Notes on Pronuba and Yucca Fertilization

150

NOTES ON PRONUBA AND YUCCA

POLLINATION.*

BY PKOF. C. V. RILEY.

Partly because of

more

_pressingduties, partlybecause ofa desire to

make some

_specialexperiments, butchiefly in the hope ^that(after the _fruiting season of the dehiscentYuccas

was

over, and Mr. Hulst had beenableto

make more

careful observations) he

would

himself gracefully

amend

his opinions^toaccord with the facts,^I have deferred answering ^till

now

the remarks by Mr. Hulst on pp. 236-238 of^{vol. ii,}Ent.

Amer. The

matter

is tooimportant^todrop,andIhavetoo

much

_regardfor

my

^criticperson- ally,and hope^{for hisfuture}entomologically, not^todo

what

little Icanto check anunfortunatetendency^tohasty

work

andconclusion, noticeablein this as in

some

other ofhis latewritings.

Mr. Hulst "confessesthecorn"inreferenceto

my

^first complaint,and

is inclined toblame_{the report}forhis misrepresentations an inclination which would have

more

of

my sympathy

^{were henoteditor}of the paper.

It_is,however, ^far

more

_important,fromthe scientific side, thathecon- fesstothe justness of

my

^second indictment, and itisto this endthatI

returnto the_subject.

Mr. Hulstadheres tohis belief"_thatthere

must

be very extensive ^fer- tilization of the dehiscent _species of

Yucca

_by the agencies of bees and otherinsects."

He

does notbring ^{forth a}singledefinite factorobserva- tionof actual pollination^to proveor sustain thebelief,butrestsitonthe followinggrounds^:

ist.

That Meehan

foundthat the

mere

application ofpollen^tothe_papil- loseapex^{of the}stigma ^issufficient forfertilization.

2d.

That

he_(Hulst)has seenhoney-bees ^{within the}open^{as wellas the} partlyopenflowers, as alsootherinsects,Aphides andCoccinellidcebeing particularlymentioned.

3d.

That

notoneinten of the capsules subsequentlyexamined by

him showed

the larva.

4th.

That

heis informed thatdehiscent_speciesof

Yucca

doripen seeds in Europe.

Such

arethe negativearguments

upon which

^{herests hisbelief intheface} ofallttizfacts^Ihave put on ^record. Let us consider the former_briefly in theirorder.

ist.

My good

^friend

Meehan

has written

much

on thefertilizationof

*In explanation of the controversial nature of^this communication, ^it becomes _necessaryto refer to adispute on this subject between theRev.

G.D. Hulstand myself ^inthe

columns

ofEntomologica

Americana

dur- ing the

summer

of_1887.

The

communication ^isareplytoMr.Hulst'slast publicationon the_subject,and ispresented verbatimetliteratimas writ- ten on

my way

^to

Europe

ⁱⁿ

August

^{of that} year,and as mailed to

him

from England. Mr. Hulstiseditorof the aforesaid journal,andexercised his editorialprerogativeⁱⁿdeclining^topublish thecommunication. Ihave, therefore, concludedtopresent thepaper^totheSociety, since^itdiscusses matters of considerablescientific interest.

151

Yucca much,

too, that has not

shown

the keenest penetration nor the strictestaccuracy. But, in candidly admitting^{his errors}

when shown

to be

wrong

(ashe has donetothe writer and, ^I have reason to believe, to Mr. Hulst,

who

_sought his support^{in the belief}herecombated), he^has proved himself^{to be the}true naturalist. I

am

familiarwith his experi- ments, having^{witnessed the}results,and can best express

my ^own

^opin-

ionby quoting from^{a letter}fromthelateDr. G.

Englemann

(writtenJan.

10, 1881), in which

among

other things he says: ^{* * *}

"As

^to

Mee-

han's operations ^I have seen myself^{the fine,} large, well-filled pods^of Yuccaangustifolia ^raised by

him

_by hisartificial method.

He

_says he punches an anther ^into the stigmatic cavity.

Whether

he or

anybody

elsecould distinguish whether the pollen adheresonly ^tothe papillose (not stigmatose)apex^orgets into the_liquorthatfillsthe_cavity

when

the stigma ^is ready ^{toconceive,isa} question (orno _question)!" Meehan's experiments were

made

ona 'species inwhich, ^asIhaveelsewhereshown, the stigma ^isshorter and the stigmatic liquor

more

abundant than in Yuccafilamentosa,and it

may

^{be thatfortheseor}other reasonsitis

more

easily pollinized

by hand

^orby^other

means

thanby Pronuba. ButIhave followedup^hisexperiments and

made many

^othersduringthe past seven years,onfilamentosa andaloifolia,with resultsthatconvince

me

thatap- plication of the pollen^tothe papillose apicesonly^{is not}sufficient toin- sure fructification, at least in those_species.

My

experiments have been

made

inthe

afternoon^ evening,and

morning;

^{withflowers one}day, two days, andthree days^afteropening; with pollenfrom the

same

floweror fromother flowerseitheron the

same

or otherracemes; by touching^the mere_apiceswith antheror brush, and byforcing the pollenby^eithercon- veyance^into the stigmatic^tube. In these experiments,

which

havenot yet been _published, and

which

^itis unnecessary ^{to detail here,I} have endeavored to guard against ^all influences, such as the condition of the plantand the weather,which might^{affectorvitiate,theresults.} These

may

^be

summed

_upthus^:

(1) Dr.Engelmann's ^{limitof time} during which fertilization

may

^take

place

must

beextendedso as to include the second evening,and even the second morning, ^aftertheopening^{of theflower.}

(2)

No

seed hasbeen produced by merely touchingthe apices of thestigma with the_pollen, thoughpartial fertilization

may

take placeand cause the growth^{of thefruitfora}varyingperiod, generallyonly^threeor four days.

When

_{the pollen} ^isthrustintothe tube _(the

mode

of conveyance

making

littledifference) fertilization^is

much more

certain,butevenhereisrarely sufficient toproduceripe seed,theupperpart of thepod ^oftenfillingwell, but the basal part notfilling,and at last withering ^{so thatthe}fruit ulti-

mately^{falls off}before ripening.

The

conclusionis inevitablethat angustifolia ^is

more

susceptible^toarti- ficial pollination than the _species which I experimented ^with, and that Pronubafarexcels

man

in the perfectionwithwhichsheperforms^theact.

She has the

power

^offertilizingall "theovules,atwhich nb onewill

wonder

who

has_carefullywatched her,becausetheactof pollination ^isnormally

152

repeated^severaltimes,firstfromoneof the anglesbetweenthe_apices,then from _another,and,as Prof.

Wm.

Trelease has shown,thetongue^isused, inaddition tothetentacles, topushthe pollen

down

tothebottom of the tube.

2d. Ihave

made

careful search the past

summer,

and have had

my

^asso-

ciates,Messrs.

Howard,

Pergande, and Lugger, ^{assist in the search for} honey-bees^inoraboutthe

Yucca

flowersinWashington. There wereover 200stalksunderobservation, most ^of

them

of easy accessonthegrounds of the

Department

of Agriculture. Neither of the threegentlemen

men-

tioned detectedany^{bees,butIsucceeded}on two _occasions,andeach time between₉and 10a.m.,infindinga singlebee_flyingabouttheflowers. In neither casedidthe bee

make

any attempt ^to enter,butineachitprobed around the outer base of the flower in search for nectar, and soon left evidently without being ^{able to} getmuch. Thesefacts I record,not in

any

way

^{to cast discredit on Mr.} Hulst's statement, but rather ^to

show how

_verydifferentfromhis

own

has been

my

experience in this direction, both inSt. Louis and Washington.

Not

that I place

much

faith in the constancy of ^bees,whichare

known

tobe

somewhat

fickle in their tastes according^toseason or colony,a fact thatmaj-accountforthedifference in ourexperience,^as

may

^{also the} presumption ^that Apismellifica ^is

more

abundantinBrooklyn than ⁱⁿ Washington, ^or, again, the

known

factthat Tticcaangustifolia ^isless scant in nectar than its filamentose congener.

Be

that as itmay, our Apis ^hasplainly, sofarasobserved,beenafternec- tar, andhas

shown

nodisposition whatevertogonear the stigma,andthis factis,asI havelearned, corroboratedby^Professors

Cook

and_Beal,of the Michigan State Agricultural College,where, ^{for the} first time_{this year,} theyhaveobserved honey-bees about^the

Yucca

flowers. Itisfurthercor- roborated by experiment which^I

made

this

summer

of confining bees^to the flowers withinagauze^enclosure.

As

for pollination by ^other insects, Chauliognathus pennsylvanicus, whichfeedson both _pollen and the nectar,^is the most

common

_species

foundintheflowers,and by^virtueof these habitsand itspeculiarlymodi-

fied mouth-parts,^is

most

tobe suspected; yet^Ihave _carefullywatched it for years,only^tobeconvincedthatitnevereither assistsorcompetes^with Pronubain theactof pollination.

3d. This

argument

has alreadybeendisposed ofⁱⁿ

my

previous

commu-

nication_(vol. ii,p. 238,

summary

iv),and itisonlynecessary^toadd, that untilMr. Hulstis

more

_exact,and willtelluswhatproportion of^hispods containingnolarvaealso

showed

no_{signs of}oviposition(t.e.,

how many

were_perfectwithout_{sign of}punctureor constrictionorirregularityabout the middle),

we

shall noteven

know how many

^{the little}

^moth

pollinized without_gettingachancetoperform ^theother(toher)important^act.

4th. This iscontrary^to

my ^own

experience ⁱⁿ Europe, and ^{to all au-} thoritativerecord familiartome, anduntilMr. Hulst_{gives us}hisauthority and the evidence, ^itwere sherewasteof timetofurther discuss the_point.

I havethus disposed of^{all the valid} arguments brought^forwardby Mr.

WASHINGTON. 153

Hulsttosustain his position on this matter. I

may

briefly notice, how- ever, a^littlesatire whichhe indulges ^{in at}

my

expense, and_{a quite}irrele- vant assertionwhich happens^{also tobeincorrect.}

As

one_deeplyinterested inapicultureanda practicalbee-keeper twenty- seven years ago,^itwas, perhaps, unpardonable ⁱⁿ

me

not _{to qualify}the statementaboutbees notbeing^{attracted to white flowers.} Both Miiller, in his"

Alpenblumen," and Lubbock, ⁱⁿ "Ants,Bees, Wasps,"etc., have

shown

that bees_preferblueand _purpletowhite flowers,and thisis

what was meant

on the face of

my

language, ^{so to} cpeak; butMr. Hulst has naturally

made

the

most

of the _lapsus, and scored a point where _every other point^isagainsthim.

The

assertionwhichI wouldcall attention _to, and which isentirely be- sidethequestion^{at issue,is that}

"we

areindebted toDr.

Engelmann

^for the discovery of the ^fact that

Pronuba

isan agent ^{in the} fertilization of Yucca."

Whatever may

^{haveled Mr. Hulstto}

^make

this assertion, ^{it is} simply untrue,and the_facts, whichI

may

^as well putonrecord here,arethese^: In June, 1872, Dr.

Engelmann, who

then

knew

fullwellthat

Yucca

needed extraneousaid in fertilization, called

my

^{attention to thisfact, andtothe}

furtherfactthatinsects, especiallywhite

moths

andsoldier-beetles(Chau- liognathns),were

common

intheflowers.

He made

noobservationswhat- ever

upon

insect pollination, but wished

me

to study the question.

The

discovery^that

Pronuba was

theagent

was my

own,^as wereallthe subse- quentdiscoveriesin referencetotheinsect

made

thatyear; but they were always

communicated

tohim, andoften sharedwith andwitnessedby him.

My

^firstpaper onthe subjectwasreadinAugust,1872,before theA.A.A.S., atits

Dubuque

(Iowa)meeting,and _presentedtothe

Academy

^ofSciences

ofSt.Louisatthemeeting^forSeptember^2,1872. Dr.Engelmann's

"Notes

onthegenus

Yucca

^"were_presented tothe

same Academy

September^16, 1872. Both_papersareprinted^{in vol.iiiof}theTransactions of the

Academy,

Dr. Engelmann's preceding, because leading up ^{tomine. In his} paper Dr. E. says^:

"The

_suspected insects were handed overto

my

^{friend Mr.}

C. V. Riley,

who

thereupon took upthe zoological part of the investiga- tion,the surprisingly interesting^resultsofwhichare detailedby

him

inthe succeedingpaper" (Trans., etc., iii,p. 19),andIdistinctlyexpress

my

^in-

debtednessto

him

^"fordrawing

my

^{attentiontothefactthat}the plants of thisgenus

must

_relyon

some

insector otherfor fertilization." Itisquite probable ^that but for Dr. Engelmann's suggestion ^I should never have

made

theinvestigations,and he shouldsharewith

me

whatever honorat- tachestothe discovery. ^{If this is} what Mr. Hulst

means

hislanguage^is unfortunate. Dr.

Engelmann

^was,during

my

^{residenceinSt.Louis,atonce}

my

^friend, companion, and masterⁱⁿ natural history matters,andI have too

much

reverence forhis

memory

^{toallowtopass}unchallenged what he himselfwould_repudiatewere hestill

among

^us.

^As

^{soonasIhadlearned}

that

Pronuba

wastheagent he^{senta brief}

announcement

tothe Bulletin of theTorrey^Botanical Club(vol. iii, No. _7,July, 1872,p.33)rather_hastily

154

referring tothe insect as "_awhite

moth

of the genusTortrix,"andin a subsequent communication (ibid., August, 1872,p. 37) he corrected the errorandrecorded

some

furtherfacts in thelife-history of theinsect. In neithercase was there

any

claim of individual discovery of the entomo- logical^facts,and these

announcements must

be read in the _light of his subsequent

more

deliberatelanguage which^I have_quoted.

In conclusion,havingalready devoted

more

timetoMr. Hulst's opinions than theyjustify,^let

me

addthatanother_{year'sstudy of}

Yucca

fertilization has not only servedto confirmall that I have hitherto _written,but still

furthertoenhancethe importance^of

Pronuba

tothe plantand theintelli- gent nature of herunique performances. ^Prof.

Wm.

_Trelease,

who

has

made

the only other^carefulobservationson the_subjectwhich have

come

to

my

^notice,hasdemonstrated_(Bull. Torrey^Bot. Club,Aug., 1886, pp.135- 141) that the stigmatic liquor ^is not nectariferous, but that the _slight

amount

of nectar associated with the flowers is secreted in thin pockets formed by ^the partitions that separate the three ^cells of the _pistil,and which openexternallyby^acontracted porefrom whichthenectarispoured through ^a capillary tube (enclosed by the closely applied, but not out- wardlyunited, lobesof the ovary)^tothebase of the_pistil,sothat nectar- feeding^insects seekit not aboutthe stigma, but ^atthebase of the _pistil orof the _petal*,whether within or without. I have _fully verified Tre- lease's statementsby^dissectionand study of the ^insects seeking^thisscant nectar,and endorse his conclusion that while the observations serveto disprove any positive value of their nectar in the pollination of

Yucca

flowers, theyaddtotheimportance^of

Pronuba

_byshowing that theacts of collecting the pollenand transferring^itto the stigma ^are performed voluntarilyand without food compensation ^{as I}

was

at first inclined to believe.

Ihave_latelyhadthe pleasure ofstudying Yucca-whippleiⁱⁿ California and theremarkable_{tree-yucca (}Y. brevifolia) ⁱⁿtheMojave^desert.

The

former ispollinizedby

Pronuba

maculata_Riley,andthelatterby^a most remarkably^modified and adapted species which ^I _expect to describeas

Pronuba

_paradoxa.

Thus

_everywhereintheUnitedStateswhere

Yucca

_nominallyfruits

we

finditassociatedwithitsPronuba.

Iawaitwith interestand _curiosity

any new

discoveries in thisconnec- tion, but,so far as present knowledgejustifiesanticipation, ^Ishould ex- pect,whereneither

Pronuba

norPronuba-likeinsect exists, to findthe plant modifiedto

more

_{readilypermit}self-fertilization soonerthan to findApis mellifica the pollinizing agent, the opinion of Mr. E. L. Layard, ^of

New

Caledonia

(who

^firstexpressed^itin 1880; Nature, ^vol. xxii, p.606), andofMr. _Hulst, tothe contrary notwithstanding.

On

boardthe"City of

Rome," Aug.

^{22, 1887.}

155 Mr. Schwarz

said,

commenting ^on

^{Miiller'sstatementthatbees}

do

notvisit

white

_flowers, thatMiiller

was

not

speaking

^{of food} flowers atthe time,

but what he

calls

bee

flowers.

Mr. Howard _thought

thatProf. Riley's

experiments,

confining bees

with Yucca which

they did not touch,

were

conclusive.

Mr. Smith

said that the habits of

an

insect in

one

_localityare not necessarily the

same

asinanother.

Both Mr. Hulst and

Prof.

Cook had

seen bees

on Yucca. On _Long

Island

he had found Lachnosterna

in great

abundance on blackberry blossoms. Mr.

Townsend had found them

in

Michigan ^with

^{similar habits.}

He

had

^thisseason failed to find a _single

specimen on

the flowers

near Washington, though

^there

were

_{plenty of}beetles all

around.

Prof.

Riley

reasserted the similar fact

regarding

bees,

which were

often

very

capricious,

but showed

that,

where

_they

do

visit the

Yucca

flowers, they

have nothing

^to

do with

fertilizing

them,

and,

even

in artificial pollination

by man,

perfect ^fruit

can only be

obtained

when

the pollination^is

done

_{as fully}

and

carefully as it is

done by Pronuba.

Prof.

Riley

^{read the}

following paper

^:

Two

BRILLIANT

AND INTERESTING MICRO-LEPIDOPTERA NEW TO OUR FAUNA.

BYC. V RILEY.

I havehadfor

some

time, ^{as a}part of the material whichIhaveturned overto the National

Museum,

two^small

moths

of exceptional brilliancy and_beauty, whichare

new

to ourfaunaand whichItook occasiontostudy whilein

Europe

^lastautumn.

As

a rule,^Idonot caretopresent^isolated descriptions ofspecies, but in both these instances thereare special rea- sonsfordepartingfromthis rule, asthefirstisoneof the_largestand_pret-

tiestof the Tineina,havinga superficialTortricid habitus,and thesecond

isinteresting^asbelonging^{to asmall} group essentially exotic,which has been_placedby^authorsboth inthe TineidaeandtheTortricidae,and

which

virtually^is a

somewhat

interesting form belonging ^{rather to the} lower Noctuidee. I

name them

in

honor

of two of our most_capableand

most

worthymicro-lepidopterists,and ineachcase with permission.

SETIOSTOMA FERNALDELLA

^n. sp. Expanse, 12-13

mm.

General col- ors, vividpea-green, yellow,andmetallic bronze.

Head,

^vividpea-green, approachingⁱⁿ

some

instances to olivaceous; faceandpalpi paler,

more

yellowish.

Thorax

of the

same

vividgreen,

somewhat more

_yellowish on the borders, butespeciallyon thecollar,

which

^isseparatedfromthemeso- thoraxby^{a fineblacksuture.} Primaries of the

same

^vividgreen^{at basal} third,posteriorly limitedbya straight linewhich_slightlyobliquesoutwardly