigmas of a
long-styled flower, and pollen from a short-styled flower on the
other two stigmas. After 22 hours these two stigmas were dis-
coloured, and slightly twisted, and penetrated by the tubes of
numerous pollen-grains: the other three stigmas, covered with
their own-form pollen, were fresh, and all the pollen-grains were
loose ; but I did not dissect the whole stigma rigorously.

Seventhly. Experiment repeated in the same manner, with the
same result.

Eighthly. Experiment repeated, but the stigmas were carefully
examined after an interval of only 54 hours. The two stigmas with
pollen from a short-styled flower were penetrated by innumerable
tubes; but these were as yet short, and the stigmas themselves
were not at all discoloured. The three stigmas covered with their
own-form pollen were not penetrated by a single pollen-tube.

Ninthly. Put pollen of short-styled on one stigma, and own-
form pollen on the other four stigmas ; after 24 hours, found the one
stigma somewhat discoloured, and twisted, and penetrated by many
long tubes: the other four stigmas were quite straight and fresh ,
but on dissecting their whole lengths I found that three pollen-
grains had protruded quite short tubes into the tissue.

TLenthly. Repeated the experiment, with the same result after 24
hours, excepting that only two own-form grains had penetrated the
stigmatic tissue with their tubes, to a very short depth: the one
stigma, which was deeply penetrated by a multitude of tubes from
the short-styled pollen, presented a conspicuous difference in com-
parison with the other four straight and bright pink stigmas, in
being much curled, half-shrivelled, and discoloured.

I could add a few other experiments ; but those now given amply
suffice to show that the pollen-grains of a short-styled flower placed
on the stigmas of a long-styled flower emit a multitude of tubes
after an interval of from five to six hours, and penetrate the tissue
ultimately to a great depth, and that after twenty-four hours the
stigmas thus penetrated change colour, become twisted, and appear
half-withered. On the other hand, the pollen-grains of the long-
styled flowers placed on their own stigmas, after an interval of a
day, or even three days, do not emit their tubes, or at most only
three or four grains out of a multitude emit their tubes ; and these

IN SEVERAL SPECIES OF THE GENUS LINUM. 75

apparently never penetrate the stigmatic tissue deeply, and the
stigmas themselves do not become discoloured and twisted.

This seems to me a remarkable physiological fact. The pollen-
grains of the two forms are undistinguishable under the micro-
scope ; the stigmas differ only in length, degree of divergence, and
in the size, shade of colour, and approximation of their papillæ, these
latter differences being variable and apparently simply due to the
elongation of the stigma. Yet we plainly see that the two pollens
and the two stigmas are widely dissimilar in action—the stigmas of
each form being almost powerless on their own pollen, but causing,
through some mysterious influence, by simple contact (for I could
detect no viscid secretion), the pollen-grains of the opposite form
to protrude their tubes. It may be said that the two pollens and
the two stigmas by some means mutually recognize each other.
Taking fertility as the criterion of distinctness, it is no exaggera-
tion to say that the pollen of the long-styled Linum grandiflorum
(and conversely of the other form) has been differentiated, with
respect to the stigmas of all the flowers of the same form, to a
degree corresponding with that of distinct species of the same
genus, or even of species of distinct genera.

Linum perenne.—The dimorphism is here more conspicuous, and
has been noticed by several authors. In the long-styled form the
pistil is nearly twice as long as in short-styled ; in the latter the
stigmas are smaller and, diverging more, pass out between the fila-
ments of the stamens. I could detect no difference in the size of
the stigmatic papille ; in the long-styled form alone the stigmatic
surfaces turn round so as to face the circumference of the flower:
but to this point we shall presently return. Differently from what
occurs in L. grandiflorum, the long-styled flowers have stamens
hardly more than half the length of those of the short-styled. The
size of the pollen-grains is rather variable ; after some doubt, I have
come to the conclusion that there is no uniform difference between
the pollen of the two forms. The long stamens in the short-styled
form project to some height above the corolla, and, apparently from
exposure to the light, the filaments are coloured blue. These longer
stamens correspond in height with the lower part of the stigmas
of the long-styled flowers; and the shorter stamens of the latter
form correspond in the same manner in height with the shorter
stigmas of the short-styled flowers.

F raised from seed twenty-six plants, which proved to be twelve
long-styled and fourteen short-styled. They flowered well, but
were not large plants. As I did not expect them to flower so

a2

76 MR. DARWIN ON THE EXISTENCE OF TWO FORMS

soon, I did not transplant them, and they unfortunately grew with
their branches closely interlocked. All the plants were covered
by a net, excepting one of each form. First, of the long-styled
flowers, twelve were homomorphically fertilized by their own-form
pollen, taken in every case from a separate plant; and not one
flower set a seed-capsule: twelve other flowers were heteromor-
phically fertilized by pollen from short-styled flowers ; and they set
nine pods, each including on an average seven good seeds: as
before, ten seeds is the maximum possible production. Secondly,
of the short-styled flowers, twelve were homomorphically fertilized
by own-form pollen, and they yielded one capsule, including only
three good seeds; twelve other flowers were’ heteromorphically
fertilized by pollen of long-styled flowers, and these produced nine
capsules, but one was bad; the eight good capsules contained on
an average exactly eight good seeds each.

The many flowers on the eleven long-styled plants under the
net, which were not fertilized, produced only three capsules
(including 8, 4, and 1 good seeds); whether, owing to the inter-
locking of the branches, these accidentally received pollen from
the other form, I will not pretend to conjecture. The single long-
styled plant which was uncovered, and grew close by the uncovered
short-styled plant, produced five good pods ; but it was a very poor
and small plant.

The flowers borne on the thirteen short-styled plants under the
net, which were not fertilized, produced twelve capsules (containing
5'6 seeds on average) : as some of these capsules were very fine, and
five were borne on one twig, I suspect that they had been visited
by some minute insect which had accidentally got under the net
and had carried pollen from the other form. The one uncovered
short-styled plant yielded exactly the same number of capsules,
namely, twelve. :

From these facts we have some evidence, as in the case of Z.
grandiflorum, that the short-styled plants are in a very slight
degree more fertile with their own pollen than are the long-styled
plants. And we have the clearest evidence, from the result of the
forty-eight flowers artificially fertilized, that the stigmas of each
form require pollen from the stamens of corresponding height
produced by the opposite form.

In contrast with the case of L. grandiflorum, it is a singular fact
that the pollen-grains of both forms of Z. perenne when placed on
their own-form stigmas, though not causing fertility, yet emit their
tubes; and these tubes I found, after an interval of eighteen

IN SEVERAL SPECIES OF THE GENUS LINUM. 77

` hours, had penetrated the stigmatic tissue, but to what depth I

did not ascertain, In this case the inaction of the pollen-grains on
their own stigmas must be due either to the tubes not reaching
the ovules, or reaching them and not efficiently acting on them.
In the case of Lythrum Salicaria, which I hope at some future
time to lay before the Society, there are three distinct forms, each
of which produces two kinds of pollen; but neither pollen, when
placed on its own stigma, causes fertility, except occasionally and
in a very moderate degree ; yet the pollen-tubes in each case freely
penetrate the stigmatic tissue.

The plants of L. perenne and of L. grandiflorum grew, as stated,
with their branches interlocked, and with scores of flowers of the
two forms close together; they were covered by an open net,
through which the wind, when high, passed; and such minute in-
sects as Thrips could not, of course, be excluded; yet we have
seen that the utmost possible amount of accidental fertilization on
seventeen long-styled plants in the one case, and on eleven plants
in the other case, was the production, in each, of three poor cap-
sules ; so that we may infer that, when the proper insects are ex-
cluded, the wind does hardly anything in the way of carrying
pollen from plant to plant. I allude to this fact because botanists,
in speaking of the fertilization of plants or of the production of
hybrids, often refer to the wind or to insects as if the alternative
were indifferent. This view, according to my experience, is en-
tirely erroneous. When the wind is the agent in carrying pollen,
either from one separated sex to the other, or from hermaphrodite
to hermaphrodite (which latter case seems to be almost equally
important for the ultimate welfare of the species, though occurring
perhaps only at long intervals of time), we can recognize structure
as manifestly adapted to the action of the wind as to that of
insects when they are the carriers. We see adaptation to the
wind in the incoherence of the pollen, in the inordinate quantity
produced (as in the Conifére, Spinage, &c.), in the dangling anthers
well fitted to shake out the pollen, in the absence or small size of
the perianth or in the protrusion of the stigmas at the period of
fertilization, in the flowers being produced before they are hidden
by the leaves, in the stigmas being downy or plumose (as in the
Graminew, Docks, and other plants) so as to secure the chance-
blown grains. In plants which are fertilized by the wind, the
flowers do not secrete nectar, their pollen is too incoherent to be
easily collected by insects, they have not bright-coloured corollas
to serve as guides, and they are not, as far as I have seen, visited

78 MR. DARWIN ON THE EXISTENCE OF TWO FORMS

by insects. When insects are the agents of fertilization (and this `
is incomparably the more frequent case both with plants having
separated sexes and with hermaphrodites), the wind plays no part,
but we see an endless number of adaptations to ensure the safe
transport of the pollen by the living workers. We can recognize
these adaptations most easily in irregular flowers ; but they do not
the less occur in perfectly regular flowers, of which those of Linum
offer an instance, as I will almost immediately endeavour to show.

I have already alluded to the rotation of each separate stigma in
the long-styled form alone of Linum perenne. In the other species
examined by me, and in both forms when the species are dimor-
phic, the stigmatic surfaces face the centre of the flower, and the
furrowed backs of the stigmas, to which the styles are attached, face
the circumference. This is the case, in the bud, with the stigmas of
the long-styled flowers of L. perenne. But by the time the flower
in this form has expanded, the five stigmas, by the torsion of that
part of the style which lies beneath the stigma, twist round and
face the circumference. I should state that the five stigmas do
not always perfectly turn round, two or three often facing only
obliquely towards the circumference. My observations were made
during October ; and it is not improbable that earlier in the season
the torsion would have been more perfect; for after two or three
cold and wet days the movement was very incomplete. The flowers
should be examined shortly after their expansion ; for their dura-
tion is brief, and, as soon as they begin to wither, the styles be-
come spirally twisted together, and the original position of the
parts is lost.

He who will compare the structure of the whole flower in both
forms of L. perenne and grandiflorum, and, I may add, of L. flavum,
will, I think, entertain no doubt about the meaning of this torsion
of the styles in the one form alone of L. perenne, as well as the
meaning of the divergence of the stigmas in the short-styled forms
of all three species. It is absolutely necessary, as we now know,
that insects should reciprocally carry pollen from the flowers of
the one form to those of the other. Insects are attracted by five
drops of nectar, secreted exteriorly at the base of the stamens, so
that to reach these drops they must insert their proboscides outside
the ring of broad filaments, between them and the petals. In the
short-styled form of the above three species, the stigmas face the
axis of the flower; and had the styles retained their original up-
right and central position, not only would tne stigmas have pre-
sented their backs to insects as they sucked the flowers, but they

IN SEVERAL SPECIES OF THE GENUS LINUM. 79

would have been separated from them by the ring of broad fila-
ments, and could never have been fertilized. As it is, the styles
diverge greatly and pass out between the filaments. The stigmas,
being short, lie within the tube of the corolla; and their papillous
faces, after the divergence of the styles, being turned upwards are
necessarily brushed by every entering insect, and thus receive the
required pollen.

In the long-styled form of L. grandiflorum, the parallel anthers
and stigmas, slightly diverging from the axis of the flower, project
only a little above the tube of the somewhat concave corolla; and
they stand directly over the open space leading to the drops of
nectar. Consequently when insects visit the flowers of either
form (for the stamens in this species occupy the same position in
both forms), they will get their proboscides well dusted with the
coherent pollen. As soon as the insect inserts its proboscis to a
little depth into the flower of the long-styled form, it will neces-
sarily leave pollen on the faces and margins of the long stigmas ;
and as soon as the insect inserts its proboscis to a rather greater
depth into the short-styled flowers, it will leave pollen on their
upturned stigmatic surfaces. Thus the stigmas of both forms
will indifferently receive the pollen of both forms; but we know
that the pollen alone of the opposite form will produce any effect
and cause fertilization.

Long-styled form of L. perenne, var. Austriacum, with the petals and calyx
remoyed on the near side.
In the case of L. perenne, affairs are arranged a little more per-
fectly ; for the stamens in the two forms stand at different heights,

80 MR. DARWIN ON THE EXISTENCE OF TWO FORMS

and pollen will adhere to different parts of an insect’s body, and
will generally be brushed off by the stigmas of corresponding
height, to which stigmas each kind of pollen is adapted. In this
species, the corolla is flatter, and in the one form the stigmas and
in the other form the anthers stand at some height above the
mouth of the corolla*. These longer stigmas and longer stamens
do not diverge greatly ; hence insects, especially rather small ones,
will not insert their proboscides between the stigmas or between
the anthers, but will strike against them, at nearly right angles,
with the backs of their head or thorax. Now, in the long-styled
flowers of L. perenne, if each stigma had not rotated on its axis,
insects in visiting them would have struck their heads against the
backs of the stigmas; as it is, they strike against the papillous
fronts of the stigmas, and, their heads being already charged with
the proper coherent pollen from the stamens of corresponding
height borne by the flowers of the other form, fertilization is per-
fectly effected.

Thus we can understand the meaning of the torsion of the
styles in the long-styled flowers alone, as well as their divergence
in the short-styled flowers.

One other point is worth a passing notice. In botanical works
many flowers are said to be fertilized in the bud. This rests
solely, as far as I can discover, on the anthers opening in the bud ;
no evidence is adduced that the stigma is at this period mature,
or that, if then penetrated by pollen-tubes, it is not subsequently,
after the expansion of the flower, acted on by pollen brought from
other flowers. In the case of Cephalanthera grandiflora I have
shownt by experiment that insufficient precocious self-fertiliza-
tion, together with subsequent full fertilization, is the regular
course of events. The belief that flowers of any plant are habitu-
ally fertilized in the bud, or are perpetually self-fertilized, is a
most effectual bar to really understanding their structure. I am
far from wishing to say that some flowers, in certain seasons, are
not fertilized in the bud: I bave reason to believe that some
flowers are frequently fertilized without expanding ; but my ob-
servations lead me to disbelieve that this is ever the invariable

* I neglected to get drawings made from fresh flowers of the two forms.
Mr. Fitch has made the above sketch of a long-styled flower from dried speci-
mens and published engravings : his well-known skill ensures accuracy in the
proportional size of the parts ; and I believe their relative position is true.

+ Fertilization of Orchids, p. 108.

IN SEVERAL SPECIES OF THE GENUS LINUM. 81

course with all the flowers of any species whatever. As it is dif-
ficult to prove without troublesome experiments the falsity of the
belief of regular fertilization in the bud, I here notice this subject.
An estimable and laborious obseryer*, resting his belief on the
usual kind of evidence, states that in ZL. Austriacum (which is
dimorphic and is considered by Planchon as a variety of L,
perenne) the anthers open the evening before the expansion of the
flowers, and that the long-styled stigmas are then almost always
fertilized. He asks whether this precocious fertilization in the
several species of Linum and in other plants is not one cause of
the short duration of their flowers. Now we know positively that,
so far from Linum perenne being fertilized by its own pollen in
the bud, its own pollen is as powerless on the stigma as so much
inorganic dust.

Linum flavum.—tTo recur to our more immediate subject, in
the long-styled form of this species the pistil is nearly twice as
long as in the short-styled form ; and the stigmas are longer with
the papille coarser. In the short-styled form the stigmas diverge
and pass out between the filaments. The stamens in the two forms
differ in height, and, what is singular, the anthers of the longer
stamens are shorter ; so that in the short-styled form both stigmas
and anthers are shorter than in the other form. The pollen of
the two forms does not differ. I have not been able to try any
experiments on this species; but a careful observer, Mr. W. C.
Crocker, intends proving their reciprocal fertility next summer.
As this plant is propagated by cuttings, I have generally found
that all the plants in the same garden belong to the same form.
On inquiry I have never heard of its seeding in this country ; but
to anyone wishing to raise seedlings, in all probability the path is
now open, namely, by carrying pollen from one form to the other.

I have now shown that three species of Linum are dimorphic,
besides several races of L. perenne, esteemed by some botanists to
be distinct species, such as L. montanum, L. Sibiricum, and L. Aus-
triacum. According to Vauchert, L. Gallicum, L. maritimum, and
L. strictum are in the same manner dimorphic, as likewise is, ac-
cording to Planchont, L. salsoloides. This latter botanist is the
only one who seems to have been struck with the importance of
the subject ; and he acutely asks whether this dimorphism has not
some influence on the manner of fertilization. We thus know of

* Etudes sur la Géograph. Bot., par Prof. H. Lecoq, 1856, tom. v. p. 325.

+ Hist. Physiolog. des Plantes d'Europe, 1841, tom. i. p. 401.
t Hooker’s London Journ. of Botany, 1848, vol. vii. p. 174.

82 ON THE EXISTENCE OF TWO FORMS IN SPECIES OF LINUM.

seven dimorphic species of Linum; but as this structure has been
overlooked in such common garden-flowers as L. grandiflorum and
L. flavum, it is probably of frequent occurrence.

All the species, however, are certainly not thus characterized. I
have examined many specimens of L, catharticum, and found in
all that the stamens and stigmas were of nearly equal height and
the same in all the plants. So, again, I looked, near Torquay, at
many flowers of the wild L, usitatissimum or angustifolium (1
know not which), and there was no trace of dimorphism. Again,
I raised 111 plants from seed sent me from Kew, incorrectly
named L, Austriacum; the plants were tall and straight, having a
rather different aspect from the wild species seen at Torquay, with
extremely fugacious blue flowers: in all these plants the stigmas
stood on a level with the anthers or projected a very little above
them. I protected the flowers from insects ; but every one of the
111 plants produced plenty of seed. I mention this fact because it
had occurred to me that possibly a species might be dimorphic in
function, though not in structure.

Lastly, Linwm Lewisii, which is ranked by Planchon as a variety
of L. perenne, but which, now that we know the meaning of re-
ciprocal dimorphism, surely deserves specific honours, must not be
passed over. According to Planchon*, the same plant bears some
flowers with anthers and stigmas of the same height, and others
with styles either longer or shorter than the stamens; so that the
same individual plant is trimorphic. This, as far as I know, is a
unique case. From analogy we may pretty safely predict the
function of the three kinds of flowers: those with stigmas’ and
anthers of the same height will be self-fertile ; those with these
organs of unequal height will require reciprocal fertilization, A
plant of L. grandiflorum or of the other dimorphic species, grow-
ing by itself, could no more perpetuate its race than could one
sex of a dicecious plant, nor could any number of plants without
the aid of insects. A single plant of Linwm Lewisii, on the other
hand, in all probability could propagate itself, even if no insects
were present, as probably sometimes occurs in its Arctic home.
If insects visited the plant, the flowers which were dimorphic
would be fertile one with another or with those on any neighbour-
ing plant. Thus the plant would receive the advantage of a cross.

* Hooker’s London Journ. of Botany, 1848, vol. vii. p. 175. It is not im-
probable that the allied genus Hugonia is dimorphic ; for (p. 525) one species is
described “staminibus exsertis ;” another has “stamina 5, majora, stylos longe
superantia ;” and another is furnished “ stylis staminibus longioribus.”

—

FORM OF THE VASCULAR FASCICULI IN BRITISH FERNS. 83

That this is an advantage, and is one great end gained by reciprocal
dimorphism, I can entertain no doubt. That in some cases this
dimorphism may be a step towards a complete separation of the
sexes, I will not dispute; but good reasons could be assigned
to show that there is no. necessary connexion between reciprocal
dimorphism and a tendency to dicecious structure. Although good
is gained by the inevitable crossing of the dimorphic flowers, yet
numerous other analogous facts lead me to conclude that some
other quite unknown law of nature is here dimly indicated to us.

On the Form of the Vascular Fasciculi in certain British Ferns.
By Arruvur H. Cuvrcu, B.A. Oxon. Communicated by
W. Francois, Ph.D., F.L.S.

[Read Dec. 18, 1862.]

Tue distribution of the vascular tissues in the stem and stipes of
the British species of Ferns has been made the subject of much in-
teresting and accurate study by Dr. Ogilvie*. His papers are to
be found in the ‘Annals and Magazine of Natural History’ for
December 1859 and November 1860. My own long-continued
examination of the living plants has not enabled me to detect any
but the most trivial mistakes in these full and admirable memoirs.
I have therefore only to propose a few slight alterations in Dr.
Ogilvie’s conclusions, and to make one or two additional remarks
on certain species and varieties which he omits to notice. The
present communication may be deemed the first instalment of
such supplementary observations. I may also here state that I

* The following list of papers includes nearly all those in which the vascular
tissues of Ferns have been discussed :—

Presl. Tentamen Pteridographie. Prage: 1836.

Fée. Die Gefiissbiindel im Stipes der Farne. Prage: 1847.

Ogilvie, Dr. Ann. & Mag. Nat. Hist. 1859 and 1860.

Duval-Jouve, J. Etudes sur le Pétiole des Fougères, In Billot’s Archives
de la Flore de France; pp. 57 & 149.

King. On Sigillaria, Edinburgh Phil. Trans. 1844.

Leighton, Rey. W. A. Hints on a new character in Ferns. Phyt. n. s.i.
p. 256.

Moore, T. The Vascular Bundles of the Stipes of Ferns. Phyt. n. s.i. p. 378.

Reichardt, H. W. Ueber der Gefissbiindel Vertheilung im Stamme und
Stipes der Farne. Denkschriften der Kaiserlichen Akademie der Wissen-
schaften, xviite Band. Wien: 1859.

84 MR. CHURCH ON THE FORM OF THE

can confirm the general accuracy of Duval-Jouye’s figures so far
as they relate to species found in Britain.

To discuss the difficult question of the nomenclature of these
plants is beside my purpose; I shall therefore do no more than
designate each form named by two or three of its best-known
synonyms. At the same time, it seems that the results of such
inquiries as the present, as possibly affording criteria of generic if
not of specific difference, cannot be wholly ‘disregarded, and may
ultimately aid us in arriving at a more consistent classification
for the Filices.

The genera Polystichum and Lastrea as understood by Moore
and many other authors are respectively coextensive (so far as
our native ferns are concerned) with the genera Aspidiwm and

Nephrodium adopted by Hooker in his ‘ British Ferns’ (1862).

I have examined transverse sections of the stipes of all the gene-
rally received species and many of the varieties included under
these generic appellations, and in two species only did I find any
material departure from that one particular arrangement of the
vascular fasciculi which is disclosed by a transverse stipital section
of such a form as Moore's Lastrea Filix-mas or Polystichum Lon-
chitis. In Nephrodium Filix-mas, N. rigidum, N. cristatum, N.
spinulosum a. bipinnatum, 8. dilatatum, y. emulum, ò. dumetorum,
Aspidium aculeatum a. lobatum, B. intermedium, y. angulare of
Hooker, and also in the forms Lophodium glandulosum, L. uligi-
nosum, L. nanum, and L. collinum of Newman, the same disposi-
tion of the vascular tissue occurs. The two notable exceptions to
which I have before alluded are found in Nephrodium Thelypteris
and N. Oreopteris of Hooker, identical with the Lastrea Thely-
pteris and L. montana of Moore and the Hemestheum Thelypteris
and Lastrea (Hemestheum) montana of Newman. In fig. 1 the
prevalent arrangement is shown; in fig. 2 that which occurs in
the mountain fern; while fig. 3 represents that of the marsh fern,
which I will now more particularly describe. In all cases the
sections noticed are those of the stipes, not of the stem; and I
have freely availed my self of the use of a very weak solution of
perchloride of iron, in order that the tracts containing tannin
might be distinctly marked out.

Nephrodiwm Thelypteris, Hooker.
Hemestheum Thelypteris, Newman.
Lastrea Thelypteris, Moore.

The present plant is not only closely connected in many of its

E T

ON THE FERTILIZATION OF LYTHRUM SALICARIA. 169

integra, glabra, supra lucida; nervi laterales 12—15 utrinque costaque
utraque pagina prominuli; petiolus usque pollicem fere longus, teres,
glaber. Amenta axillaria, geminata, rarius abortu solitaria, breviter
(4 poll.) pedunculata, subtus nuda, supra floribus masculis densissime
obducta, foemineis paucis multo majoribus intermixtis. Bracteolæ
trigono-peltatæ, minutæ, pilosulæ, ciliolatæ, virides. Flores sessiles,
compacti, viridiusculi, dein albescentes. Sepala florum masce. basi in
tubum brevem connata, extus pilosula, ea flor. fæm. libera, exteriora
pubera, dein hirtella, interiora lævia, teneriora. Achænium pisi majoris
magnitudine, stylo persistente auctum, perigonio hirtello inclusum,
matnrescens contactu etiam levi elastice (ad 6 metr.) exsiliens.

In sylvis Sumatræ; in prov. Palembang; in prov. Padang prope Lumut et
ad littora prope Siboga, Teijsmann. Ins. Singapora, T. Anderson, M.D.

Nom. vernac. Kapinie.

Synon. Artocarpus elongatus, Mig. Fl. Ind, Bat. Suppl. p. 172 et 419.

Tas. XIII. fig. 1. Ramus floriferus magnit. nat.; fig. 2. Flos & et ?
auct. ut fig. sequent.; fig. 3. Sepalum exter. fl. 9 a dorso; fig. 4,
Sepal. inter. fl. 9 ; fig. 5. Ovarium ; fig. 6. idem, verticaliter transsect. ;
fig. 7. Semen, tegmento remoto. 7

On the Sexual Relations of the Three Forms of Lythrum salicaria.
By Cuartes Darwin, F.R.S., F.LS., &e.
[Read June 16, 1864.]
Some of the species of Lythrum offer in their manner of ferti-
lization a more remarkable case than can, perhaps, be found in
any other plant or animal. In Lythrum salicaria three plainly
different forms occur: each of these is an hermaphrodite, each
is distinct in its female organs from the other two forms, and
each is furnished with two sets of stamens or males differing
from each other in appearance and function. Altogether there
are three females and three sets of males, all as distinet from
each other as if they belonged to different species ; and if smaller
functional differences are considered, there are five distinct sets
of males. Two of the three hermaphrodites must coexist, and the
pollen be carried by insects reciprocally from one to the other,
in order that either of the two should be fully fertile; but unless
all three forms coexist, there will be waste of two sets of stamens,
and the organization of the species, as a whole, will be imperfect.
On the other hand, when all three hermaphrodites coexist, and
the pollen is carried from one to the other, the scheme is perfect ;
there is no waste of pollen and no false co-adaptation. In short,
nature has ordained a most complex marriage-arrangement,
namely a triple union between three hermaprodites,—each her-

$

7 Lian. 20e

PDT > in
Mo. Bot. Garden,

170 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

maphrodite being in its female organ quite distinct from the
other two hermaphrodites and partially distinct in its male
organs, and each furnished with two sets of males.

The three forms may be conveniently called, from the unequal
lengths of their pistils, the long-styled, mid-styled, and short-styled.
Their existence and differences were first observed by Vaucher*,
and subsequently more carefully by Wirtgen; but, not being guided
by any theory, neither author perceived some of the most curious
points of difference. I will first briefly describe the three forms
by the aid of the accompanying accurate diagram, which shows
the flowers, six times magnified, in their natural position, with
their petals and the near side of the calyx removed.

Long-styled form.—This can at once be recognized by the
length of the pistil, which is (including the ovarium) fully one-
third longer than that of the mid-styled, and more than thrice
as long as that of the short-styled form. It is so dispropor-
tionately long, compared with the flower, that it projects in
the bud through the unfolded petals. It stands out consi-
derably beyond the longer stamens; its terminal portion de-
pends a little, but the stigma itself is slightly upturned: the
globular stigma is considerably larger than that of the other
two forms. The six longer stamens project about two-thirds
of the length of the pistil, and correspond in length with the
pistil of the mid-styled form. The correspondence with the
pistil in length in this and the two following cases is generally
very close ; the difference, where there is any, being usually in a
slight excess of length in the stamens. The six shorter stamens
(each of which alternates with a longer one) lie concealed within
the calyx; their ends are upturned, and they are graduated in
length, so as to form a triple row—both which characters are
here much more marked than with the longer stamens, which
vary in these respects. The anthers of the shorter stamens are
smaller than those of the longer stamens. Knowing that the
pollen differs greatly in the longer and shorter stamens of the two
other forms, I carefully compared that of the two sets of stamens
in this form: in both the pollen-grains are yellow, but they are a
little larger in the longer than in the shorter stamens. The dit-
ference is slight, so that I convinced myself of its reality only by
putting two small heaps close together under the compound mi-

* Hist. Phys. des Plantes d'Europe, tom. ii., 1841, p. 371. Wirtgen, “ Ueber

Lythrum salicaria und dessen.Formen,” Verhand. des naturhist. Vereins der
preuss. Rheinl., 5. Jahrgang, 1848, S. 7.

THE THREE FORMS OF LYTHRUM SALICARIA. 174

Long-
styled.

Mid-
styled.

Short- Zi
styled. < .

Diagrams of the flowers of the three forms of Lythrum salicaria, in their
natural position, with the petals removed and with the near side of the clayx
cut away : enlarged six times.

The dotted lines with the arrows show which pollen must be applied to each
stigma to cause full fertility.

172 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

croscope, and I found I could always (with one exception) distin-
guish them: I then showed the specimens to two other persons,
and they likewise distinguished the two kinds and pointed out
which was the largest. The capsules of this form contain, on an
average, 93 seeds: how this average was obtained will presently
be explained. I repeatedly observed that the seed, when cleaned,
seemed larger than that from the mid-styled or short-styled
forms; consequently I placed 100 long-styled seeds in a good
balance, and by the double method of weighing found that they
equalled 121 seeds of the mid-styled and 142 of the short-styled ;
or, in short, that five long-styled seeds equalled six mid-styled and
seven short-styled seeds. These slight differences in the weight of
the seed, and, as we shall soon see, in the average number produced,
are worth recording, as they characterize not mere varieties but
coexisting forms of the same species.

Mid-styled form.—The pistil occupies the position represented
in the diagram, with its extremity considerably, but in a variable
degree, upturned ; the stigma is seated between the anthers of
the long and the short stamens. The six longer stamens correspond
in length with the pistil of the long-styled form ; their filaments
are coloured bright pink; the anthers are dark-coloured, but
from containing bright green pollen and from their early de-
hiscence they appear emerald-green. Hence the general appear-
ance of these stamens is remarkably dissimilar from that of the
longer stamens of the long-styled form. The six shorter stamens,
enclosed within the calyx, resemble in all respects the shorter
stamens of the long-styled form, and both correspond in length
with the short pistil of the short-styled form. The green pollen-
grains of the longer stamens are plainly larger than the yellow
pollen-grains of the shorter anthers: this fact was conspicuous in
several camera-lucida drawings made for me by my son, Mr. W. E.
Darwin. There is some variability in size, but 712, of an inch
may be taken as about the average diameter of the green pollen-
grains when distended with water, and 77 as the diameter of
the yellow grains of the shorter stamens ; so that the difference
in diameter is in about the proportion of four to three. The cap-
sules contain, on an average, 132 seeds ; but, perhaps, as we shall
see, this is rather too high an average. The seeds themselves are
smaller than those of the long-styled form.

Short-styled form.—The pistil is here very short, not one-third
of the length of that of the long-styled form. Tt is enclosed
within the calyx, which, differently from in the other two forms,

THE THREE FORMS OF LYTHRUM SALICARIA. 173

does not enclose any anthers. The end of the pistil is generally
bent upwards at right angles. The six longer stamens, with their
pink filaments and green pollen, resemble in size of the grains
and in all respects the longer stamens of the mid-styled form, and
both correspond in length with the long-styled pistil. The six
shorter stamens, with their uncoloured filaments and yellow pollen,
resemble in size of the grains and in all respects the longer
stamens of the long-styled form, and both correspond in length
with the mid-styled pistil. The capsules contain fewer seeds on
an average than in either of the preceding forms, namely 83-5, and
they are considerably smaller in size. In this latter respect, but
not in number, there is a gradation parallel to that of the length
of the pistil, the long-styled having the largest, the mid-styled the
` next in size, and the short-styled the smallest seed.

From this description we see that there are three distinct
female organs, or rather females as they are borne on distinct indi-
viduals, differing in the length and curvature of the style, in the
size of the stigma, and in the number and size of the seed. In the
three forms, taken together, there are thirty-six stamens or males,
and these can be divided into three sets of a dozen each, differing
from each other in length, curvature, and colour of the filaments,
in the size of the anthers, and especially in the colour and
diameter of the pollen-grains. Each of the three forms bears
half-a-dozen of one kind of stamens and half-a-dozen of another
kind, but not all three kinds. The three kinds correspond in
length with the three pistils: the correspondence is always be-
tween half the stamens borne by two forms with the pistil of a
third form. These remarks apply to the structure, and not, as yet,
to the functions, of the reproductive organs.

I ascertained the average number of seed by counting them in
eight fine selected capsules taken from plants of the three forms
growing wild, and the result was, as we have seen, for the long-
styled (neglecting decimals) 93, mid-styled 132, and short-styled
83. I should not have trusted this result, but I had a number
of plants in my garden which, from their youth, did not yield the
full complement of seed, but they were of exactly the same age
and grew under exactly the same conditions, and were freely
visited by bees. I took six fine capsules from each, and found
the average to be for the long-styled 80, for the mid-styled 97,
and for the short-styled 61. Lastly, I made numerous artificial
unions, and, as may be seen in the following Tables, these gave
in the long-styled an average of 90 seeds, in the mid-styled 117,

174 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

and in the short-styled 71. So that we have good concurrent
evidence of the different average production of seed by the three
forms. To show that the artificial fertilizations, presently to be
described, produced their full effect and may be trusted, I may
state that one mid-styled capsule yielded 151 good seeds, which
is the exact number of the finest wild capsule examined by me.
Artificially fertilized short- and long-styled capsules actually pro-
duced a greater number of seeds than I have found in wild plants,
but then I did not examine many of the latter. This Lythrum,
I may add, offers a remarkable instance, how profoundly ignorant
we are of the life-conditions of each species: naturally it grows
“in wet ditches, watery places, and especially on the banks of
streams,” and though it produces so many minute seeds, it never
spreads on the adjoining land; yet, planted in my garden, on
_ clayey soil lying over the chalk, and which is so dry that a rush
cannot be found, it thrives luxuriantly, grows to above six feet in
height, produces self-sown seedlings, and (which is a severer test)
is fully as fertile as in a state of nature. Nevertheless it would
be almost a miracle to find this plant spontaneously growing on
such land as my garden, though under its native climate.
According to Vaucher and Wirtgen, the three forms coexist in
all parts of Europe. Some friends gathered for me in North
Wales a number of twigs from separate plants growing near each
other, and then classified them. My son did the same in Hamp-
shire, and here is the result :—

| Long-styled. | Mid-styled. | Short-styled. | Total.
| | |
North Wales | 95 | 97 | 72 | 264
Hampshire. | 53 | 38 | 38 | 129
Ta RR ee m aa

If twice or thrice the number had been collected, probably the
three forms would have been found nearly equal; I infer this
from considering the above figures, and from my son telling me
that if he had collected in another spot, he felt sure that the
mid-styled plants would have been in excess. I several times
sowed small parcels of seed, and raised all three forms; but I
neglected to record the parent form, except in one instance, in
which I raised from short-styled seed twelve plants, of which only

one turned out long-styled, four mid-styled, and seven short-
styled.

THE THREE FORMS OF LYTHRUM SALICARIA. 175

Insects are necessary for the fertilization of this Lythrum.
During two years I kept two plants of each form protected, and
in the autumn they presented a remarkable contrast in appear-
ance with the adjoining uncovered plants, which were densely
covered with capsules. In 1863 a protected long-styled plant pro-
duced only five poor capsules ; two mid-styled plants produced the
same number ; and two short-styled plants between them produced
only one: these capsules contained very few seed; yet the plants
were fully productive when artificially fertilized under the net.
In a state of nature the flowers are incessantly visited for their
nectar by hive- and humble-bees and various Diptera. The nectar
is secreted all round the base of the ovarium; but a passage is
formed along the upper and inner side of the calyx by the lateral
deflection (not represented in the diagram) of the basal portions
of the filaments; so that insects invariably alight on the upper
side of the flowers, on the projecting stamens and pistil, and insert
their probosces along the upper inner margin of the calyx. We
can now see why the ends of the stamens with their anthers, and
the ends of the pistils with their stigma, are a little upturned, in
order that they may brush against the lower hairy surfaces of the
insects’ bodies. The short stamens which lie enclosed within the
calyx of the long- and mid-styled forms can be touched only by
the proboscis and the narrow chin of the sucking bee; hence they
have their ends more upturned, and they are graduated in length,
so as to fall into a narrow file, three deep, sure to be raked by
the thin intruding proboscis. The anthers of the longer stamens
stand laterally further apart and are more nearly of the same
length, for they have to brush against the whole breadth of the
insect’s body. I may here incidentally remark, that in very
many flowers the pistil, or the stamens, or both, are rectangularly
bent to one side of the flower: this bending may be permanent,
as with Lythrum and many others, or may be effected (as in
Dictamnus fraxinella and many others) by a temporary move-
ment which occurs in the stamens when the anthers dehisce,
and in the pistil when the stigma is mature; but these two
movements are by no means always contemporaneous in the
same flower. Now I have found no exception to the rule, that
when the stamens and pistil are bent, the bending is exactly to
that side of the flower which secretes nectar (even though there
be a rudimentary nectary of large size on the opposite side, as in

some species of Corydalis) ; or, when nectar is secreted on all

LINN, PROC,— BOTANY, VOR. VIII, P

176 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

sides, to that side where the structure of the flowers allows the
easiest access to it, as in Lythrum, Papilionaceous flowers, and
many others. The rule consequently is that when the pistil and
stamens are bent, the stigma and anthers are brought into the
pathway towards the nectary. There are a few cases which seem
to be exceptions, but they are not so in truth: for instance, in the
Gloriosa lily, the stigma of the grotesque and rectangularly bent
pistil is brought, not into the pathway from the open air towards
the nectar-secreting recesses of the flower, but into the circular
route from one nectary to the other; in Scrophularia aquatica
the pistil is bent downwards from the mouth of the flower, but
it thus strikes the pollen-dusted breasts of the wasps which
habitually visit these ill-scented blooms. In the above rule we see
one more instance of the supreme dominating power of insects
over all the minor structural details of flowers, especially of those
which have irregular corollas. Flowers which are fertilized by
the wind must of course be excepted, but I do not know of a
single instance of an irregular flower which is fertilized or crossed
by this means.

Ihave delayed too long on these points, but I must allude to
one other. We have seen that the three pistils of different
lengths have each two half-dozen sets of stamens of correspond-
ing length. When bees suck the flowers, the longest stamens,
bearing the green pollen, rub against the abdomen and the inte-
rior sides of the posterior legs, as does likewise the stigma of the
long-styled form. The stamens of middle length and the stigma
of the mid-styled form rub against the under side of the thorax
and between the front pair of legs. The shortest stamens and
the stigma of the short-styled form must rub against the pro-
boscis and chin; for the bees in sucking insert only the front of
their heads into the calyx. On catching bees, I observed much
green pollen on the inner sides of the hind legs and on the abdo-
men, and much yellow pollen on the under side of the thorax.
There was also pollen on the chin, and, it may be presumed, on
the proboscis, but this was difficult to observe. I had, however,
independent proof that pollen is carried on the proboscis; for in
a protected short-styled plant (which produced only two cap-
sules) one small branch was accidentally left durmg many days
pressing against the fine net, and bees were seen inserting their
probosces through the meshes, and in consequence numerous
capsules were formed on this one small branch. From these
several facts it follows that insects would chiefly carry to the

SIDERNE]

THE THREE FORMS OF LYTHRUM SALICARIA. 177

stigma of each form pollen from the stamens of corresponding
length ; and we shall presently see the importance of this adapta-
tion. It must not, however, be supposed that the bees do not
get more or less dusted all over with the several kinds of pollen;
they certainly do, as could be seen with the green pollen from
the longest stamens. Moreover, a case will presently be given of
a long-styled plant which grew absolutely by itself, and produced
an abundance of capsules, which must have been fertilized by its
own two kinds of pollen; but these capsules contained a very
poor average of seed. Hence insects, and chiefly bees, act both
as general carriers of pollen, and as special carriers of the right
kind *.

Variability—Before passing on to more important topics, I
must say a few words on this head. Wirtgen remarks t on the
variability in the branching of the stem,.in the length of the
bractez, size of the petals, and in several other respects. The
plants now growing in my garden have their leaves arranged op-
positely, alternately, and in whorls of three, and differ greatly in
shape. The stems of the plants bearing leaves in whorls are
hexagonal ; those of the other plants are quadrangular. But we
are concerned only with the reproductive organs: the upward
bending of the pistil is variable, and in a remarkable degree jn
the short-styled form, in which it is sometimes straight, some-
times slightly curved, but generally upturned at right angles.
The stigma of the long-styled pistil frequently has longer papillw
or is rougher than that of the mid-styled, and this than that of
the short-styled form ; but this character, though fixed and uni-
form with the two forms of Primula, is here variable, and I have

* In my paper on the two forms of Primula (Journal Proc. Linn. Soc. 1862,
p. 85) I stated that I had only occasionally seen humble-bes sucking the flowers
of the Cowslip (P. veris). Since then I have had some beds in my garden
containing nearly 700 plants, and these were incessantly visited by Bombus
hortorum and B. muscorum. I caught some of these bees, and I found (as I
had anticipated in my paper, p. 86) that a vast majority of the pollen-grains
which adhered to the base of the proboscis were large-sized and had come from
the long stamens of the short-styled form, and were thus placed ready to ferti-
lize the stigma of the long-styled form. On the other hand, on the middle, and
near the tip of the proboscis, a very large proportion of the pollen-grains were
of the small size, and had come from the short stamens of the long-styled form.
My son caught, also, a moth (Cucullia verbasci) hovering over the bed, and I
found on its proboscis a similar distribution of the two kinds of pollen-grains.
I give these facts as a further illustration of the importance of the relative
lengths of the stamens and pistil.

+ Verband. des naturhist. Vereins, 5. Jahrgang, 1848, 8. 11, 13,
P2

178 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

seen mid-styled stigmas rougher than those of the long-styled.
The degree to which the longer and middle stamens are graduated
in length and are upturned at their ends is variable; sometimes
all are equal. The colour of the green pollen in the long stamens
is variable +, and is sometimes pale greenish yellow ; in one short-
styled plant it was almost white. The grains vary a little in
size: I examined one short-styled plant with the grains above
the average size; and I have seen a long-styled plant with un-
distinguishable grains from the longer and shorter anthers. We
have here considerable fluctuations of character; and if any of
these slight structural differences were of direct service to the
plant, or were correlated with useful functional differences, we
can perceive that the species is just in that state in which natural
selection might readily do much for its modification.

To return to our proper subject—we see that there are three
kinds of females and three kinds of males, each kind of the latter
being borne by half-dozens on two of the three forms. It remains
to discover whether these several sexes or sexual organs differ from
each other in function. Nothing brings more prominently forward
the complexity of the reproductive system of this extraordinary
plant, than the necessity, in order to ascertain the above fact, of
artificially making eighteen distinct unions. Thus the long-styled
form had to be fertilized with pollen from its own two distinct
kinds of anthers, from the two in the mid-styled, and from the two
in the short-styled form. The same process had to be repeated
with both the mid- and short-styled forms. It might have been
thought sufficient to have tried on each stigma the green pollen,
for instance, from either the mid- or short-styled longer stamens,
and not from both; but the result proves that this would have-
been insufficient, and that it was necessary to try all six kinds of
pollen on each stigma. As in artificial fertilizations there will
always be some failures, it would have been advisable to have

* Lagerstremia Indica, one of the Lythracee, is strangely variable in its
stamens—I presume in part due to its growth in a hothouse. The most per-
fect flowers produced with me five very long stamens with thick flesh-coloured
filaments and green pollen, and from nineteen to twenty-nine short stamens with
yellow pollen; but many flowers produced only one, two, three, or four long
stamens with green pollen, which in some of the anthers was wholly replaced
by yellow pollen; one anther offered the singular case of half, or one cell being
filled with bright green, and the other cell with bright yellow pollen. One petal
had a furrow near its base, which contained pollen. According to analogy with
Lythrum, this species would produce three forms ; if so, the above plant was a
mid-styled form; it was quite sterile with its own two kinds of pollen.

THE THREE FORMS OF LYTHRUM SALICARIA. 179

repeated each of the eighteen unions a score of times; but the
labour would have been too great; as it was, I made 223 artificial
unions; 7. e., I fertilized, on an average, above a dozen flowers in
the eighteen different methods. Each flower was castrated ; the
adjoining buds had to be removed, that the marking-thread, wool,
&e. might be safely secured; and after each fertilization the
stigma had to be examined with a lens to see that there was suf-
ficient pollen. Plants of all three forms were protected during
two years by large nets on a framework ; two plants were used
during one or both years, in order to avoid any individual pecu-
liarity in any one plant. As soon as the flowers withered, the
nets were removed; and in the autumn the capsules were daily
inspected ; when the seeds were ripe they were counted under
the microscope. I have given these details that confidence may
be placed in the following Tables, and as some excuse for two
blunders which, I believe, I made. These blunders are referred
to, with their probable causes, in two notes to the Tables; the
erroneous numbers, however, are entered in the Tables, that it
may not be supposed that I have in any one instance tampered
with the results.

A few words explanatory of the three Tables must be given.
Each is devoted to one form, and is divided into six compartments.
The two upper ones in each table give the product of good seed
from the application of pollen from the two sets of stamens which
correspond in length with the pistil of that form. The two next
lower compartments show the result of pollen from the other two
sets of stamens, which do not correspond in length with the pistil,
and which are borne by the same two forms. The two lowest
compartments show the result of the application of each form’s
own two kinds of pollen. The term “own pollen,” used here and
in the Tables, does not mean pollen from the flower to be fertilized
—for this was never used—but from another flower on the same
plant, or more commonly from a distinct plant of the same form.
In the result given, “0” generally means that no capsule was
produced, or that the capsule contained no good seed. In some
part of each row of figures in each compartment, a short hori-
zontal line may be seen; the unions above this line were made in
1862, and below it in 1863. It is of importance to observe this,
as it shows that the same general result ensued in two successive
years; but more especially because 1863 was a very hot and dry
season, and the plants had occasionally to be watered. This did
not prevent the full complement of seed being produced from

180 MR. ©. DARWIN ON THE SEXUAL RELATIONS OF

the more fertile ‘unions ; but it rendered the less fertile unions
even more sterile than they otherwise would have been. I have
seen striking instances of this same fact in making homomorphic
and heteromorphie unions in Primula”; and it is well known
that the conditions of life must be highly favourable to give any
chance of producing hybrids from species which cross with diffi-
culty.

Table I.—Lone-styLtep Form.

|

| L
13 flowers fertilized by the longer
stamens of the mid-styled. These

stamens equal in length the pistil of
the long-styled.

I

13 flowers fertilized by the longer
stamens of the short-styled. These
stamens equal in length the pistil of
the long-styled.

Product of good seed in each capsule. | Product of good seed in each capsule.
36 159 104

53

81 0 43 119

0 0 96 poor seed. 96

0 0 103 99

0 0 Q 131

| — 0 0 116
| 45 wer
| 41 114

38 per cent. of these flowers yield-
“ed capsules. Each capsule contain-
ed, on an average, 51:2 seed.

84 per cent. of these flowers yield-
ed capsules. Each capsule con-
tained, on an average, 107‘3 seed.

* In the spring of 1862 I crossed forty Cowslip flowers (P. veris) hetero-
morphically and homomorphically. The plants were accidentally exposed in
the greenhouse to too hot a sun, and a number of umbels perished. Some,
however, remained in moderately good health, and on these there were twelve
flowers which had been fertilized heteromorphically and eleven which had been
fertilized homomorphically. The twelve heteromorphic unions yielded seven fine
capsules, containing on an average 57°3 good seed. Now mark the difference:
the eleven homomorphie unions yielded only two capsules, of which one con-
tained 39 seeds, but so poor, that I do not suppose one would have germinated,
and the other only 17 fairly good seed. It would be superfluous to give any
more details on this experiment, or on some which I made at the same time on
P. Sinensis, after the appearance of Mr. John Scott’s admirable paper on the
various dimorphic species of Primula, in which he confirms my former results,
and adds many original and valuable observations. Dr. Hildebrand has also
(Botanische Zeitung, 1864, Jan: L, S. 3) confirmed my general results with respect
to P. Sinensis, and has corrected an error into which in some unaccountable
manner I fell, namely, that the pollen-grains from the long- and short-styled
forms were of the same size. Dr. Hildebrand has added a series of new and
important experiments, for he fertilized homomorphically a number of flowers
with pollen from the same form, and likewise from the same individual flower.
These latter he found were thus rendered rather more sterile. This experiment,
I believe, has never been systematically tried before.

THE THREE FORMS OF LYTHRUM SALICARIA. 181

Table I.—Lone-styLep Form (continued).

TIT. IV.

14 flowers fertilized by the short | 12 flowers fertilized by the shorter
stamens of the mid-styled. stamens of the short-styled.
3 0 20 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 = 0
— 0 0 0
0 0 0
0 Too sterile for any average.
Too sterile for any average.
V. VI
15 flowers fertilized by own longer | 15 flowers fertilized by own shorter
stamens, stamens. £
2 — 4 —
10 0 8 0
23 0 4 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
Too sterile for any average. ° Too sterile for any average.

I fertilized a considerable number of flowers with pollen, taken by a
camel’s-hair brush, from both the long and short stamens of their own (long-
styled) form; but I did not examine with a lens (as I did in the cases in
the Tables) whether sufficient pollen had been placed on the stigma: only
5 capsules were produced, and these yielded on an average 14°5 seed. In
1863 I tried a much better experiment: a long-styled plant was grown
by itself, miles away from any other plant, so that its stigmas could have
received only the two kinds of pollen proper to this form. The flowers
were incessantly visited by bees, so that the stigmas must have received
on the most favourable days, and at the most favourable hours, successive
applications of pollen: all who have crossed plants know that this highly
favours fertilization. This plant produced an abundant crop of capsules ;
I took by chance 20, and these (excluding one poor one) contained seed as

holon = 20 20 35 21 19
26 24 12 23 10

7 30 27 29 13

20 12 29 19 35

This gives an average of 21-5 seed per capsule; and as we know that this
form, when standing near plants of the other two forms and fertilized by
- insects, produces an average of 93-1 seed per capsule, we see that the
long-styled form fertilized by its own two pollens yields only between
one-fourth and one-fifth of the full number of seed. I have spoken as if
this plant had received both its own kinds of pollen, and this is, of course,
possible; but, from the enclosed position of the shorter stamens, it is
much more probable that the stigma received almost exclusively the pollen
from its own longer stamens.

182

MR. C. DARWIN ON THE SEXUAL RELATIONS OF

Table II.—Mi1D-styrenD FORM.

I.

12 flowers fertilized by the longer
stamens of the long-styled. These
stamens equal in length the pistil of
the mid-styled.

Product of good seed in each capsule.

138 122
149 50
147 151
109 119
133 138
144 0

92 per cent. of the flowers (pro-
bably 100 per cent.) yielded cap-
sules. Each apsule contained, on
an average, 127°3 seed.

It

12 flowers fertilized by the shorter
stamens of the short-styled. These
stamens equal in length the pistil of
the mid-styled.

Product of good seed in each capsule.

112 109
130 143
143 124
100 145
33 12
a 141
104

100 per cent. of the flowers yielded
capsules. Each capsule contained,
on an average, 108'0 seed; or, ex-
cluding capsules with less than 20
seed, the average is 116:7 seed.

Ut.
13 flowers fertilized by the short
stamens of the long-styled.
1

0 19

~ sseed small
S 85 | and poor.
44 0
44 0
45 0

54 per cent. of the flowers yielded
capsules. Each capsule contained,
on an average, 47-4 seed; or, ex-
cluding capsules with less than 20
seed, the average is 60-2 seed,

Iv.
15 flowers fertilized by the longer
stamens of the short-styled.
0 6

8
` 115 113
14 29
6 17
2 113
9 79
— 128
132 0

93 per cent. of the flowers yielded
capsules. Each capsule contained,
on an average, 69:5 seed; or, ex-
cluding capsules with less than 20
seed, the average is 102°8.

V

12 flowers fertilized by own longer
stamens.

92 0
9 0
63 0
— 0
136 ?* 0
0 0

Excluding the capsule with 18
seed, 25 per cent. of the flowers |
yielded capsules, and each capsule
contained, on an average, 54-6 seed ;
or, excluding capsules with less than

20 seed, the average is 77°5,

Vi,
12 flowers fertilized by own shorter
stamens.

coool ooo
oooooco

© per cent. of the flowers yielded
capsules,

* I have hardly any doubt that this result of 136 seed is due toa gross error.
The flowers to be fertilized by their own longer stamens were first marked by

THE THREE FORMS OF LYTHRUM SALICARIA. 183

I fertilized a considerable number of flowers with pollen, taken by a
camel's-hair brush, from both the long and short stamens of their own
(short-styled) form ; but I did not examine with a lens (as I did in the
cases in the Tables) whether sufficient pollen had been placed on the
stigma: only 5 capsules were produced, and these yielded, on an ay erage,
11-0 seed,

Table IIT.—Snort-styrep Form.

I. TI.
12 flowers fertilized by the shorter | 13 flowers fertilized by the shorter
stamens of the long-sty led. These" stamens of the mid-styled. These
stamens equal tn length the pistil of | stamens equal in leng ary the pistil of

the short-styled. the short-styled,

69 56 93 69

61 88 77 69

88 112 48 53

66 lll 43 9

0 62 0 0

0 100 0 0

0

479 cent. of the flowers yielded | 61 per cent. of the flowers yielded
capsules. Each capsule contained, | capsules. Each capsule contained,

on ok average, 81°3 seed. | on an average, 64/6 seed,
TIL. | IV.
10 flowers fertilized by the longer | 10 flowers fertilized by the longer
stamens of the long-styled. stamens of the mid-styled.
0 14 0 0
0 0 | 0 0
0 0 | 0 0
0 0 | 0 0
= 0 | oa 0
23 0
Too sterile for any average. Too sterile for any average.

‘white thread,” and those by the longer stamens of the long-styled form by
“ white silk ;” a flower fertilized in the latter manner would have yielded about
136 seed, and it may be observed that one such pod is missing, viz., at the bottom
of compartment 1. Therefore I have hardly any doubt that I fertilized a
flower marked with “ white thread,” as if it had been marked with “ white silk,”
With respect to the capsule which yielded 93 seed, in the same column with that
which yielded 136, I do not know what to think. I endeavoured to prevent
pollen dropping from an upper to any lower flower, and I tried to remember
to wipe the pincers carefully after each fertilization ; but in making eighteen
different crosses, sometimes on windy days, and pestered by bees and flies buzzing
about, some few errors could hardly be avoided. One day I had to keep a
third man by me all the time to prevent the bees visiting the uncovered plants,
for in afew seconds’ time they might have done irreparable mischief. It was
also extremely difficult to exclude minute Diptera from the net. In 1862 I
made the great mistake of placing a mid-styled and long-styled under the same
huge net : in 1863 I avoided this error.

184 — MR. C. DARWIN ON THE SEXUAL RELATIONS OF

Table IIL.—Sxort-sTYyLED Form (continued).

V. yI.

` 10 flowers fertilized by own longer | 10flowers fertilized by own shorter
stamens. stamens.

0 0 64?* 0

9 0 0 0

0 0 0 0

— 0 — 0
0 0 21 0
0 9
Too sterile for any average. Too sterile for any average.

I fertilized a number of flowers without particular care with their own
two pollens, but they did not produce a single capsule; the position of
the stigma within the calyx renders the fertilization without some care
difficult.

Summary of the three preceding Tables.

Long-styled form.—T wenty-six flowers fertilized by the stamens
of corresponding length, borne by the mid- and short-styled forms,
yielded 61:5 per cent. of capsules, which contained, on an average,
89°7 seed.

Twenty-six flowers fertilized by the other and shorter stamens
of the mid- and short-styled forms yielded only two very poor
capsules.

Thirty flowers fertilized by this form’s own two sets of stamens
yielded only eight very poor capsules; but flowers well fertilized
by bees by one or both of their own kinds of pollen produced
numerous capsules containing, on an average, 21°5 seed.

Short-styled form.—Twenty-five flowers fertilized by the stamens
of corresponding length, borne by the long- and mid-styled forms,
yielded 72 per cent. of capsules, which (excluding one capsule
with only nine seeds) contained, on an average, 70°8 seed.

Twenty flowers fertilized by the longer stamens of the long-
and mid-styled forms yielded only two very poor capsules.

Twenty flowers fertilized by both their own two sets of stamens
yielded only two poor (or perhaps three) capsules.

Mid-styled form.—Twenty -four flowers fertilized by the stamens
of corresponding length, borne by the long- and short-styled
forms, yielded 96 (probably 100) per cent. of capsules, which con-

* T suspect that, by mistake, I fertilized this flower with the pollen of the
shorter stamens of the long-styled form, and it would then have yielded about
64 seed. Flowers to be thus fertilized were marked with black silk; those with

the pollen of the shorter stamens of the short-styled with black thread ; and thus,
I suspect, the mistake arose.

THE THREE FORMS OF LYTHRUM SALICARIA, 185

tained (excluding one capsule with 12 seed), on an average, 117'2
seed.

Fifteen flowers fertilized by the longer stamens of the short-
styled form yielded 93 per cent. of capsules, which (excluding
four capsules with less than 20 seed) contained, on an average,
102°8 seed.

Thirteen flowers fertilized by the shorter stamens of the long-
styled form yielded 54 per cent. of capsules, which capsules (ex-
cluding one with 19 seed) contained, on an average, 60°2 seed.

Twelve flowers fertilized by own longer stamens yielded 25 per
cent. of capsules, which (excluding one with 9 seed) contained, on
an average, 77:5 seed.

Twelve flowers fertilized by own shorter stamens yielded not a
single capsule.

Considering the three Tables and this summary, we may safely
draw the following conclusions. First, that, as in structure so in
function, there are three females or female organs: this is mani-
fest; for when all three receive the very same pollen, they are
acted on most differently. So conversely with the thirty-six sta-
mens, we know that they consist of three separate sets of a dozen
each, differing in various respects; and in function the pollen of
these three sets when applied to one and the same stigma acts
most differently, as a glance at the Tables proves. But we shall
presently see that the action of the pollen of the whole dozen
longest and of the whole dozen shortest stamens is not identical.

Secondly, we see that only the longest stamens fully fertilize
the longest pistil, the middle stamens the middle pistil, and the
shortest stamens the shortest pistil. And now we can compre-
hend the meaning of the almost exact correspondence in length
between the pistil of each form and the two half-dozen sets of
stamens borne by the two other forms; for the stigma of each
form is thus rubbed against the same spot of the insect’s body,
which becomes most charged with the proper pollen. In all three
forms, the female organ is but feebly, or not at all, acted on by its
own two kinds of pollen. In my papers on the dimorphism of
Primula and Linum, I used the terms “heteromorphic” for the
fully fertile unions between the female element of the one form
and the male element of the other, and “ homomorphic” for the
less fertile or quite sterile unions between the female and male
elements of the same form. The principle involved in these terms
holds good with Lythrum, but is insufficient ; for though in each
of the three forms the fertile unions are all heteromorphic, the ap-

186 MR. ©. DARWIN ON THE SEXUAL RELATIONS OF

propriate pollen coming from the stamens of corresponding length
borne by the other two forms, and though the homomorphic unions
of the females with their own two sets of males are always more
or less sterile, there remain in each case two other sterile unions,
not included in these two terms. Hence it will be found con-
venient to designate the two unions of each female with the two
sets of stamens of corresponding length, which are fully fertile, as
legitimate unions, and the four other, more or less sterile, unions
of each female with the four other sets of stamens as illegitimate
unions. Consequently, of the eighteen possible unions between
the three forms, six are legitimate and twelve are illegitimate.

Another and curious conclusion cannot be considered as proved,
but is rendered highly probable, by the Tables. The unions of
the pistils and stamens of equal length are alone fully fertile.
Now with the several illegitimate unions it will be found that the
greater the inequality in length between the pistil and stamens,
the greater the sterility of the result. There is no exception to
this rule. Thus, with the long-styled form, its own shorter sta-
mens are far less equal in length to the pistil than its own longer
stamens; and the capsules fertilized by the pollen of the shorter
stamens yielded fewer seeds: the same comparative result follows
from the use of the pollen of the shorter stamens of the mid-styled
form, which are much shorter than the shorter stamens of the short-
styled (see diagram), and therefore less equal in length to the long-
styled pistil. We shall see exactly the same result if we look to
the four illegitimate unions under the mid- and short-styled forms.
Certainly the difference in sterility in these several cases is very
slight, but the sterility always increases with the increasing
inequality of length between the pistil and the stamens which are
used, Therefore I believe in the above rule; but a vast number
of artificial unions would be requisite to prove it. Ifthe rule be
true, we must look at it as an incidental and useless result of the
gradational changes through which this species has passed in
arriving at its present condition. On the other hand, the corre-
spondence in length between the pistil of each form and those
stamens which alone give full fertility is clearly of service to the
species, and is probably the result of direct adaptation.

Some of the illegitimate unions yielded, as may be seen in the
Tables, during neither year a single seed; but, judging from the
case of the long-styled plant, it is probable, if such unions could
be effected repeatedly under the most favourable conditions, some
few seeds would be produced. Anyhow, I can state that in all

THE THREE FORMS OF LYTHRUM SALICARIA. 187

the eighteen possible unions the pollen-tubes penetrated, after
eighteen hours, the stigma. I have reason to believe that the
offspring from the illegitimate unions present some singular
characteristics; but until my observations on this head are re-
peated, I must be silent. At first I thought that perhaps two
kinds of pollen placed together on the same stigma would give
more fertility than any one kind; but we have seen that this is
not the case with each form’s own two kinds of pollen; nor is it
probable in any case, as I occasionally got, by the use of single
kinds of pollen, fully as many seed as I have seen in a capsule
naturally fertilized. Moreover the proper pollen from a single
anther is more than sufficient to fully fertilize each stigma; hence,
in this as in so many other cases, at least twelve times as much
of each kind of pollen is produced as is necessary to ensure full
fertilization. From the dusted condition of the whole body of
those bees which I caught on these flowers, it is probable that
some pollen of all kinds is deposited on each stigma; but there
can hardly be a doubt that the pollen of the stamens of corre-
sponding length will be prepotent and will wholly obliterate any
effect from the other kinds of pollen, even if previously deposited
on the stigma. I infer this partly from the fact ascertained by
Gärtner that each species’ own pollen is so prepotent over that of
any other species, that if put on the stigma many hours subse-
quently, it will entirely obliterate the action of the foreign pollen.
But I draw the above inference especially from the following
experiment: I fertilized homomorphically or illegitimately some
long-styled Cowslip flowers (Primula veris) with their own pollen,
and exactly twenty-four hours subsequently I fertilized these
same stigmas heteromorphically or legitimately with pollen from
a short-styled dark-red Polyanthus. I must premise that I have
raised many seedlings from crossed Cowslips and Polyanthus, and
know their peculiar appearance ; and I further know, by the test
of the fertility of the mongrels inter se, and with both parent
forms, that the Polyanthus is a variety of the Cowslip, and not of
the Primrose (P. vulgaris) as some authors haye supposed. Now
from the long-styled Cowslip twice fertilized in the manner ex-
plained, I raised twenty-nine seedlings, and every one of them
had flowers coloured more or less red; so that the heteromorphic
Polyanthus-pollen wholly obliterated the influence of the homo-
morphie pure Cowslip-pollen, which had been placed on the
stigmas twenty-four hours previously, and not a single pure
Cowslip was produced.

188 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

The last conclusion which may be deduced from the Tables,
even from a glance at them, is that the mid-styled form differs
from both the others in its much higher capacity for fertilization,
Not only did the twenty-four flowers fertilized by the stamens of
corresponding lengths, all, or all but one, yield capsules rich in
seed; but of the other four illegitimate unions, that by the longer
stamens of the short-styled form was highly fertile, though less
than in the two legitimate unions, and that by the short stamens
of the long-styled form was fertile to a considerable degree; the
two unions with this form’s own pollen were sterile, but im dif-
ferent degrees. So that the mid-styled form, when fertilized by
the six kinds of pollen, evinces five different grades of fertility.
By comparing compartments 3 and 6 in Table II. we learn a re-
markable fact, namely, that though the pollen from the short
stamens of the long-styled and from this form’s own (mid-styled)
short stamens, used in these two unions, is identical in all respects,
yet that its action is widely different ; in the one case above half
the fertilized flowers yielded capsules containing a fair number of
seed; in the other case not one single capsule was produced. So,
again, the green, large-grained pollen from the long stamens of
the short-styled and from this form’s own (mid-styled) long sta-
mens is identical in all respects, but its action,as may be seen in
compartments 4 and 5, is widely different. In both these cases
the difference in action is so plain that it cannot be mistaken, but
it can be corroborated. If we look to Table IHI., to the legiti-
mate action of the short stamens of the long- and mid-styled
forms on the pistil of the short-styled form, we again see a similar
but slighter difference, the pollen of the short stamens of the
mid-styled form yielding a smaller average of seed during the
two years of 1862 and 1863 than that from the short stamens of
the long-styled form. Again, if we look to Table I., to the legi-
timate action of the green pollen of the two sets of long stamens,
we shall find exactly the same result, viz. that the pollen of the
long stamens of the mid-styled form yielded during both years
fewer seeds than that from the long stamens from the short-styled
form. Hence it is certain that the two kinds of pollen produced
by the mid-styled form are less potent than the similar pollens
produced by the corresponding stamens of the two other forms,

When we see that the capsules of the mid-styled form yield
a considerably larger average number of seed than those of
the other two forms,—when we see how surely the flowers are
fertilized in the legitimate unions, and how much more productive

THE THREE FORMS OF LYTHRUM SALICARIA. 189

the illegitimate unions åre than those of the other two forms, we
are led to consider the mid-styled form as eminently feminine in
its nature. And although it is impossible to consider as rudi-
mentary or aborted the two perfectly developed sets of stamens
of the mid-styled form which produce an abundance of perfectly
well-developed pollen, yet we can hardly avoid connecting, as
balanced, the higher efficiency of the female organ with the lesser
potency of the two mid-styled pollens.

Fimally, it is proved by the Tables that Lythrum salicaria
habitually produces or consists of three females different in
structure and widely different in function; that it produces or
consists of three sets of males-widely different in structure and
function; and that two of the three sets of males are subdivided
into subgroups of half a dozen each, differing in a marked manner
in potency, so that regularly five kinds of pollen are elaborated
by this one species of Lythrum.

Lythrum Grefferi.—I must now say a few words about some of
the other species of the genus. I have examined numerous dried
flowers of L. Grafferi, each from a separate plant, kindly sent
me from Kew. This species, like Z. salicaria, is trimorphic, and
the three forms apparently occur in about equal numbers. In
the long-styled form the pistil projects about one-third of the
length of the calyx beyond its mouth, and is therefore shorter
than in Z. salicaria; the globose and hirsute stigma is larger than
that of the other two forms; the longer stamens, which are
graduated in length, have their anthers standing just above and
just beneath the mouth of the calyx; the half-dozen shorter
stamens rise rather above the middle of the calyx. In the mid-
styled form the stigma projects just above the mouth of the
calyx, and stands almost on a level with the longer stamens of
the previous form; its own longer stamens project well above the
mouth of the calyx and stand a little above the level of the stigma
of the long-styled form; the shorter stamens correspond in all
respects with the shorter ones in the previous form. In the
short-styled form the stigma of the pistil is nearly on a level with
the anthers of the shorter stamens in the two preceding forms;
and the longer stamens correspond with the longer stamens of
the mid-styled form, and the shorter stamens with the longer
stamens of the long-styled form. In short, there is a close general
correspondence in structure between this species and L. salicaria,
but with some differences in the proportional lengths of the parts.
Nevertheless the fact of each of the three pistils having two sets

190 MR. ©. DARWIN ON THE SEXUAL RELATIONS OF

of stamens, borne by the two other forms, of corresponding lengths,
comes out conspicuously. In the mid-styled form the distended
pollen-grains from the longer stamens had nearly double the
diameter of those from the shorter stamens; so that there is a
greater difference in this respect than in L. salicaria. In the
long-styled form, also, the difference in diameter between the
pollen-grains of the longer and shorter stamens was plainer than
in L. salicaria. These comparisons, however, must be received
with caution, as they were made on specimens long kept in a
dried condition.

Lythrum thymifolia—This form, according to Vaucher*, is
dimorphic like Primula, and therefore presents only two forms.
I received two dried flowers from Kew, which presented two
forms: in the one form the stigma projected far beyond the calyx,
in the other it was included within the calyx; in this latter form
the style was only one-fourth of the length of the style of the
other form. There are only six stamens; these are somewhat
graduated in length, and in the short-styled form the anthers
stand a little above the stigma, but yet the stamens by no means
equal in length the pistil of the long-styled form; in the long-
styled form the stamens are rather shorter than in the other
form. These six stamens alternate with the petals, and corre-
spond homologically with the longer stamens of L. salicaria and
L. Grefferi. As there are only six stamens, it is scarcely possible
that this species can be trimorphie.

Lythrum hyssopifolia.—This species is said by Vaucher, but I
believe erroneously, to be dimorphic. I have examined dried
flowers from twenty-two separate plants from various localities,
kindly sent to me by Mr. Hewett C. Watson, Prof. Babington, and
others. These were all essentially alike. Hence the species cannot
be dimorphic. The pistil varies somewhat in length, but when un-
usually long the stamens are likewise generally long ; in the bud the
stamens are short: perhaps these circumstances deceived Vaucher.
There are from six to nine stamens, graduated in length; the sta-
mens which are variable in being present or absent correspond with
the six shorter stamens of L. salicaria and with the six which are
absent in L. thymifolia. The stigma is included within the calyx,
and stands in the midst of the anthers, and would generally be
fertilized by them; but as the stigma and anthers are upturned,
and as, according to Vaucher, there is a passage left in the upper
side of the flower to the nectary, there can hardly be a doubt that

* Hist. Phys, des Plantes d’Europe, tom, ii, (1841) pp. 369, 371.

THE THREE FORMS OF LYTHRUM SALICARIA, 191

the flowers are visited by insects, which would occasionally bring
pollen from other flowers of the same or of any adjoining plant,
as surely as occurs with the short-styled Z. salicaria, of which
the pistil and corresponding stamens closely resemble those of
L. hyssopifolia. According to Vaucher and Lecoq*, this species,
which is an annual, generally grows almost solitarily, whereas the
three preceding species are social; and this alone would almost
have convinced me that LZ. hyssopifolia cannot be dimorphic, as
such plants cannot habitually live by themselves any better than
one sex of a dicecious species.

Nesea verticillata.—I raised a number of plants from seed sent
me by Professor Asa Gray,and they presented three forms. These
differed from each other in the proportional lengths of their organs
of fructification and in all respects in very nearly the same way as
the three forms of Lythrum Grefferi. The green pollen-grains from
the longest stamens, measured along their greater axis and not
distended with water, were +12, of an inch in length; those from
the stamens of middle length 2544, and those trom the shortest
stamens 7°), of an inch.

We have seen that the genus Lythrum affords trimorphic, dimor-
phic, and monomorphic species.

The inquiry naturally arises, why do these species differ so
remarkably in their sexual relations? of what service can reci-
procal dimorphism or trimorphism be to certain species, whilst
other species of the same genus present, like the great majority of
plants, only one form? Ihave elsewhere given too briefly the

* Géograph. Bot. de Europe, tom. vi. (1857) p. 157.

+ ‘Origin of Species,’ 3rd edit., p. 101. Hugo yon Mohl has recently (Bot.
Zeitung, 1863, S. 309, 321), in a most interesting paper, advanced the case of the
minute, imperfectly developed, closed and self-fertile flowers borne by Viola,
Oxalis, Impatiens, Campanula, &c., as an argument against my doctrine that no
species is self-fertilized for perpetuity. I may state that in the spring of 1862 I
examined some of these flowers, and saw, though less thoroughly, all that
H. von Mohl has so well described. I can add only one remark, which I
believe is correct, that in V. canina there is an open channel for the pollen-
tubes from the extremity of the stigma to the ovarium ; for i gently pressed a
minute bubble of air repeatedly backwards and forwards from end to end.
Though the imperfectly developed and the perfect flowers are so different in
structure, it is a rather curious case of correlation, that in the double purple
Violet (F. odorata) the minute imperfect flowers are double to the very core,
so that a section appears like the head of a cabbage when cut through. There
can be, as von Mohl asserts, no doubt that these flowers are always self-fertilized ;
they are moreover specially adapted for this end, as may be seen in the remark-
able difference in the shape of the pistil in V. canina (and in a less degree in
V. hirta and the single V. odorata) as compared with that of the perfect flower ;

LINN. PROC.— BOTANY, VOL. VIII, Q

192 MR. C. DARWIN ON THE SEXUAL RELATIONS OF

general grounds of my belief that with all organic beings distinct in-
dividuals at least occasionally cross together, and reciprocal dimor-
phism is plainly one most efficient means for ensuring this result.

and in the pollen-tubes which proceed from the grains within the anthers in
V. canina, and from within the lower anthers of Oxalis acetosella, having the
wonderful power of directing their course to the stigma. If these plants had
produced the minute closed flowers alone, the proof would have been perfect
that they could never have crossed with other individuals. Iam aware that
in some of these cases it has been stated that the perfect flowers never produce
any seed; as far as Amphicarpea is concerned, I hear from Professor Asa Gray
that the petaliferous flowers certainly sometimes yield seed. The completely
enclosed flowers of that curious grass, the Leersia oryzoides, as described by M.
Duval-Jouve (Bull. Soc. Bot. de France, tom. x. 1863, p. 194), apparently offer
the best case of perpetual self-fertilization ; for when perfect flowers are pro-
truded from the culms, they are, as far as is yet known, always sterile. Ina
number of plants kept by me in pots in water, not one single perfect flower has
protruded, but the enclosed flowers produced plenty of seed. Without wishing
to throw any doubt on M. Duval-Jouve’s excellent observations, I may add that
with the enclosed flowers borne by my plants, the act of fertilization, that is,
the penetration of the stigma by the pollen-tubes, took place in the air and not
in fluid within the glumes. With the exception of the Leersia, as the case now
stands, I cannot see how the production of the small, imperfect flowers invali-
dates my doctrine that no species is perpetually self-fertilized, more than the
multiplication of many plants by bulbs, stolons, &e. As I observe that the pro-
duction of seed by the perfect flowers of Viola is spoken of as something capri-
cious and accidental, I may state that, although it varies much in different years,
it depends exclusively on the visits of bees; I ascertained this by marking many
flowers thus visited, and finding that they produced capsules, and by covering up
many flowers which (excepting a few that I artificially fertilized) did not, when
thus protected, produce a single capsule. After bees have visited these flowers, the
pollen may be seen scattered on the papilla and on the stigma itself, and they can
hardly fail thus to cross distinct individuals. These remarks apply to V. canina,
hirta, and odorata; with V. tricolor the case is somewhat different; but I
must not enlarge any more on this subject. The production by so many plants
of perfect and expanded, as well as of imperfect and closed flowers, seems to me
to throw much light on many points; it shows how extraordinarily little
pollen is necessary for full fertilization, for I ascertained with V. canina that the
perfect and imperfect flowers (the latter producing so few pollen-grains) yielded
the same average number of seeds ; it shows us that fertilization can be perfected
in closed flowers ; it shows us that large; highly coloured petals, perfume, and
the secretion of nectar are by no means indispensable for this act, even in those
species which properly possess these characters. It seems to me that the neces-
sity of an occasional cross with a distinct individual of the same species explains
the universal presence of at least some expanded flowers, at the expense of injury
from rain and the loss of much pollen by innumerable pollen-robbing insects ;
it explains the enormous superfluity of pollen from its liability to loss from these
eauses and during conveyance from flower to flower; it explains the use of a
gaily coloured corolla, perfume, and nectar, namely, to attract insects, except in
those comparatively few cases in which wind is the agent, and in these the last-
named attributes are deficient.

THE THREE FORMS OF LYTHRUM SALICARIA. 193

This result would appear to be one of high importance, for with
dimorphic plants it is ensured at the risk of occasional sterility ;
not only is the pollen of each plant useless or nearly useless to
that individual, but so is the pollen of all the plants of the same
form, that is, of half the total number of individual plants. In
that extensive class of plants called by C. K. Sprengel dicho-
gams, in which the pollen of each flower is shed before its own
stigma is ready, or in which the stigma (though this case occurs
more rarely) is mature before the flower’s own pollen is ready
sterility can hardly fail to be the occasional result; and it would
be the inevitable result with both dichogamous and reciprocally
dimorphic flowers unless pollen were carried by insects (and in
some few species by the wind) from one flower or plant to the
other. As with reciprocal dimorphism so with dichogamy,
. within the same genus some of the species are and some are not
thus characterized. Again, in the same genus, as in that of
Trifolium, some species absolutely require insect-aid to produce
seed, others are fertile without any such aid; now when insects are
requisite for fertilization, pollen will generally be carried from one
flower to the other. We thus see, by means of reciprocal dimor-
phism, of dichogamy, and of insect-aid, that some species require,
or at least receive, incessant crosses with other individuals of the
same species; whereas other species of the same genera can be,
and probably are often fertilized during long periods by the
pollen of their own flowers. Why this wide difference in the
frequency of crosses should occur we are profoundly ignorant. I
will only further remark on this head, that it would be a great
mistake to suppose that many flowers, which are neither reci-
procally dimorphic nor dichogamous, nor require insect-aid for
their fertilization, nor show any particular adaptation in their
structure for the visits of insects, are not habitually crossed with
the pollen of other individuals; this occurs, for instance, habitually
with cabbages, radishes, and onions, which nevertheless are per-
fectly fertile (as I know by trial) with their own pollen without
aid of any kind.

But it may be further asked, granting that reciprocal dimor-
phism is of service by ensuring at each generation a cross (but I
am far from pretending that it may not have some additional
unknown signification), why did not dimorphism suffice for
L. salicaria and Grefferi? why were they rendered reciprocally
trimorphic, entailing such complicated sexual relations? We
cannot answer, except perhaps so far :—if we suppose two plants of

Q2

194 MR. C. DARWIN ON TILE SEXUAL RELATIONS OF

the Z. salicaria to grow by themselves, then if the species were
dimorphic it would only be an equal chance in favour of the two
turning out different forms and consequently both being fertile ;
but as the species is trimorphie and each form can fertilize the
two other forms, it is two to one in favour of the two turning out
different forms and being consequently both fertile. We thus
see how reciprocal trimorphism must be an advantage; and
probably it would be more advantageous to this Lythrum, which
commonly grows in almost a single row along the banks of
streams, than it would be to Primroses or Cowslips which have
neighbours on all sides. But even if trimorphism effected ho
good beyond that gained by dimorphism, we ought not to feel
much surprised at its occurrence, for we continually see throughout
nature the same end gained by the most complicated as well as by
the most simple means: to give one instance :—in mahy dicecious
plants pollen is carried from the male to the female by the wind,
which is perhaps the simplest method conceivable, or by the
adherence of the grains to the hairy bodies of insects, which is a
method only a little less simple; but in Catasetum the conveyance
is effected by the most complex machinery ; for in this orchid we
have sensitive horns which when touched cause a membrane to
rupture, and this sets free certain springs by which the pollen-
masses are shot forth like an arrow, and they adhere to the
insect’s body by a peculiar viscid matter, and then by the breaking
of an elastic thread of the right strength the pollen is left sticking
to the stigma of the female plant. The complexity of the means
used in this and in many other cases, in fact depends on all the
previous stages through which the species has passed, and on the
successive adaptations of each part during each stage to changed
conditions of life.

As some authors consider reciprocal dimorphism to be the first
step towards dicciousness, the difficulty of understanding how a
trimorphic plant like Zythrum salicaria could become dicecious
should be noticed; and as dimorphism and trimorphism are so
closely allied, it is not probable that either state is necessarily
in any way related to a separation of the sexes—though it may
occasionally lead to this end. As far as Lythrum salicaria is con-
cerned, the one tendency which we can discover is towards the
abortion of the two sets of stamens in the mid-styled form. This
tendency is evinced by its pollen, though abundant and apparently
good, yielding a smaller percentage of seed than does the pollen
of the corresponding stamens in the other two forms; and this

THE THREE FORMS OF LYTHRUM SALICARIA. 195

fact is in itself curious, and shows by what insensibly graduated
steps nature moves. If this tendency were carricd out the
mid-styled form would become a female, depending for its fer-
tilization on two sets of stamens in the long- and short-styled
forms; and these two forms would reciprocally fertilize each other
like the two forms of Primula or Linum; but there would be no
approach to a dicecious condition.

As the case of the trimorphie species of Lythrum is so com-
plicated, and as it is easier to perceive the relations of the sexes
in the animal than in the vegetable kingdom, it may be worth
while to give, before concluding, a somewhat elaborate simile.
We may take the case of a species of Ant, and suppose all the
individuals invariably to live in three kinds of communities ; in
the first, a large-sized female (not to specify other differences)
living with six middle-sized and six small-sized males; in the
second, a middle-sized female with six large- and six small-sized
males; and in the third community, a small-sized female with six
large- and six middle-sized males. Each one of these three
females, though enabled to unite with any male, would be nearly
sterile with her own two sets of males, and likewise with two
other sets of males living in the other two communities; for she
would be fully fertile only when paired with a male of her own
size. Hence the thirty-six males, distributed by half-dozens in
the three communities, would be divided into three sets of a
dozen each; and these sets, as well as the three females, would
differ from each other sexually in exactly the same manner as
distinct species of the same genus. Moreover the two sets of
males living in the community of the extraordinarily fertile
middle-sized female would be less potent sexually than the males
of corresponding size in the two other communities. Lastly, we
should find that from the eggs laid by each of the three females,
all three sorts of females and all three sorts of males were
habitually reared—proving to demonstration that all belonged to
one and the same species.

To appreciate fully this remarkable case of the reciprocally tri-
morphic species of Lythrum, we may take a glance at the two great
kingdoms of nature and search for anything analogous. With
animals we have the most astonishing diversity of structure in
the so-called cases of alternate generation, but as such animals
have not arrived at maturity, they are not properly comparable
with the forms of Lythrum. With mature animals we have
extreme differences in structure in the two sexes; we have in

196 . MR. C. DARWIN ON LYTHRUM SALICARIA.

some of the lower animals males, females, and hermaphrodites
of the same species; we have the somewhat more curious case
of certain Cirripedes which are hermaphrodites, but are sexually
aided by whole clusters of what I have called complemental
males; we have, as Mr. Wallace has lately shown, the females of
certain Lepidoptera existing under three distinct forv s; but in
none of these cases is there any reason to suspect tit there
is more than one female or one male sexual element. With
certain insects, as with Ants, in which there exist, besides

males and females, two or three castes of workers, we have a

slightly nearer approach to our case, for the workers are so far
sexually affected as to have been rendered sterile. With plants,
at least with phanerogamic plants, we have not that wonderful
series of successive developmental forms so common with animals ;
nor could this be expected, as plants are fixed to one spot from
their birth, and must be adapted throughout life to the same
conditions. With plants we have sexual differences in structure,
but apparently less strongly marked than with animals, from
causes which are in part intelligible, such as there being no
sexual selection; again, we haye that class of dimorphic flowers

so ably discussed recently by Hugo yon Mohl, in which some -
of the flowers are minute, imperfectly developed, and neces- -

sarily self-fertile, whilst others are perfect and capable of
crossing with other flowers of the same species; but in these
several cases we have no reason to suspect that there is more
than one female or one male sexual element. When we come to
the class of reciprocally dimorphic plants, such as Primula, Linum,
&c., we first meet with two masculine and two feminine sexes.
But these cases, which seemed only a short time since so strange,
now sink almost into insignificance before that of the trimorphic
species of Lythrum.

Naturalists are so much accustomed to behold great diversities
of structure associated with the two sexes, that they feel no
surprise at the fact; but differences in sexual nature have been
thought to be the very touchstone of specific distinction. We
now see that such sexual differences—the greater or less power
of fertilizing and being fertilized—may characterize and keep
separate the coexisting individuals of the same species, in the
same manner as they characterize and have kept separate those
groups of individuals, produced from common parents during the
lapse of ages or in different regions, which we rank and deno-
minate as distinct species.

Nn tN

[From the ANNALS AND MAGAZINE OF NATURAL History For
September 1869.]

NOTES

ON

THE FERTILIZATION OF ORCHIDS.

BY
CHARLES DARWIN, M.A., F.R.S.
eres

To the Editors of the Annals and Magazine of Natural History.

GENTLEMEN,

Having drawn up some notes for a French translation of
my work ‘On the various contrivances by which British and
Foreign Orchids are Fertilized by Insects’ (1862), it has ap-
peared to me that these notes would be worth publishing in
English. I have thus been able to bring up the literature of
the subject to the present day, by giving references to, together
with very brief abstracts of, all the papers published since my
work appeared. These papers contain, on the one hand, cor-
rections of some serious errors into which I had fallen, and,
on the other hand, confirmations of many of my statements.
I have also been able to add, from my own observations and
those of others, a few new facts of interest. A heading is
given to each note, which will show the nature of the correc-
tion or addition, without any reference to my book ; but I have
added in a parenthesis the page to which the note ought to be
appended.

Gentlemen,
Down, Beckenham, Kent. Your obedient Servant,
July 23, 1869. CHARLES DARWIN.

yramidalis (p. 20).—The late Prof.

Orchis or Anacamptis ? 4
Treviranus has confirmed (Botanische Zeitung, 1863, p. 241)

my observations on this remarkable species ; but he differs from
me in one or two minor points. :
On the kinds of Insects which habitually visit and fertilize

some of the common British species of Orchis (p. 35).—I believe
A

2 Mr. C. Darwin on the Fertilization of Orchids.

that it may be safely predicated that orchids with very long
nectaries, such as the Anacamptis, Gymnadenia, and Platan-
thera, are habitually fertilized by Lepidoptera, whilst those
with only moderately long nectaries are fertilized by bees and
Diptera—in short, that the length of the nectary is correlated
with that of the proboscis of the insect which visits the plant.
I have now seen Orchis morio fertilized by various kinds of
bees, namely :—by the hive-bee (Apis mellifica), to some of
which from ten to sixteen pollen-masses were attached; by
Bombus muscorum, with several pollen-masses attached to the
bare surface close above the mandibles; by Eucera longi-
cornis, with eleven pollen-masses attached to its head; and
by Osmia rufa. These bees, and the other Hymenoptera
mentioned throughout these notes, have been named for me by
our highest authority, Mr. Frederick Smith, of the British
Museum. The Diptera have been named by Mr. F. Walker,
of the same establishment. In Northern Germany, Dr. H.
Miiller of Lippstadt found pollen-masses of Orchis morio at-
tached to Bombus silvarum, lapidarius, confusus, and pra-
torum. The same excellent observer found the pollen-masses
of Orchis latifolia attached to a Bombus; but this orchis is
also frequented by Diptera. A friend watched for me Orchis
mascula, and saw several flowers visited by a Bombus,
apparently B. muscorum; but it is surprising how seldom
any insect can be seen visiting this common species. With
respect to Orchis maculata, my son, Mr. George Darwin, has
clearly made out the manner of its fertilization. He saw many
specimens of a fly (Empis livida) inserting their proboscides into
the nectary; and subsequently I saw the same occurrence.
He brought home six specimens of this Empis, with pollinia
attached to their spherical eyes, on a level with the bases of
the antennee. The pollinia had undergone the movement of
depression, and stood a little above and parallel to the pro-
boscis: hence they were in a position excellently adapted to
strike the stigma. Six pollinia were thus attached to one spe-
cimen, and three to another. My son also saw another and
smaller species (Hmpis pennipes) inserting its proboscis into
the nectary ; but this species did not act so well or so regu-
larly as the other in fertilizing the flowers. One specimen of
this latter Empis had five pollinia, and a second had three
pollinia, attached to the dorsal surface of the convex thorax.
On nectar being secreted and contained between the outer
and inner membranes of the nectary in several species of Orchis
(p. 51).—I have repeated my observations on the nectaries of
some of our common species, and especially on those of Orchis
morto, at the time when various bees were continually visiting

Mr. C. Darwin on the Fertilization of Orchids. 3

the flowers; but I could never see the minutest drop of nectar
within the nectary. Each bee remained a considerable time
with its proboscis in constant movement whilst inserted into
the nectary. I observed the same fact with Empis in the case
ot Orchis maculata; and in this orchis I could occasionally
detect minute brown specks, where punctures had been made,
Hence the view suggested by me that insects puncture the
inner lining of the nectary and suck the fluid contained be-
tween the two coats may be safely accepted. I have said in
my work that this hypothesis was a bold one, as no instance
was known of Lepidoptera penetrating with their delicate pro-
boscides any membrane; but I now hear from Mr. R. Trimen
that at the Cape of Good Hope moths and butterflies do much
injury to peaches and plums by penetrating the skin, in parts
which have not been in the least broken.

Since the appearance of my work, the following observations
havebeen publishedon other species of Orchisand on certain allied
Jorms (p. 53).—Mr. J. Traherne Mogeridge has given (Journ.
Linn. Soc. vol. viii. Botany, 1865, p. 256) a very interesting
account of the structure and manner of fertilization of Orchis
or Aceras longibracteata. Both pollinia, as in Anacamptis
pyramidalis, are attached to the same viscid disk ; but, differ-
ently from those in that species, after being removed from the
anther-cases, they first converge and then undergo the move-
ment of depression. But the most interesting peculiarity in
this species is that insects suck nectar out of minute open cells
in the honeycombed surface of the labellum. Mr. Moggridge
saw this plant fertilized by a large bee, the Xylocopa violacea.
He adds some observations on Orchis hircina, and describes
the structure and manner of fertilization of Serapias cordigera
by another bee, viz. the Ceratina albilabris. In this Serapias
both pollinia are attached to the same viscid disk; when first
withdrawn, they are bent backwards, but soon afterwards
move forwards and downwards in the usual manner. As the
stigmatic cavity is narrow, the pollinia are guided into it by
two guiding plates. oe

Mr. Moggridge sent me from Northern Italy living plants
of Orchis or Neotinea intacta, together with excellent drawings
and a full account of the structure of the flower. He informed
me that this species is remarkable for producing seed with-
out the aid of insects; and I ascertained that when insects
were carefully excluded, almost all the flowers produced cap-
sules. Their fertilization follows from the pollen being ex-
tremely incoherent, and spontaneously falling on the stigma.

Nevertheless a short nectary is present, the moa possess
A D

4 Mr. C. Darwin on the Fertilization of Orchids.

small viscid disks, and all the parts are so arranged that, if
insects were to visit the flowers, the pollen-masses would pro-
bably be removed and then carried to another flower, but not
so effectually as with most other orchids. We shall hereafter
find a few other cases of orchids which have structural pecu-
liarities adapted both for self-fertilization and for crossing. I
may here also refer to a paper by Mr. R. Trimen (Journ. Linn.
Soc. vol. vii. Botany, 1863, p. 144) on the beautiful Disa
grandiflora of the Cape of Good Hope. This orchid presents
several remarkable characteristics, one of these being that the
pollinia do not spontaneously undergo any movement of de-
pression, the weight of the pollen-masses sufficing to bend the
caudicle into the proper curvature for the act of fertilization.
Another peculiarity is that the posterior sepal secretes nectar,
and is developed into a spur-like nectary. Mr. Trimen in-
forms me that he has seen a Dipterous insect, allied to Bom-
bylius, frequenting the flowers. I may add that Mr. Trimen
has sent me descriptions and specimens of various other South-
African orchids, which confirm the general conclusions at
which I have arrived in my work.

On the movement of the pollinia of Ophrys muscifera (p. 56).
—Mr. T. H. Farrer, who has lately been attending to the fer-
tilization of various plants, has convinced me that I have
erred, and that the pollinia of this Ophrys do undergo a move-
ment of depression. Hence my remarks on the correlation of
the various parts of the flower are to a certain extent invali-
dated; but there can be no doubt that the naturally bent
caudicle plays an important part in placing the pollen-mass
in a proper position for striking the stigma. I have continued
occasionally to watch the flowers of this species, but have
never succeeded in seeing insects visit them; but I have been
led to suspect that they puncture or gnaw the small lustrous
prominences beneath the viscid disks, which, I may add, are
likewise present in several allied species. I have observed
very minute punctures on these prominences, but I could not
decide whether these had been made by insects or whether
superficial cells had spontaneously burst.

Ophrys aranifera (p. 63).—F. Delpino states (Fecondazione
nelle Piante &c., Firenze, 1867, p. 19) that he has examined in
Italy thousands of specimens P this Ophrys, and that it sel-
dom produces capsules. It does not secrete any nectar. Al-
though he never saw an insect on the flowers (excepting once
a green locust), nevertheless they are fertilized by insects ; for
he found pollen on the stigmas of some flowers, which had their
own pollinia still within the anther-cases. The pollinia never

Mr. C. Darwin on the Fertilization of Orchids. 5

spontaneously fall out. He appears to think that I infer that
this Ophrys tertilizes itself, which is an error.

Ophrys apifera (p. 71).—Prof. Treviranus at first doubted
(Botanische Zeitung, 1862, p. 11) the accuracy of my account of
this Ophrys, and of the differences between it and O. arach-
nites; but he has subsequently (Bot. Zeit. 1863, p. 241) fully
confirmed all that I have stated.

Ophrys arachnites (p.72).—I have now examined several ad-
ditional living specimens of this Ophrys, and can confirm my
statement that the pollinia do not fall out of the anther-cases,
even when the spikes are strongly shaken; nor do they fall
out when the spikes are kept standing in water for a week.
Mr. J. Moggridge has made (Journ. Linn. Soc., Bot. vol. viii.
1865, p. 258) a remarkable observation on O. scolopax, which
is closely allied to O. arachnites,—namely, that at Mentone it
never exhibits any tendency to self-fertilization, whilst at
Cannes all the flowers fertilize themselves, owing to a slight
modification in the curvature of the anther, which causes the
pollinia to fall out. This botanist has given, in his " Flora of
Mentone,’ a full description, with excellent figures, of O. scolo-
pax, arachnites, aranifera, and apifera; and he believes, from
the number of intermediate forms, that they must all be
ranked as varieties of a single species, and that their differ-
ences are intimately connected with their period of flowering.
It does not appear that these forms in England, judging from
their distribution, are liable to pass into each other, within any
moderate or observable period of time.

On the fertilization of Herminium monorchis (p. 74).—My
son, Mr. George Darwin, has fully observed the manner of
fertilization of this minute and rare orchis. It differs from
that of any other genus known to me. He saw the flowers
entered by various minute insects, and brought home no less
than twenty-seven specimens with pollinia (generally with only
one, but sometimes with two) attached to them. These insects
consisted of minute Hymenoptera (of which Tetrastichus dia-
phantus was the commonest), of Diptera and Coleoptera, the
latter being Malthodes brevicollis. The one indispensable
point appears to be that the insect should be of very minute
size, the largest being only the ~'s of an inch in length. i It
is an extraordinary fact that in all the specimens the pollinia
were attached to the same peculiar spot, namely, to the outer
side of one of the two front legs, to the projection formed by
the articulation of the femur with the coxa. In one instance
alone a pollinium was attached to the outside of the femur
a little beneath the articulation. The cause of this peculiar
manner of attachment is sufficiently clear: the middle part

6 Mr. C. Darwin on the Fertilization of Orchids.

of the labellum stands so close to the anther and stigma, that
insects always enter the flower at one corner, between the
margin of the labellum and one of the upper petals ; they also
almost always crawl in with their backs turned directly or
obliquely towards the labellum. My son saw several which
had begun to crawl into the flower in a different position ; but
they came out and changed their position. Thus, standing in
either corner of the flower, with their backs turned towards
the labellum, they inserted their heads and fore legs into the
short nectary, which is seated between the two widely sepa-
rated viscid disks. I ascertained that they stand in this po-
sition by finding three dead insects, which had been per-
manently glued to the disks. Whilst sucking the nectar,
which occupies about two or three minutes, the projecting
joint of the femur stands under the large helmet-lke viscid
disk on either side; and when the insect retreats, the disk
exactly fits on, and is glued to, the prominent joint. The
movement of depression in the caudicle then takes place, and
the mass of pollen-grains projects just beyond the tibia; so
that the insect, when entering another flower, can hardly fail
to fertilize the stigma, which is situated directly beneath the
disk on either side. I know of hardly any other case in
which the whole structure of the flower is more beautifully
correlated than in the Herminium for a most peculiar manner
of fertilization.

On the movement of the pollinia in Peristylus viridis (p. 76).
—Mr. T. H. Farrer informs me that the pollinia certainly un-
dergo a movement of depression, but that this does not take
place until twenty or thirty minutes have elapsed after their
removal from the anther-cases. This length of time probably
accounts for my oversight. He asserts that, after the move-
ment of depression, the pollinia become much better adapted
to strike the stigmatic surface. He suggests that insects may
take a long time to lick up the nectar from the two naked
spots on the labellum, and through the narrow slit-like open-
ing into the nectary—and that during this time the polli-
nium becomes firmly attached, by the slow hardening of the
viscid matter, to the insect’s body, so as to be subsequently
ready to fertilize another flower when visited by the same
msect. :

On the Lepidoptera which fertilize the Gymnadenia conopsea,
and on the divergence of the pollinia (p. 82).—Mr. George
Darwin went at night to a bank where this species grows
plentifully, and soon caught Plusia chrysitis with six pollinia,
P. gamma with three, Anaitis plagiata with five, and Tri-
phena pronubawith seven pollinia attached to their proboscides.

Mr. C. Darwin on the Fertilization of Orchids. 7

I may add that he caught the first-named moth, bearing the
pollinia of this orchis, in my flower-garden, although more
than a quarter of a mile distant from any spot where the plant
grows. I state in my work that I do not understand the cause
of the divergence of the pollinia so that they are enabled to
strike the lateral stigmatic surfaces; but the explanation is
simple. The upper margin of the nectary is arched, being
formed on one side by the disk of one pollinium, and on the
other side by the other disk. Now if a moth inserts its pro-
boscis obliquely, and there are no guiding-ridges by which, as
in Anacamptis pyramidalis, a moth is compelled to insert its
proboscis directly in front, or if a bristle be inserted obliquely,
one pollinium alone is removed. In this case the pollinium
becomes attached a little on one side of the bristle or proboscis;
and its extremity, after the vertical movement of depression,
occupies a proper position for striking the lateral stigma on
the same side.

On the Gymnadenia tridentata of North America (p. 83).—
Prof. Asa Gray has published (American Journal of Science,
vol. xxxiv. 1862, p. 426, and footnote p. 260; and vol. xxxvi.
1863, p. 293) some interesting notes on the Gymnadenia
tridentata. The anther opens in the bud, and some of the
pollen invariably falls on the naked cellular tip of the rostel-
lum ; and this part, strange to say, is penetrated by the pollen-
tubes, so that the flowers are self-fertilized. Nevertheless
“all the arrangements for the removal of the pollinia by insects
(including the movement of depressien) are as perfect as in the
species which depend upon insect aid.” Hence there can be
little doubt that this species is occasionally crossed.

Habenaria or Platanthera bifolia (p. 88).—According to
Dr. H. Müller, of Lippstadt, Pl. bifolia of English authors is
the Pl. solstitialis of Boenninghausen ; and he fully agrees
with me that it must be ranked as specifically distinct from
Pl. chlorantha. Dr. Müller states that this latter species is
connected by a series of gradations with another form which
in Germany is called Pl. bifolia. He gives a very full and
valuable account of the variability of these species of Platan-
thera and of their structure in relation to their manner of fer-
tilization. (See Verhandl. d. Nat. Verein. Jahrg. xxv, III.
Folge, v. Bd. pp. 36-38.)

American species of Platanthera (p. 91).—Prof. Asa Gray
has described (American Journal of Science, vol. xxxiv. 1862,
pp. 143, 259, & 424, and vol. xxxvi. 1863, p. 292) the struc-
ture of ten American species of Platanthera. Most of these
resemble in their manner of fertilization the two British spe-
cies described by me; but some of them, in which the viscid

8 Mr. C. Darwin on the Fertilization of Orchids.

disks do not stand far apart, have curious contrivances, such
as a channelled labellum, lateral shields, &c., compelling
moths to insert their proboscides directly in front. Pl. Hookeri,
on the other hand (ibid. vol. xxxiv. 1862, p. 143), differs in a
very interesting manner: the two viscid disks stand widely
separated from each other; consequently a moth, unless of
gigantic size, would be able to suck the copious nectar without
touching either disk; but this risk is avoided in the following
manner :—The central line of the stigma is prominent, and the
labellum, instead of hanging down, as in most of the other
species, is curved upwards, so that the front of the flower is
made somewhat tubular and is divided into two halves. Thus
a moth is compelled to go to one or the other side, and its
face will almost certainly be brought into contact with one of
the disks. The drum of the pollinium, when removed, con-
tracts in the same manner as I have described under Pl. chlo-
rantha, Prot. Gray has seen a butterfly from Canada with
the pollinia of this species attached to each eye. In the case
of Platanthera flava (American Journal of Science, vol. xxxvi.
1863, p. 292), moths are compelled in a different manner to
enter the nectary on one side. A narrow but strong protube-
rance, rising from the base of the labellum, projects upwards
and backwards, so as almost to touch the column; thus the
moth, being forced to go to either side, is almost sure to
withdraw one of the viscid disks. In the allied and wonderful
Bonatea speciosa of the Cape of Good Hope there is a similar
contrivance for the samespurpose.

Platanthera hyperborea and dilatata have been regarded
by some botanists as varieties of the same species; and Prof.
Asa Gray says (Amer. Journ. of Science, vol. xxxiv. 1862,
pp- 259 & 425) that he has often been tempted to come to the
same conclusion; but now, on closer examination, he finds,
besides other characters, a remarkable physiological difference,
namely, that P/. dilatata, like its congeners, requires insect aid
and cannot fertilize itself; whilst in PZ. hyperborea the pollen-
masses commonly fall out of the anther-cells whilst the flower
is very young or in bud, and thus the stigma is self-fertilized.
Nevertheless the various structures adapted for crossing are
still present.

Fertilization of Epipactis palustris (p. 102).—My son, Mr.
W. E. Darwin, has carefully observed for me this plant in the
Isle of Wight. Hive-bees seem to be the chief agents in fer-
tilization ; for he saw about a score of flowers visited by these
insects, many of which had pollen-masses attached to their
foreheads, just above the mandibles. I had supposed that in-
sects crawled into the flowers; but hive-bees are too large to

Mr. C. Darwin on the Fertilization of Orchids, 9

do this; they always clung, whilst sucking the nectar, to the
distal and hinged half of the labellum, which was thus pressed
downwards. Owing to this part being elastic and tending to
spring up, the bees, as they left the flowers, seemed to fly
rather upwards; and this would favour, in the manner explained
by me, the complete withdrawal of the pollen-masses, quite as
well as an insect crawling out of the flower in an upward
direction. Perhaps, however, this upward movement may not
be so necessary as I had supposed; for, judging from the point
at which the pollen-masses were attached to the bees, the
back part of the head would press against, and thus lift up, the
blunt, solid, upper end of the anther, thus freeing the pollen-
masses,

Various other insects besides hive-bees visit this Epipactis.
My son saw several large flies (Sarcophaga carnosa) haunting
the flowers; but they did not enter in so neat and regular a
manner as the hive-bees; nevertheless two had pollen-masses
attached to their foreheads. Several smaller flies (Cælopa
frigida) were also seen entering and leaving the flowers, with
pollen-masses adhering rather irregularly to the dorsal surface
of the thorax. Three or four distinct kinds of Hymenoptera
(one of small size being Crabro brevis) likewise visited the
flowers; and three of these Hymenoptera had pollen-masses
attached to their backs. Other still more minute Diptera,
Coleoptera, and ants were seen sucking the nectar; but these
insects appeared to be too small to transport the pollen-masses,
It is remarkable that some of the foregoing insects should
visit these flowers; for Mr. F. Walker informs me that the
Sarcophaga frequents decaying animal matter, and the Cælopa
haunts seaweed, occasionally settling on flowers; the Crabro
also, as I hear from Mr. F. Smith, collects small beetles ( Hal-
tice) for provisioning its nest. It is equally remarkable, see-
ing how many kinds of insects visit this Æpipactis, that, al-
though my son watched for some hours on three occasions
hundreds of plants, not a single humble-bee alighted on a
flower, though many were flying about. In a footnote I have
given the results of experiments made by Mr. More, by cutting
off the distal and hinged half of the labellum, in order to as~
certain how far this part is important. He has now repeated
the experiment on nine additional flowers : of these, three did
not produce seed-capsules; but this may have been accidental.
Of six capsules which were produced, two contained about as
many seeds as the capsules of unmutilated flowers on the same
plant; but four capsules contained much fewer seeds. The
seeds themselves were well-formed. These experiments, as
far as they go, support the view that the distal part of the

10 Mr. C. Darwin on the Fertilization of Orchids.

Jabellum plays an important part in leading insects to enter
and leave the flower in a proper manner for fertilization. __

Fertilization of Epipactis latifolia (p. 104) —AlIthough this
orchis is not common in the vicinity of Down, by a fortunate
chance several plants sprang up in a gravel walk close to my
house, so that I have been able to observe them during several
years, and have thus discovered how they are fertilized. Al-
though hive-bees and humble-bees of many kinds were con-
stantly flying over the plants, I never saw a bee or any Dip-
terous insect visit the flowers; whilst, on the other hand, I
repeatedly observed each year the common wasp (Vespa syl-
vestris) sucking the nectar out of the open cup-shaped label-
lum. I thus saw the act of fertilization effected by the pollen-
masses being removed and carried on the foreheads of the
wasps to other flowers. Mr. Oxenden also informs me that
a large bed of E. purpurata (which is considered by some
botanists a distinct species, and by others a variety) was
frequented by “swarms of wasps.” It is very remarkable
that the sweet nectar of this Epipactis should not be attractive
to any kind of bee. If wasps were to become extinct in any
district, so would the Epipactis latifolia.

Dr. H. Müller of Lippstadt has published (Verhandl. d. Nat.
Ver. Jahrg. xxv. IIL. Folge, v. Bd. pp. 7-36) some very im-
portant observations on the differences in structure and in the
manner of fertilization, as well as on the connecting gradations,
between Epipactis rubiginosa, microphylla, and viridiflora.
The latter species is highly remarkable by the absence of a
rostellum, and by being regularly self-fertilized. This latter
circumstance follows from the incoherent pollen of the lower part
of the pollen-masses emitting, whilst still within the anther-
cells, pollen-tubes, which penetrate the stigma; and this oc-
curred even in the bud state. This species, however,is probably
visited by insects, and occasionally crossed; for the labellum
contains nectar. Æ. microphylla is equally remarkable, by
being intermediate in structure between Æ. latifolia, which is
always fertilized by the aid of insects, and Æ. viridiflora,
which does not necessarily require any such aid. The whole
of this memoir by Dr. H. Miiller deserves to be attentively
studied.

Cephalanthera grandiflora (p. 108).—During the year 1862,
the flowers of this orchis appeared to have been visited much
less frequently by insects than during the previous years; for
the masses of pollen were seldom broken down. Although I
have repeatedly examined the flowers, I have never seen a
trace of nectar; but some appearances lead me to suspect that
the ridges within the base of the labellum are attractive to

Mr. C. Darwin on the Fertilization of Orchids. 11

Insects, and are gnawed by them, as in the case of many
Vande and other exotic orchids.

Goodyera repens (p. 114).—Mr. R. B. Thomson informs me
that in the north of Scotland he saw many humble-bees visit-
ing the flowers and removing the pollen-masses, which were
attached to their proboscides. The bee sent was Bombus pra-
torum. This species grows also in the United States; and
Prof. Gray (Amer. Journ, of Science, vol. xxxiv. 1862, p. 427)
confirms my account of its structure and manner of fertiliza-
tion, which is likewise applicable to another and very dis-
tinct species, namely, Goodyera pubescens. Prof. Gray states
that the passage into the flower, which is at first very narrow,
becomes, as I suspected, more open during its older state.
Prof. Gray believes, however, that it is the column, and not
the labellum, which changes its position.

Spiranthes autumnalis (p. 123).—As in the case of the
Goodyera, Prof. Gray feels confident that it is the column which
moves from the labellum as the flower grows older, and not,
as I had supposed, the labellum which moves from the column.
He adds that this change of position, which plays so important
a part in the fertilization of the flower, “is so striking that
we wonder how we overlooked it” (Amer. Journ. of Science,
vol. xxxiv. p. 427).

On the rostellum of Listera ovata not exploding spontaneously
(p.149).—I have covered up some additional plants, and found
that the rostellum lost its power of explosion in about four days,
the viscid matter then turning brown within the loculi of the
rostellum. The weather at the time was unusually hot, and
this may have hastened the process. After the four days had
elapsed, the pollen had become very incoherent and some had
fallen on the two corners, or even over the whole surface, of
the stigma, which was penetrated by the pollen-tubes. Hence,
if insects should fail to remove the pollinia by causing the
explosion of the rostellum, this orchid certainly seems capable
of occasional self-fertilization. But the scattering of the in-
coherent pollen was largely aided by, and perhaps wholly de-
pended on, the presence of Thrips—insects so minute that
they could not be excluded by any net.

Listera cordata (p. 152).—Prof. Dickie has been so good as
to observe the flowers on living plants. He informs me that,
when the pollen is mature, the crest of the rostellum is di-
rected towards the labellum, and that, as soon as touched, the
viscid matter explodes, the pollinia becoming attached to the
touching object; after the explosion, the rostellum bends
downwards and spreads out, thus protecting the virgin stig-
matic surface; subsequently the rostellum rises and exposes

12 Mr. C. Darwin on the Fertilization of Orchids.

the stigma; so that everything here goes on as I have de-
scribed under Listera ovata. The flowers are frequented by
minute Diptera and Hymenoptera.

On the self-fertilization of Neottia nidus-avis, and on the
rostellum not exploding spontaneously (p. 153).—1 covered up
with a net several plants, and after four days found that the
rostellum had not spontaneously exploded, and had already
almost lost this power. The pollen had become incoherent,
and in all the flowers much had fallen on the stigmatic sur-
faces, which were penetrated by pollen-tubes. The spreading
of the pollen seemed to be in part caused by the presence of
Thrips, many of which minute insects were crawling about
dusted all over with pollen. The covered-up plants produced
plenty of capsules, but these were much smaller and contained
much fewer seeds than the capsules produced by the adjoining
uncovered plants. I may here add that I detected on the crest
of the rostellum some minute rough points, which seemed
particularly sensitive in causing the rostellum to explode.

Dr. H. Miiller, of Lippstadt, informs me that he has seen
Diptera sucking the nectar and removing the pollinia of this
plant.

On the self-fertilization of certain Epidendree (p. 166).—
Dr. Criiger says (Journ. Linn. Soc. vol. viii. Botany, 1864,
p. 131) that “we have in Trinidad three plants belonging to
the Epidendrese (a Schomburgkia, Cattleya, and Epidendron)
which rarely open their flowers, and are invariably impreg-
nated when they do open them. In these cases it is easily
seen that the pollen-masses have been acted on by the stig-
matic fluid, and that the pollen-tubes descend from the pollen-
masses 77 situ down into the ovarian canal.” Mr. Anderson,
a skilful cultivator of orchids in Scotland, informs me (see also
‘Cottage Gardener,’ 1863, p. 206) that with him the flowers
of Dendrobium eretaceum never expand, and yet produce
capsules with plenty of seed, which, when examined by me,
was found to be perfectly good. These orchids make a near
approach to those dimorphic plants (as Oxalis, Ononis, and
Viola) which habitually produce open and perfect, as well as
closed and imperfect flowers.

On the slow movement of the pollinia in Oncidium (p. 189).
—Mr. Charles Wright, in a letter to Prof. Asa Gray, states
that he observed in Cuba a pollinium of an Oncidium attached
to a Bombus, and he concluded at first that I was completely
mistaken about the movement of depression ; but after several
hours the pollinium moved into the proper position for fertilizing
the flower. i

Manner of fertilization of various exotic Orchids (p. 189).

Mr. C. Darwin on the Fertilization of Orchids. 13

—I may here remark that Delpino (Fecondazione nelle Piante,
Firenze, 1867, p. 19) says he has examined flowers of Vanda,
Epidendron, Phaius, Oncidium, and Dendrobium, and con-
firms my general statements. The late Prof. Bronn, in his
German translation of this work (1862, p. 221), gives a de-
scription of the structure and manner of fertilization of Stan-
hopea devoniensis.

Sexes of Acropera not separated (p. 206).—I have committed
a great error about this genus, in supposing that the sexes
were separate. Mr. J. Scott, of the Royal Botanic Garden of
Edinburgh, soon convinced me that it was an hermaphrodite,
by sending me capsules containing good seed, which he had
obtained by fertilizing some flowers with pollen from the same
plant. He succeeded in doing this by cutting open the stig-
matic chamber, and inserting the pollen-masses. My error
arose from my ignorance of the remarkable fact that, as shown
by Dr. Hildebrand ( Botanische Zeitung, 1863, Oct. 30 et
seq., and Aug. 4, 1865), in many orchids the ovules are not
developed until several weeks or even months after the pollen-
tubes have penetrated the stigma. No doubt if I had exa-
mined the ovaria of Acropera some time after the flowers had
withered, I should have found well-developed ovules. In
many exotic orchids besides Acropera (namely, in Gongora,
Cirrhæa, Acineta, Stanhopea, &c.), the entrance into the stig-
matic chamber is so narrow that the pollen-masses cannot be
inserted without the greatest difficulty. How fertilization is
effected in these cases is not yet known. That insects are the
agents there can be no doubt; for Dr. Criiger saw a bee (Lu-
glossa) with a pollinium of a Stanhopea attached to its back ;
and bees of the same genus continually visit Gongora. Fritz
Müller has observed, in the case of Cirrhwa (Bot. Zeitung,
Sept. 1868, p. 630), that if one end of the pollen-mass be in-
serted into the narrow entrance of the stigmatic chamber, this
part, from being bathed by the stigmatic fluid, swells, and the
whole pollen-mass is thus gradually drawn into the stigmatic
entrance. But, from observations which I have made on
Acropera and Stanhopea in my own hot-house, I suspect that,
with many of these orchids, the pedicel with the narrow end
of the pollinium, and not the broad end, is ordinarily inserted
into the stigmatic chamber. By thus placing the pollinium,
I have occasionally succeeded im fertilizing some of these
orchids, and have obtained seed-capsules.

Structure and fertilization of the Vandeæ ce. of Brazil
(p. 210).—F ritz Müller has sent me many letters containing an
astonishing number of new and curious observations on the
structure and manner of cross-fertilization of various orchids

14 Mr. C. Darwin on the Fertilization of Orchids.

inhabiting South Brazil. I much regret that I have not here
space or time to give an abstract of his many discoveries,
which support the general conclusions given in my work;
but I hope that he will some day be induced to publish a full
account of his observations.

Fertilization of Catasetum (p. 211).—It has been highly
satisfactory to me that my observations and predictive conclu-
sions in regard to Catasetum have been fully confirmed by the
late Dr. Criiger, the Director of the Botanic Gardens of Tri-
nidad, in letters to me and in his paper in the ‘ Journal of the
Linnean Society’ (vol. viii. Bot. 1864, p. 127). He sent me
specimens of the bees, belonging to three species of Huglussa,
which he saw gnawing the inside of the labellum. The pol-
linia, when ejected, become attached to, and lie flat on, the
backs of the bees, on the hairy surface of the thorax. Dr.
Criiger has also proved that I was correct in asserting that
the sexes of Catasetum are separate, for he fertilized female
flowers with pollen from the male plants; and Fritz Müller
effected the same thing with Catasetum mentosum in South
Brazil. Nevertheless, from two accounts which I have re-
ceived, it appears that Catasetum tridentatum, though a male
ete occasionally produces seed-capsules ; but every botanist
snows that this occasionally occurs with the males of other
dicecious plants. Fritz Miller has given (Botanische Zeitung,
Sept. 1868, p. 630) a most interesting account, agreeing with
mine, of the state of the minute pollinia in the female plant :
the anther never opens, and the pollen-masses are not attached
to the viscid disks, so that they cannot be removed by any
natural means. The pollen-grains, as so generally occurs with
rudimentary organs, are extremely variable in size and shape.
Nevertheless the grains of the rudimentary pollen-masses be-
longing to the female plant, when applied (which can never
naturally occur) to the stigmatic surface, emitted their pollen-
tubes! This appears to me a very curious instance of the
slow and gradual manner in which structures are modified ;
for the female pollen-masses, included within an anther which
never opens, are seen still partially to retain their former
powers and function.

Mormodes luxatum (p. 265).—I have now examined another
age of Mormodes, the rare M. luxatum, and I find that the
chief points of structure, and the action of the different parts,
including the sensitiveness of the filament, are the same as
in M. ignea. The cup of the labellum, however, is much
larger, and is not pressed down firmly on the filament on the
summit of the column. This cup probably serves to attract
insects, and, as in Catasetum, is gnawed by them. The flowers

Mr. C. Darwin on the Fertilization of Orchids. 15

are asymmetrical to an extraordinary degree, the right-hand
and left-hand sides differing much in shape.

Cycnoches ventricosum (p. 265).—The plant described in my
work as a second species of Mormodes proves to be Cycnoches
ventricosum. I first received from Mr. Veitch some flower-buds,
from which the section (fig. xxx.) was taken ; but subsequently
he sent me some perfect flowers. The yellowish-green petals
and sepals are reflexed ; the thick labellum is singularly shaped,
with its upper surface convex, like a shallow basin turned
upside down. The thin column is of extraordinary length, and
arches like the neck of a swan over the labellum ; so that the
whole flower presents a very singular appearance. In the sec-
tion of the flower, given in my work, we see the elastic pedicel
of the pollinium bowed, as in Catasetum or Mormodes ; but at
the period of growth represented in the figure the pedicel was
still united to the rostellum, the future line of separation being
shown by a layer of hyaline tissue indistinct towards the upper
end of the disk. The disk is of gigantic size, and its lower
end is produced into a great fringed curtain, which hangs in
front of the stigmatic chamber. The viscid matter of the disk
sets hard very quickly, and changes colour. The disk ad-
heres to any object with surprising strength. The anther is
very different in shape from that of Catasetum or Mormodes,
and apparently would retain the pollen-masses with greater
force. A part of the filament of the anther, lying between
two little leaf-like appendages, is sensitive; and when this
part is touched, the pollinium is swung upwards, as in Mor-
modes, and with sufficient force, if no object stands in the
way, to throw it to the distance of an inch. An insect of
large size alights probably on the labellum, for the sake of
gnawing the convex surface, or perhaps on the extremity of
the arched and depending column, and then, by touching the
sensitive point, causes the ejection of the pollen-masses, which
are affixed to its body and thus transported to another flower
or plant.

Fertilization of the Arethusex (p. 269).—Epipogium Gmelini
has been the subject of an admirable memoir (Ueber den Blii-
thenbau, &c., Göttingen, 1866) by Dr. P. Rohrbach, who
has shown how the flowers are fertilized by Bombus lucorum.
With respect to another genus belonging to this same tribe,
namely Pogonia, Dr. Scudder of the United States has de-
scribed (Proc. Boston Nat. Hist. Soc. vol. ix. 1863, p. 182)
the manner in which it is fertilized by the aid of insects.

Cypripedium (p. 274).—Prof. Asa Gray, after examining
several American species of Cypripedium, wrote to me (see
also Amer. Journ. of Science, vol. xxxiv. 1862, p. 427) that

16 Mr. C. Darwin on the Fertilization of Orchids.

he was convinced that I was in error, and that the flowers
are fertilized by small insects entering the labellum through
the large opening on the upper surface, and crawling out by
one of the two small orifices close to either anther and the
stigma. Accordingly I caught a very small bee which seemed
of about the right size, namely the Andrena parvula (and this
by a strange chance proved, as we shall presently see, to be
the right genus), and placed it in the labellum through the
upper large opening. The bee vainly endeavoured to crawl
out again the same way, but always fell backwards, owing to
the margins being inflected. The labellum thus acts like one
of those conical traps with the edges turned inwards, which are
sold to catch beetles and cockroaches in the London kitchens,
Ultimately the little bee forced its way out through one of the
small orifices close to one of the anthers, and was found when
caught to be smeared with the glutinous pollen. I then again
put the same bee into the labellum; and again it crawled out
through one of the small orifices. I repeated the operation
five times, always with the same result. I then cut away the
labellum, so as to examine the stigma, and found it well
smeared over with pollen. Delpino (Fecondazione &e. 1867,
p: 20) with much sagacity foresaw that some insect would be
discovered to act in the manner Just described; for he argued
that if an insect were to insert its proboscis, as I had supposed,
from the outside through one of the small orifices close to one
of the anthers, the stigma would be fertilized by the plant’s
own pollen; and in this he did not believe, from having
confidence in what I have often insisted on—namely, that all
the contrivances for fertilization are arranged so that the
stigma shall receive pollen from a distinct flower or plant.
But these speculations are now all superfluous ; for, owing to
the admirable observations of Dr. H. Müller, of Lippstadt
(Verh. d. Nat. Ver. Jahrg. xxv. III. Folge, v. Bd. p. 1), we
actually know that Cypripedium calceolus in a state of nature
is fertilized by two species of Andrena, in the manner above
supposed.

On the relation between the more or less viscid condition of
the pollen and stigma in Cypripedium (p. 276).—The relation
between the state of the pollen and stigma, which I have
pointed out in my work, is strongly confirmed by Prof. Gray's
statement (Amer. Journ. of Science, vol. xxxiv. 1862, p. 428),
namely, that in C. acaule the pollen is much more granular or
less viscid than in other American species of the genus, and in
this species alone the stigma is slightly concave and viscid!
Dr. Gray adds that in most of the species the broad stigma
presents another remarkable peculiarity, “in being closely

Mr. C. Darwin on the Fertilization of Orchids. 17

beset with minute, rigid, sharp-pointed papillee, all directed
forwards, which are excellently adapted to brush off the pollen
from an insect’s head or back.”

The use of the copious fluid contained within the labellum
of Coryanthes (p. 278).—The Coryanthes macrantha is per-
haps the most wonderful of all known orchids, even’ more
wonderful in structure and function than Catasetum. Its
manner of fertilization has been described by Dr. Criiger in
the ‘Journal of the Linnean Society’ (vol. viii. Bot. 1864,
p. 180), and in letters to me. He sent me bees, belonging to
the genus Huglossa, which he saw at work. The fluid in the
bucket formed by the basal part of the labellum is not nectar
and does not attract insects, but serves, by wetting their
wings, to prevent them from crawling out except through the
small passages close to the anther and stigma, Thus the
secretion of fluid in this orchis serves exactly the same end as
the inflected margins of the labellum in Cypripedium.

On the evidence that Insects visit many exotic Orchids in order
to gnaw parts of the labellum, and not for the sake of nectar
(p. 284).—It has been highly satisfactory to me that this hypo-
thesis has been fully confirmed. In the West Indies, Dr. Criiger
witnessed humble-bees of the genus Huglossa gnawing the
labellum of Catasetum, Coryanthes, Gongora, and Stanhopea ;
and Fritz Miller has repeatedly found, in South Brazil, the
prominences on the labellum of Oncidium gnawed. We are
thus enabled to understand the meaning of the various extra-
ordinary crests and projections on the labellum of various
exotic orchids; for they invariably stand in such a position
that insects, whilst gnawing them, will be almost sure to
touch the viscid disks of the pollinia, and thus remove them.

Bonatea speciosa (p. 305).—The manner of fertilization of
this extraordinary orchis has now been fully described by Mr.
R. Trimen in the ‘ Journal of the Linnean Society’ (vol. ix.
Bot. 1865, p. 156). A projection rising from the base of the
labellum is one of its most remarkable peculiarities, as an in-
sect is thus compelled to insert its proboscis on one side, and
thus to touch one of the two widely separated and projecting
viscid disks. Mr. J. P. Mansel Weale has also published
(ibid. vol. x. 1869, p. 470) analogous observations on a second
species, viz. Bonatea Darwinit. Mr. Weale caught a skipper-
butterfly (Pyrgus elmo) quite embarrassed by the number of
pollinia belonging to this orchis which adhered to its sternum.
I do not know of any other case in which the pollinia adhere
to the sternum of a Lepidopterous insect.

On the nature of the contraction which causes the pollinia,

after their removal ‘from the anther, to change their position
B

18 Mr. C. Darwin on the Fertilization of Orchids.

(p. 838).—In Orchis hircina, I clearly saw, under the micro-
scope, the whole front of the viscid disk become depressed as the
two pollinia together underwent the movement of depression.

Number of seeds (p. 344)—The number of seeds produced
by Orchis maculata, as given in my work, is small in com-
parison with that produced by some foreign species. I have
shown (Variation of Animals and Plants under Domestication,
vol. ii. 1868, p. 379), on the authority of Mr. Scott, that a
single capsule of Acropera contained 371,250 seeds ; and the
species produces so many flowers and racemes, that a single
plant probably sometimes produces as many as 74 millions of
seeds in the course of a single year. Fritz Miiller carefully
estimated, by weighing, the number of seeds in a single capsule
of a Mavrillaria in South Brazil, and found the number
1,756,440. The same plant sometimes produces half-a-dozen
capsules.

Number of pollen-grains (p. 355).—I have endeavoured to
estimate the number of pollen-grains produced by a single
flower of Orchis mascula. There are two pollen-masses; in
one of these I counted 153 packets of pollen; each packet
contains, as far as I could count, by carefully breaking it up
under the microscope, nearly 100 compound grains; and each
compound grain is formed of four grains. By multiplying
these figures together, the product for a single flower is about
120,000 pollen-grains. Now we have seen that in the allied
O. maculata a single capsule produced about 6,200 seeds ; so
that there are nearly twenty pollen-grains for each ovule or
seed. As a single flower of a Mazillaria produced 1,756,000
seeds, it would produce, according to the above ratio, nearly
34 million pollen-grains, each of which, no doubt, includes
the elements for the reproduction of every single character in
the mature plant!

Enumeration of the Orchideæ which, as at present known,
habitually fertilize themselves (p.358).—We have now seen
that self-fertilization habitually occurs, in a more or less perfect
manner, in one of the species of Ophrys, of Neotinea, Gymna-
denia, Platanthera, Epipactis, Cephalanthera, Neottia, and in
those Epidendree and in Dendrobium which often produce
flowers that never expand. No doubt other cases will here-
after be discovered. Self-fertilization seems to be more per-
fectly secured in Ophrys apifera and in Neotinea intacta than
in the other species. But it deserves especial notice that in
all these orchids structures are still present, not in a rudimen-
tary condition, which are manifestly adapted for the transport
by insects of the pollen-masses from one flower to another.
As I have elsewhere remarked, some plants, both indigenous

Mr. C. Darwin on the Fertilization of Orchids. 19

and naturalized, rarely or never bear flowers, or, if they do bear
towers, these never produce seed. But no one doubts that
it is a general law of nature that phanerogamic plants should
produce flowers, and that these flowers should produce seed.
When they fail to do this, we believe that such plants would
perform their proper functions under different conditions, or
that they formerly did so and will do so again. On analogical
grounds I believe that the few orchids which do not now inter-
cross, either did formerly intercross (the means for effecting
this being still retained) or that they will do so at some
future period under different conditions, unless, indeed, they
become extinct from the evil effects of long-continued close
interbreeding.