Proceedings of the Biological Society of Washington.

VOL. _VII, PP. 81-104 MAY, ¹⁸⁹²

PROCEEDINGS

OF THK

BIOLOGICAL SOCIETY OF WASHINGTON.

SOME INTERRELATIONS OF PLANTS AND INSECTS*

r.Y C. V. RILE-Y, PH. D.

It is

my _purpose

to-night^to present

some

_phases^of the curi ousinterrelations

between

_plants

and

insects. In doing^{this I} shall not

have

timetodealwith the

remarkable

^series ofresults that

have

followed the

more

careful

and

accurate investigation ofthe so-called insectivorous orcarnivorous _plants,

and which have shown

thatthese plants arenot only possessed^ofthe

power

of

movement _depending upon

^nervestimuli, that

may ^be

^likened

in almost everyrespect tothe automatic

movements

^of_animals, butthat they actually possess digestive

powers and

_properties which, chemically

and

functionally, are the

same

as those

by which

animals digest their food. ^{It is}

my

^{desire rather tocall}

your

^{attentionto certain} phases ^ofplant fertilization

by

^insects.

*Thiscommunication was _presented for the most part extemporane

ously,with the aid of stereopticon views. In preparingit,byrequest,^for the_{printer, I}haveassumedthatthefactsalreadypublishedin reference toYuccapollination are familiar^tothe

members

of the_Society,andhave presented in the^briefestmanner _{such only}as throw _lightonthe _philo sophical portion of the ^article.

The

descriptive portion ^is condensed from amoreextended paperrecentlyprepared ^forthe Annual_Reportof the Missouri BotanicalGarden, but not yet published,and the illustra- trations are for the most _part borrowed in advance from that paper.

Figures8, 10, 11, 12,and_13,however,are from

my

previous publications^; Figure⁶ was preparedspeciallyfromthe stereopticon^slide; and_Figures

2, 3,and4arefrom theDepartmentof Agriculture and used bypermis sionof Assistant Secretary\Yillits.

11 KIOL.So.-.,WASH.,^Vol..VII,¹*!_'. (Si)

Miley Interrelations of

I

need

not tell the

members

of this Society that the old idea that flowers

were endowed

with

beauty and

_fragrance for our particular pleasure has

been

effectuallyset aside,

and

thatthese attributes

have come

to be looked

upon

in their true_light, as essential totheplant's existence

and

perpetuation; that,inother words, color,form, ^odor,secretions,

and

the general structure of flowers, ^all

have

reference to insects.

Nor need

I dilate

on

the

need

^ofcross-fertilizationin plants generally, orthe modification

which

insectpollinizers

have undergone

^{as a} consequence^ofthis need.

Some

ofthe

more

interesting ^facts are particularly well exemplified ⁱⁿ our _orchids, to the philosophic study ^of

which

Darwin's important

work

^"

On

theFertilization ofOrchids^"gave a distinct impulse.

But

here

we have

_adaptation ofthe plant only,and, with scarcely

an

_exception,

most

_{flowers, including} those of our _orchids,

may ^be

^fertilized

by

^{different insects.}

There

are, in_fact, few

which

are

dependent on

^asingle species for pollination, and, ^{so far as I}

know,

^our

Yuccas

furnish the only instance of this kind. It is to the fertilization of these plants that^I

would

first

draw your

^attention.

The Yuccas

are acharacteristic

American _group

of liliaceous plants, finding their

home more

particularly in the southern

United

^States

and

Mexico.

There

are

many

species

which have been

divided even into sub-genera

by

^Dr.

Engelmann,

^{as Sar-} coyucca, Clistoyucca,

Chenoyucca, and Hesperoyucca

^;

but

for our present

purpose

they

may

^all be included

under

the

one genus Yucca,

^{as they all} possess certain characteristics in

com mon,

viz,a_thick, sub-mucilaginous root,

which

^{is in} _reality a subterranean

stem

; lance-shaped, evergreen ^leaves,

narrow

or broad, rigid or _flaccid,

and

with the edges ^either filamentose, smooth, ^or

more

or less distinctly^serrate.

The

leaves

produce

acoarse _fiber, valuable for certain kinds of _fabrics, while the trunks of thetree

Yuccas have been

usedto

make

the toughest

kind

_{of paper.}

The

^{fruit of}

some

_species, as of _aloifolia

and

baccata, ^is fleshy

and

edible. It

is, however, the ^{flowers to}

which

I

would draw more

_especial attention.

They

^are pro

duced

in large panicles,

and

are characterized as arule

by

^the anthers not reaching

anywhere

near the stigma; sothatfertiliza tion

unaided

^{can take} _placeonly

by

^{the merest accident.}

The

Yuccas show

_great variation in _detail, both in _leaf, general habitus, flower-stalk, flower,

and

_fruit, from the

common

^sessile

Yucca jilaineiit<>* of our gardens ^{to the arboreal} forms, ^like

Structural Characteristics of Pronutxt.

83

brevtfoliaof the

Mohave

Desert

and

_fitifera of Mexico.

My

^re

marks

will be based_chiefly

on

Yuccafilamentosa,

which

isindig

enous

to the Southeastern States

and

iscultivated

beyond

^its natural _range,

under

a

number

of horticultural variety

names,

in our gardens.

An examination

ofthe flowerwill

show

at once the _peculiar

ities

which

I

have

alludedtoas characteristicofthe genus.

The stamens

or filaments arebent

away ^from

the stigma

and do

not reach

more than

two-thirdsthe length ^ofthe _pistil, the_stigmatic

opening

being ^atthe _tip of the prolonged style

and nowhere

within reach of the stamens, while the pollen ^either

remains

attached tothe

open and

withered anthers or falls in different sized*

lumps ^on

^{the underside of the} perianth. ^It

cannot

be introducedintothe _stigmatictube withoutartificialaid,

and

the plant

depends

absolutely

on

thelittlewhite

moth

_belongingto the Tineina

and known

as

Pronuba

yuccasdla Riley.

STRUCTURAL

CHARACTERISTICS OF

PRONUBA.

Upon

^asuperficial view, ^{this little}

moth shows

nothing very peculiar.

The

general coloration ^iswhite, the primaries being purely white

on

the

upper

^{surface; so that}

when

at rest in the half

open

^{flowers of the}

Yucca

^{it is} not easily detected.

The under

_{surfaces,however,}are

dusky and

offsetin _flightthewhite- eness of therestof the body, ^{so asto} render the _species

some what

difficult of detection while _flitting

from

_{plant to plant.}

The male shows no

_very

marked

peculiaritiesto distinguish

him from

the other

members

^ofthe_family,the

most

noticeable being, perhaps, the

prominence

^{of the}

exposed

parts of the _genitalia.

The

_{female,however,}

shows some remarkable

structural

pecu

liarities,

which admirably adapt

^{herforthe functionsshehasto} perform,^for she

must

fertilize the plant, since her larvaB feed

upon

^{its seeds.}

Now.

if I should ask

any

well-informed entomologist

what

arethe characteristics ofthe Lepidopterous

mouth,

^inthe

imago

state,

he would

unhesitatingly

answer

^:

The

lack of all

prehen

sileorgans

and

a coiled

tongue

capable ^of sucking liquids. If again ^I should ask

what

distinguishes the Lepidoptera from, say, the

Hymenoptera,

^inthe

methods

of ovi position,

he would answer

that the Lepidoptera lay eggs possessing, ^{it is} true,

an

infinite diversity of form, but usually attached externally to

some

_{part of}the food-plant^of the_species, while the

Hymenop-

Riley

tera as arule secrete _theirs,

and

are furnishedwith either a puncturing,boring, or

sawing

^{instrument forthat} purpose.

The

generalization

would

be_{entirelyjustified,}

though

^{there are}

many

curious exceptions ^{to it,} especially in the very

group

Tineina, to

which

our

Yucca moth

_belongs. It _is,however, necessary ^to

FIG.1. A,tipofanal jointandvaginal projection of Q ^Pronubayucca>eUa fromside, showing ovipositorwith partsextended;6,basal joint;c,its file-likesurface;d,ter minaljoint,withitsdorsal serratewing(/),^itsdentatetip(e),itsventral membranous

outlet_(.7),andtheextendedoviduct(/?); B,thesamepartsfarther enlarged; C,ventral viewoftipofabdomen, showing^{the two}pair ofrodsi,iand_k,k,withtheirmuscular attachments, the parts ofthe ovipositor similarly lettered as inA; M, m. eggs taken fromYucca_pistil;H,egg,showing development^ofembryon^;o,matureegg from ovary ofQ;r, s,genital claspers of cJ\^lateralanddorsalview-all enlarged.

state thesegeneral ^{truths in} order to

convey

a just idea of the exceptional nature ^ofthe

two

_organs to

which

Iwish

more

_par

ticularly ^to

draw your

^attention.

The

firstisa_{pair of}maxillary tentacles

which

are prehensile

and

_spinous

on

their

under

surface.

They

are peculiar^tothe genus

Pronuba and

existin

no

other

genus

Structural Characteristics of

Pronuba. 85

ofthe

many

^thousandsofbutterflies

and

moths.*

The

otherorgan

is the ovipositor,which, ^{instead of} being a simple opening, ^as typically

found

in Lepidoptera,^is here modifiedinto a

complex combination

oflance

and

saw. Ordinarily ^itis

withdrawn and

hidden, but

when

in action is projected ^far

beyond

^the tip of the

abdomen and

is then seen to consist of

two

principal parts the_{basal part} being imbricato-granulate ^Le.,

having

^adelicate

file-likestructure, the terminal _part being smooth,

but having

near the

end

a dorsal serrate chitinous

wing and

^astill

more

stronglytoothed corneous_tip.

The

internal structureisseento consist of

two

stout_rods, extending along the thin^{walls to} the verytip,

and

of a ventral canal orpassage-way^for thedelicate oviduct,

which

issilk-like

and

elastic

and may

be extruded ^for a_greatlength

from an

outlet near the

end

of the ovipositor.

This oviductis

smooth

_basally, but

armed

_along^its terminal third with retrorse hairs, increasing

somewhat

in

number and

strength

toward

the_tip,

around which

_theyare almost_spinous.

At

firstsight these

would seem

to be out_{of place}

and

to

impede

rather

than

^aid the insertionof such a delicatefilament_; but, as

we

shall presently see,the act of oviposition ^isa

most

intri cate

and

difficult

one and

these hairs aredoubtlesssensitive

and

tactile

and

serve thedouble

purpose

^ofenabling the

moth

tofeel

her

way

^{inthe ovariancell}

^and

^oftemporarilyanchoringⁱⁿthe softwall thereofwhile the egg ^isbeing passed ^toits destination.

Itwillbe seenthatthisovipositor^is

admirably adapted

^forcleav ing

through

^the

young

^fruit

and

then

running

the egg ^into the ovarian _{cavity, as}willbe presently described.

The manner

in

which

this ovipositor ^is

worked by

^{the four rods attached to}

strongmusclesisindicated _{at Fig.1,} C,the

two

inner rods

form

ing, as already indicated, the _rigid portion ^of the _ovipositor proper

and

theimbricate basal portion ^ofthe covering ^facilitat ing the invagination ^ofthe basal part

when

the _ovipositor is

withdrawn.

The two

outerrods are attached to strong

muscu

lar tissue in thewalls ofthe _vagina,

and when

the _ovipositor is

extended

toits

utmost

limitthis vaginalportion ^is partiallyex truded so as to appear ^{like a} basal subjoint.

More

detailed characterization of these parts ^is unnecessary^{in this} connection.

*Thereareover_12,000described_.speciesof Lepidoptera from Europe and_America,and those from other parts of theworld will double this number. Nearly^as

many

^moreremain, perhaps, ^tobedescribed.

Riley Interrelations of

THE ACTS

OF

POLLINATION AND

OVIPOSITION.

Having

^thus

drawn

attentionto the

most

characteristic struct ures of

Pronuba, we

shallbetter

understand

the_followingaccount oftheactsof pollination

and

oviposition

which

I quote

from an

articlerecently prepared^forthe

Annual

_Reportof the Missouri Botanic

Garden

:

"

Though

^{all theacts ofthe female are}

nocturnal,^{it is}notatalldifficult tofollow

them

with a_lantern,for, albeit ordinarily shy,she

may

^be closely

approached when about

to oviposit.

Her

_{activity begins} soonafterdark,butconsists, at first,in as siduouslycollectingaload_{of pollen.}

She

may

^{be seen}

running up

^tothe top ^of

one

ofthe

stamens and _bending

her

head down

over theanther, stretching the maxillary tentacles, so wonderfully modified ^forthe purpose,^{totheirfullest} extent, the tongue uncoiled

and

_reaching totheopposite side ofthe stamen.

In

this

manner

sheisable to obtain afirm hold ofthe stamen, while the

head

iskept ^{close to} the anther

and moved

_peculiarly

back and

_forth,

some

thing^{as in} the

motion

ofthe

head

of a caterpillar

when

_feeding.

The

_maxillary

palpi are

used

inthisactvery

much

asthe ordinary

mandibles

are

used

in other in sects,

removing

^orscraping thepollen

from

pollen" the anthers

toward

the tentacles. After thus gathering the pollen she raises her

head and commences

to

shape

^{it into a little}

mass

or_pellet

by

using her ^frontlegsvery

much

as acatdoes

when

_cleansingher

mouth, sometimes

using only

one

_leg, at another time _both,

smoothing and

pressing thegathered pollen,thetentacles

mean

while _stretching

and

_curving. After collecting ^all the _pollen

from one

anther she proceeds ^to another

and

_{repeats the opera}

tion,then toathird

and

_fourth,afterwhich, with her relatively largeload often thrice as large asthe

head

heldfirmly against the neck

and

front trochanters,she usually runs

about

orfliesto another plant; for I

have

often noticed that oviposition, as a

FIG. 2. Female yuccasella gathering Xo,

Pollination

and

Oviposition.

87

rule,^is accomplished ⁱⁿ

some

otherflower

than

that

from which

the pollen

was

_gathered,

and

that cross-fertilization is thusse cured.

"

Once

_fully

equipped

^{with this}

important commodity,

^she

may

^beseen either crawling over or resting within the _flower, generallywith the

head toward

the base.

From

timeto

time

she

makes

a

sudden

dart

and

_deftly runs

around

the stamens,

and anon

takes a_positionwith the

body ^between and

the _legs straddling

two

of

them,

^her

head

being usually turned

toward

the_stigma.

As

the terminal portion^of the

stamens

is

always more

orlessrecurved,she _generallyhas to retreat

between two

of

them

untilthe _tip of her

abdomen

can reach the _pistil.

As

.FIG.3. Flowerof Yuccafilamentosawith near_petals removed, showing Pronubain act of ovipositing.

soon as a favorable point ^is reached, generally just

below

.the middle, she ^restsmotionlessfor ashort time,

when

the

abdomen

is slightlyraised

and

the lance-like ovipositor^is thrust into the soft tissue, held therethebest part of a minute, while the egg^is

conducted

toits destination,

and

then

withdrawn by

^{a series of}

up-and-down

^motions.

"

In non-technicallanguage, thepistil orthe

young

fruit, be low thestigmatic tube,

shows

_externally at this time six quite distinctlongitudinaldivisions,each

having

^a

median

_ridge,there being ^six corresponding depressions or concavities in

which

the six stamens _{fit, especially} atthebase. Technically,the_pistil is

a tlim>r<.'ll'd ovary, the styles bifid at tip

and

united so as to

Riley Interrelations of

form

the stigmatic tube.

A

transverse section

anywhere about

the

middle

will

show

that each of thesix longitudinal sections contains a

row

of ovules within

an

ovarian cell.

More

_strictly, the ovulesare in_pairs, as there are but three

primary

^sections or_carpels, divided

by

^three

primary

^divisions or dissepiments.

Figure 4

shows

a transverse section of

one

of these

primary

divisions or carpels

which

well indicatestheposition ofthe ovules

(a),the funiculus _(6),the placenta (c),

and

the ovariancell (d).

As

the fruitenlarges, the three secondary dissepiments

narrow and

_coalesce,while the other three widen, ^{so that}the

pod

^be

comes

practically three-lobed

and

the seeds are

more

_distinctly

FIG.4. Transversesection ofoneofthe _{carpels of}Yuccapistil^: a,ovule;b,funicu- lu$; c,placenta; d,ovariancell; e,fihro-vascular bundles;/, fibro-vascular tissue: </

primary dissepimentX^9.

in _pairs,theinnerside straight

and

the external quite convex.

In

ovipositionthe

young

^fruitis pierced justwithin theridge¹ in the depression occupied

by

the stamens,

and

almost always

on

the side of one of the

primary

^or deeper divisions,

where

the walls are thinnest, so thatthe ovipositor enters the ovariancell attheexternal or

rounded

side of

an

ovule

and

does not ordi narilytouch the ovule itself. Rarely, however, the ovipositor penetrates the _ridge

and

_passes

between two

^of the _{ovules, or}

sometimes

even _penetrates one, this last case being, however, quite exceptional.

"

The

_egg ^is

an

_extremely delicatethread-like _structure, aver aging ^1.-")

mm.

ⁱⁿ length

and

less than 0.1

mm.

_{(Fig. 1,} /., n, o)

Opposition ^of

Pronuba. 89

in diameter, tapering^atthe base

and

_{enlarging slightly}

toward

the capitate end.

which

has also a_slightly indurated _point. It isimpossible^tofollow7itwith the

unaided

_eye'or in factwith

an

ordinaiTlens,even^ifthe _pistilbeatonce

plucked and

^dissected;

but

by means

^{of careful} microscopic ^sections

we may

^traceits

course.

From

the _position

assumed by

^the

^moth,

^theovipositor punctures thepistil

somewhat

_obliquely,

but

as the egg^is

much

longerthan thediameter ofthe ovarian cell,thedelicateoviduct ofthe

moth bends and

then runs _verticallyalong the inner part of the cell next the _placenta,

and

leaves the egg extendingⁱⁿ this longitudinal direction along

some

sevenor eight ovules, as

shown

in theillustrations (Fig. 5, r, c).

The

_apical

end

of the

FK;.5. a,longitudinal section ofpistilofYuccafilamentosa,showing(b, b)punctures ofPronuba,and_(c,c)thenormalposition ofher eggsⁱⁿtheovariancell;d,section of a puncturedcarpel7daysafter oviposition,showing^theeggyetnnhatchedandtheman nerinwhichtheovulesin tin¹neighborhoodofpuncture havebeenarrestedindevelop mentso astocause^Ilieconst rietion: e.section ofan older_carpel,showing^{the larvaabove} the originalpuncture^;/,aseed1:5days fromoviposition,showing young^larvaatfunic ularbase enlargements^indicated.

egg soon enlarges (Fig. ^1. ??,),

and

the

embryo may

^{be seen de}

veloping^{in it} very

much

as inthe case ofthesimilarly elongate

(>o-o'sof_gall-flies(Gynipidae),

though

^thepediceldoesnot_shorten, as observed in these last.

Segmentation

^{is noticeable}

on

the second _day,

and

the

Yucca

ovule at once begins ^toswell

and

enlarge, the irritation (doubtless mechanical) influencing the plant^tissue

much

asin the case ofthe punctures^ofthe irall-flies

12 BIOL.Soc.,WASH.,VOL. VII,IS'i-J.

Riley Interrelations of

justmentioned.

Sometimes two

or

more

_adjacent ovules are thus affected."

It

may

^{be well righthere to look a little}

^more

closely into the

minuter

characteristics of the

Yucca

flower at this stage of its

development

^that

we may ^{understand more}

fully the action

and

influence of the

moth. In my

first article, published

some twenty

years ago,

announcing

^the discovery^of

Pronuba and

its action

on Yucca

pollination, ^I

was

strongly inclined^tothe idea thatthe act of pollination

had some compensating inducement

tothe

moth,

^aside

from

the impelling^instinctofperpetuation^of the _species.

At

that time it

was supposed

^thatthe stigmatic liquor

was

nectarian,

and

the conclusion

was

justifiable thatthe

moth,

^{attracted to it for} feeding purposes,

would

incidentally inducepollination.

On

thisviewofthe matter itdid not_require a_greatstretch of the imagination ^to conceive that the pollen

might

also incidentally

accumulate

in the _spines,

and

that the vigorous ^{action of} the

head

that

had been

noticed

might

^even

be

considered^as

an

effort to get ^rid of the

encumbrance

while feeding.

In

_{those days} I

was more imbued

with the

common

notion that lower creatures areimpelled ^forthe

most

_part

un

consciously^{to theiracts.}

Twenty

years ofstudy

and

_experience

have

only served^toprove the^actsof

Pronuba

the

more

unselfish

and

without food inducement.

A

longitudinal section of the

upper

portion ^of the _pistil will

show

the _stylewith the _stig matic tube,

which

at this time

communicates

with the ovarian

cells.

Now,

^Treleasehas

shown

that thestigmatic liquor^is not nectarian,butthat the_slight

amount

of nectar associated with the flower^issecreted in pockets

formed by

^the partitions that separatethethree cellsof the_pistil,

and which open

externally near the _style

by

a contracted pore

from which

the nectar is

poured through

a capillary tubetothe base ofthe _pistil.

The accompanying

illustration (Fig. 6)renders this

more

intelligible,

a,being a longitudinal section

through

^{the center of a} pistil,

showing

^the septal gland (#), the duct _(cZ),

and

the outlet at base; ft, a cross-section ofthe_pistil

about

the middle,^also

show

ingthe duct(VI)

and

_{gland (#);} c.a

more

_enlargedcross-section of thenectar apparatus^{; e}

showing more

_fullythe structure of theseptal gland, while kis a longitudinal section of the top ^of the_pistil,

through

^the lobes,

showing how

the_stigmatic tube _(*) connects with the ovariancell (o _c), o being the ovary,./' the fu- niculus,p the placenta,

and/r

fibro-vasculartissue.

r

Apparatus

of Yucca. 91

These

interesting facts,

which

^I

have

fully verified,

show

that nectar-feeding ^insects seek it not about the _stigma, but atthe baseof the

stamens

orofthe _petals,

whether

within orwithout.

In

_short, the nectar in these

Yucca

flowers has

no

value inpol lination,

and _Pronuba,

in collectingthe _pollen

and

transferring

ittothe stigma, finds

no

food compensation, a conclusion

which

is confirmed

by

^a study ^ofthe

minute

structure

and

internal

Fia.G Nectar apparatus^ofYucca: a,longitudinal section ofpistil,withduct(d)and gland (g); 6,cross-section about middle,showing sameparts; c, still more enlarged cross-section ofnectar apparatus;e,structure_{of septal}gland ^afterTrelease;h,longi tudinal section of top ofpistil,showingstigmatic tube() ovarian cell_(cc),ovule(o),

funiculus_(/),placenta(p),andfibro-vascular tissue_(/(-)

anatomy

^ofthe

moth, which

^{indicate that} the tongue proper,

though

strongly developed, has^{to a.}great extent,^ifnot_entirely, lost its function as a sucking organ,

and

that the alimentary canal is practically functionless, being aborted ^before reaching the anus. This defunctionization, jf^I

may

^use the term, ^ofim-

Riley Interrelations of

portant ^structureshas not proceeded ^{so farin} Pronuba_yuccmella as in P. metadata,

which

_pollinizes Yucca _whipplei.

Those

not familiarwith the structure ofLepidoptera^willhardly appreciate the modificationsto

which

I shall allude, however, without the preliminary statement ^thatthe tongue ⁱⁿ Lepidoptera ^consists of

two

distinct parts (maxilke)

which

are

more

^orlessconcave

on

their innerside

and

united atthe bordersofthe concave por tion

by

^certain lockingarrangements ^to

form between them

the sucking^tube.

Now,

^{while in}

^most

^{cases the}

^two

parts

may

^be

relaxed

and

_separated

by

force,innature they^areneverso sepa rated,while the_tip of the tongue ^is

more

orless

acuminate and

the

two

_{parts here very} firmly united.

FIG.7. PKONUBAMACULATA: ,tipof femaleabdomen;bjo,basal joint of ovipositor:

tjo,terminaljoint of ovipositor;ov,oviduct;

m

_p,max.palpus;

m

t,maxillary^tenta cle; t,tongue;gs,claspers of male from side; gp, claspers ofmale frombehind en- largernant indicated;pr, frontwings,showing arrangementof spots intwoofthemore commonforms,hair-linesshowing^naturalsize.

In Pronuba

_yuccasellaI

had

often noticed that the

two

_parts

became

_separated

and

in fact were almost always separated

toward

the_tip, thus suggesting a ^loss of functionas a sucking organ,

but

otherwise the tongue ^is stronglydeveloped, and, with the exception ^ofthe

weakness

of the locking arrangement, not particularlyabnormal. In

Pronuba

_maculata,

however

_{(Fig. 7),} the

two

_{parts ofthe tongue} arebut veryfeebly united,

and

often

more

or less disconnected,

and

are actually thicklycovered with

minute

hairs

and more

_sparselywith longer spinoushairs,inter

mixed

; they^arealsoswollen

and

_enlarged

toward

thebase.

The

import

^{ofthis fact can bestl>e}

conveyed

^to

you by

^thestatement

Development and

Traiisformations of

Pronuba, 93

that inall other Lepidoptera ^{that I}

know

of the tongue ^is a

smooth

_organ

and

in

no way ^armed,

except near the tip. In short, the tongueⁱⁿ

Promtba

maculata has

become an

_accessory

tentacle, serving

and

_helping in pollination, but probably ⁱⁿ capable^ofusefor feeding purposes.

These

structural peculiari tiesjustifythe conclusion,

which

observationconfirms, that Pro-

nuba

does notfeed in the

imago

^state.

In

other words, she has

no

incentive to go ^to the stigma with her load of pollen other

than

^{that of}pollinizing,

and

the _slight

amount

of nectar

which

the plant ^secretesiswell calculated to lead other insects

which

seek it

away ^from

the stigma

and

thus nottointerfere withPro- nuba's mission.

DEVELOPMENT AND TRANSFORMATIONS

OF

PRONUBA.

On

thissubject^I

need

_only

remark

that theaction of oviposi- tioncauses adisorganization ofthe plant^{tissue in}the

immediate neighborhood

^of the apical portion ^ofthe egg

and

the _swelling ofthe adjacent ovules; thatthe

embryo

developsⁱⁿthe_capitate

end

of the _egg,

and

while the larva is white at _first, or of the exact color of the

young

ovule,^it

becomes

_{slightlygreenish} or roseate

when

full grown,

which

is in

about

a

month,

^orcoincident with the ripening ^of the seed. It perforates the capsule

and

_drops to the ground,

having

^{six thoracic legs,}

which

doubtless aid it at this period ^{of itslife. It} remains

through

^{the fall, winter,}

and

_early

spring

months

in a

tough

cocoon, transforms to the _chrysalis state

about

a

week

beforethe

Yuccas bloom

_again,

and

_finally issues as a

moth

to continue the

annual

_{cycle of}itscareer. Fi . s. PKONUBA

The

_{chrysalis (Fig.} 8), has a capitate spine

and

aseriesof dorsal spines,

some

of

which

are

spatulate

and _admirably

fitted for helping ^{it to}

work _through

the ground.

"

The

effect ofthe puncture^ofthefemale

moth on

the fruitis at once noticeable

by

^a darker green discoloration externally.

In

timethis

becomes

a depression,causing aconstriction of the pod,

and

theirregularities of the

pod

(Fig. 9, 6, c),

which have

been supposed

^tobe characteristicofthe

genus

Yucca,are really

due

tothese punctures,

which

_ordinarily occur _just

below

the middle."

The

absolute

need

of

Pronuba

inthepollination ofour deniscent

Yuccas

I

have proved

^over

and

over _{again, in}

many

;?/ Interrelations of

ways.

The

plant never produces seed

where Pronuba

does not exist

; it never produces seed

when

sheis

excluded

artificially,

and

experiments

which

I

have made

with artificial or

brush

pollination ^all

show

that it is

much more

^difficult to ensure complete fructification

than would

atfirst appear,

and

that the act of pollination^is rarely

performed

^{with a}

brush

or

by

using the flower's

own

_filaments, as successfully as ^itis

done by

^Pro nuba. It is

Pronuba

_yuccasella

which

_pollinizes all our

Yuccas

eastof the

Rocky

^{Mountains, sofar as}

known, ^and

^the species

is

remarkably uniform

in character,^its

appearance

ⁱⁿtime being coetaneous with the _flowering of Yucca filamentosa.

On

the western _plains its

appearance

^has

become _adapted

totheflower-

FKJ.!). Mature _podsof Yucca angustifoiia: a, artificially pollinized and _protected fromPronuba; 6,normal_pod,showingconstrictions resultingfrom Pronuba_puncture andexitholes_{of larva;c,}oneofthelobescut open,showinglarva within.

ing of Yuccaangustifoiia, butin the _east,

where

these

two

_species of

Yucca

are frequently

grown

^side

by

side, ^Y.angustifoiiaflowers

two

or three

weeks

earlier than Y.filamentosa

and

generally too early to receive thevisits of

Pronuba,

^{so that it} produces seed only

on

_very rare occasions. Yucca _brevifolia is pollinized

by

r/'on/ihti

synthetica Riley, the

most remarkable

_species of the genus,

having

very^stout maxillarytentacles, a very^{stout ovi} positor, shorter

than

that ofyuccasella, butcharacterized chiefly

by having

fuliginous

and

unsealed

wings and

a_polished,

naked

and

flattened

body

^{structures allwell}

adapted

^forcrawling be

tween and

about the

compact and crowded

flowers, with their

Pollination of other Species of Yucca.

95

thick

and

_{leatherypetals,but very}

abnormal

inthe Lepidoptera.

In _fact,thisspecies strongly ^recalls inits generalaspect

some

^of the saw-flies belonging ^to the

genus

Dolorus, the resemblance being heightened

by

^{the rather} conspicuous, cenchri-like _spots,

and by

the conspicuous ^division

between

thorax

and abdomen.

Italsostrikingly^recalls

some

ofthe Neuroptera,^asSiall-sinfumata.

Now

these resemblancesto insects of different Orders

and

to families

which

are generally

conceded

to be of

low

type within their Order,

cannot

_possibly

be

_mimetic,as there can be

no con

ceivable cause,purpose,^or

advantage

ⁱⁿthe mimicry. ^{Itis also} impossible^to accountfor these resemblances

upon any

present genetic connection.

Yet we

^are _{hardlyjustified} ⁱⁿ _disposing ^of

them

as

merely

^accidental

and

without

meaning. They

suggest a_possiblesynthesism ⁱⁿthe _past,

when

_types

were

^less _special ized

and

present Orders

had

not

become

sowell differentiated.

Yucca_whipplei,

which

occursinsouthernCalifornia,hasflowers distinguished

by

^their relatively long

and

stout stamens, the pollen of

which

is copious

and

_glutinous,notto say

mucilag

inous,

and

a _short,contracted _style, with the _stigma, however,

expanded and

covered withsticky threads. ^{It is} pollinized

by Pronuba

maculata _Riley,which, ^asalready

shown,

^{has a}

tongue

modified into

an

_accessory pollen-gathering organ. If

any

species of

Yucca would seem

notto need aspecial insect^for pol lination, Yucca_whippleiisthat species; forthe long stamens, the sticky

and abundant

_pollen,

and

the_peltate,hairy stigma

would

all

seem

to facilitate ordinary pollination. Nevertheless, the very^restricted style

would seem

to be purposely developed ^to counteract these other facilities,

and we

find a

Pronuba

asso ciated with _it, with a

remarkably

modified tongue,

and

with the maxillary ^tentacles very long

and

attenuated atthe _tip struct ures

which

doubtlessenable the

moth

to perform theact of pol lination. I

have

never

been

able toobserve the_act,nor has

any one

_yetrecorded either the acts of pollination or oviposition.

There

will be nothing peculiar

about

the _latter, but I shall

be

very gladto get actual experience in reference tothe _{former, as} I

am

satisfied thatthe observedfacts willshow, ^still

more

_fully

than

in the case of

Pronuba

yuccasella,thatthe _special modifica tions of both flower

and

insect

have gone on

^untilthe

mutual

interdependence has

become

absolute.

There

is

much

_yettolearn of thepollination of other_species of Yucca,

and

I-

am

particularlyanxious toobtain the insects

which

willdoubtless be

found

associated with them.

The

_regal

Riley Interrelations of

tree

Yucca,

^Yucca filifera, of northeastern Mexico, reaching ^a height^of fifty feet, with its

pendulous

panicles ^five or six feet long,has a veryelongate pistil

and

comparatively^shortstamens.

The

few-

pods which

^I

have been

ableto

examine

indicate the presence ^ofa

Pronuba and

doubtless of adistinctspecies

which

will prove veryinteresting. Yucca _baccata, Y.trmilirnirn,

and

all

the_species

which

aresufficientlydistinctive in characters

and

in range,

may

be expected^to

have

_special

Pronubas

associated with them.

THE BOGUS YUCCA MOTH.

An

interesting ^factconnected with

Pronuba and Yucca

_polli nation isthat there is always ^associated with

Pronuba

_yuccasdla another

moth, which

^{bearssuch a}

remarkable

superficial

resem

blanceto _it,

though

possessing

no power

of pollination, that ^it

has caused

much

confusion in the past on the_{part of}carelessobservers

and

led to a

good

^{deal of misstate*-}

ment and

error. Thisis

what

I

have

called the

Bogus Yucca Moth.

Pro-

<1o.ws

dedpiem

(Fig. 10). In size it is

somewhat

smaller,

on

the average,

than

Pronuba, and, while

found

as sociatedwith_it,appears^{ratherearlier.}

The

female has

no

_maxillarytentacle,

but

otherwise the

genus

^{has all the}characteristics

which would

place ^it in the

same

_family as Pronuba.

The

_ovipositor ^{is a}

strongerinstrument_(Fig.

11),but structurally

ho

mologous.

The

_{eggs are}

thrust intothe

stem

while yettender_; they^areelon gate in form, but ^short

and rounded

at both ends,resembling the

un

developed

ova

ⁱⁿthe

ova

ries of

Pronuba. The

larva is absolutely apo-

*2gffi%* ^-

doUS

_{(Fig. 12,0)j}formsits parent;h,basal joint of ovipositor;c,itssculpture

cocoons within the _stem, ^{'' t('nilill;l1.'oint "fSiin'"'its (i'' Inor<1 enlar*ed:>}

Fir,. 10. PRODOXUS DECIPIENS: a,

imago, wings closed^{; b,}female im ago,wingsexpanded natural size;

c, enlarged maxillary palpus with

itsbasal tubercle.

and

transforms^{the ensu-}

<

srenitaliaofO ^fr

ensiiinti' year ^{to a chrysalis,}

which

has a

much

stronger capitate

Tlie

Bogus Yucca

^Moths.

97

spine, but the barest trace of dorsal spines

on

the

abdominal

joints. Itissues partly

from

the

stem

_{in giving} out the

moth.

As

I

have

elsewhere

remarked

:

"

Who,

studying^these

two

_species in alltheir characters

and

bearing, can failto concludethat, notwithstanding the ^essential differences that distinguish

them

_{not only} specifically,but _ge- nerieally,they^arederived

from one and

the

same

ancestral

form

?

Pronuba,

depending

^{foritsexistence}

upon

the pollination ofthe flower, ^is profoundly modified ⁱⁿ the female sex in adaptation tothe _peculiarfunction of pollination. Prodoxus, dwelling ⁱⁿ the flesh ofthefruit or in the flower-stem

and

_{only indirectly}

Frr;.VI. PnonoxrsDKCFIMKXS^: a,larva; b,headfrom above;c,d, leftjawandantenna; e,pupa:/,infestedstem nut open ^to show the burrows, castings,coeoons, and pupa shell(/j)-allenlarged butf,thehair-linobetweennandcshowingnatural length.

depending upon

^thefructificationofthe plant,^isnot so modified, but has the ordinary characters ofthe familyⁱⁿ bothsexes.

In

the former the larva quits the _capsules

and burrows

ⁱⁿ the

ground

; it has _legs to aid in its work, while the chrysalis ^is likewise beautifully modified to

adapt

^itto prying

through

^the

ground and mounting

^{to the surface.}

The

_latter,

on

the con trary neverquitting the

stem

_has^

no

legs in the larva state?

and

in the_chrysalis state is

more

particularly adapted,

by

^the

Hoc., WASH., VMT.. VII,^LSft

Riley Interrelations of

prominence

^{of the}capital projection, ^topiercing the slight cov ering of the

stem

left

ungnawed by

^{the larva.}

The

former is

veryregular in^its

appearance

^{as a}

moth

at the timeoftheflow ering of the

Yuccas

in their native range.

The

latter appears earlier,as the food ofits larva isearlier ready,

and

the female could notoviposit in the_riperstem."

Some

ten _{species of}this

genus Prodoxus have been

^described,

all of

them _having

_{the very}

same

structural characteristics

and

in the adolescent states being scarcely distinguishable. Pro- doxus _decipiens is associated with

Pronuba

yiiccasellaeast of the

Rocky

^Mountains,

^and

^Pro-

do.i'ii* sordidiis is similarly as sociated with

Pronuba

_synthe-

tica, breeding ⁱⁿ the flower sterns of Yucca brevifolia. All the otherspecies are associated with Pronuba, maculata,breed ing ^{either in} the base of the capsules or inthe flower

stem

or the

main stem

^of Yucca whipplei. ^I

have found

Pro

doxus

larvaein the stemsofallother

Yuccas which

I

have been

able to

examine, and

^{doubtless a}

number

of other species are yet ^to be discovered

and

characterized.

The

_species so far

known

are interesting in that they ^{illustrate in}a

remarkable manner what

I

have

called fortuitous varia tion,or superficial^color- ationalcharacters_; also a

great tendency

^to graduate^intoeachother

b y

^variations

among

themselves, not onlyⁱⁿ thestructure ofthe ovi positor

and

the

male

genitaliabutinthe

wing

markings.

The

time to

which

these

remarks

are

limited will prevent

my

going ^into descriptive ^details, and

FIG.13. PRODOXVS MARGIXATUS^: a,analab dominal_{joint of}female X26;^bjo,basal joint of ovipositor; tjo,terminal_{joint do.;}

ov,oviduct; c,claspers ofmalefrom above

X18; pr, front wing ^hair-line showing naturalsize.

FIG.14. PRODOXVS Y-IXVKIH hair-line,underneath shouii taliaofmale,dorsal view

X18; d,anal joint of ^t'em sorted,lateral view X^20:

furtherenlarged.

i, left front vring, natural sixe: li,geni- 14

; c,do., lateralview

B with ovipositor ex- tip of ovipositor ^still

Caprijication of the Fig.

99

FIG.15. Puonoxrs nti,i>ii.vi>KNSis: a, left

I content myself with illustrating in this connection a few of the

more

_distinctly

marked

_{species, Figs.} 13, 14, 15,

and

16.

The _genus

interests us most, however, in indicating

how

^Pro

nuba

with all her abnormal,

peculiarities,has

been

evolved_; for

though we have

_striking differences in habit

and mode

ofdevelopment,^oflarva,pupa,

and

_imago,

between Pronuba and

_Prodoxus,yettheaffinities are equally striking,

and

the

two

genera exemplifyⁱⁿ

an

ex-

/ front wing, hair-line underneath showing

CeptlOlial degree the

power

^Of natural size;6,male genitalia, dorsal view

natural selection to intensify

" x¹⁵;c'do-<lateralview- x^is.

habits

and

structures in opposing ^directions according ^to the requirements ^{of the}species.

Prodoxus

is practically

dependent upon

^{Pronuba, forifthelatter}

did not _fructifythe _plant, the former

would have

in time

no

flower stems to breed in,

and

while

Prodoxus

has

gone

^on,

ya

^

^ma~-

^ generation

after

_generation

V

with

comparatively

little

FI,; . i<i.-pKODoxus RETICUI..VTUS: Female change,

Pronuba

has

become

with wings expanded ^hair-line showing profouildlv Specialized ^{tofit it} for a

more

_{specific purpose.}

CAPRIFICATION OF

THE

FIG.

It

was my

^{intention here to} explain ^to

you some

interesting factsas tothe caprification ofthe _fig

and

the

remarkable

struct ural peculiarities

and

influence of the caprifig insects. It _is, however,^a

somewhat

complicatedsubject,

and

Icould not within thetimeallotted

me do

_justicebothtoit

and

thematterof

Yucca

pollination.

As an

indication, however, ^of

how

_profoundly

modified in this particular case the plant

and

the insect

have become

in their

mutual

adaptation, ^I

may

^statethat the perfect

Smyrna

fig, the

most

esteemed ofthe edible_species, can be pro

duced

_only

by

^the intervention of the Blastophaga psenes,

and

that Dr. D. D.

Cunningham

^has recently

shown,

^{in the}

Annals

ofthe

Royal

^Botanical

Gardens

of Calcutta, ^vol. I,

Appendix

L, 1889,

by

repeated

examination

^$ of the fruit of Flcusroxbtirghii, that pollination, inthe ordinary

meauin^

of that term,^is,inthat

Riley of

particular case,out of the question,

and

that the

development

of the seed in this species^is exclusively

due

tothe stimulation ofthetissues caused

by

the puncturing ^of the Blastophagas; in other words, that these insects actually represent the

male

ele

ment

in the fertilization. This is certainly the

most

extraordi

nary phenomenon

^inthehistory offertilization,

and

ifconfirmed

and

Dr.

Cunningham ^{has been most}

^careful

^and

circumspect ⁱⁿ his

work

itwillgive a

more

striking instance

than any we have

hitherto obtained of the

mutual

interdependence

which

_plants

and

insects

may

^attain

^and

^thesurprising

manner

in

which

_they

may modify

^{each other.}

GENERALIZATION.

The

peculiarities

which

I

have endeavored

to present ^to

you

arefull of suggestion, particularly^forthose

who

are in thehabit of looking

beyond

^the

^mere

^{facts of} observation in endeavors to find

some

rational explanation^of

them

;

who,

^{in otherwords,} see in everything they observe significances

and harmonies

not generallyunderstood.

The

^factsindicate_clearly,it

seems

to

me, how

the peculiar structures of the female

Pronuba have been

evolved

by

gradual adaptation ^tothe particular functions

which we now

^findher performing.

With

the

growing

adaptation ^to Pronuba's _help,the

Yucca

flowerhas _lost, toa great extent,the activity of^its septa!glands^; yet coincidentwith it

we

find

an

in crease in the secreting

power

^ofthestigma. This increase ofthe stigmatic fluidhas

undoubtedly had much

to

do

with _originally attracting the

moth

_thereto,while the pollinizing instinct

doubt

less

became more and more

fixed inproportion ^astheinsectlost the

power

or desire of feeding.

With

the mind's eye ^I

can

look

back

intothe past

and

_picturethe gradualsteps

by ^which

^thePro- doxids to

which

I

have

alluded

have

differentiated along^lines

which have

resulted in their presentcharacteristics.

On

the

one

side I see variations

which have become

sufficiently fixed to be considered_{specific; yet}

which

can

have no

_{especialbearing}

on

the

life necessities of the _species, but are a

consequence

^{rather of} that universal

tendency

^{tovariation with}

which

every student of

Nature becomes

profoundly impressed.

Thus

the

wing-mark

ings vary

from

a darkergeneral coloring,^{as in} Prodnsuxxiiest'en.x, to a

more uniform

intermixture of the black scales

among

^the

white,^asin_cinereus, ora sparserintermixture_thereof,as in_pulver- nlentus.

The

disposition oftheblack scales isin spots orbands,

whether

transverse or longitudinal, ^as in marginalus,reticulatus,