Figs

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FIGS

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AUG 16 1922

FIELD MUSEUM OF NATURAL HISTORY

CHICAGO
1922

580

FH5l
no. 1-10

m is 1922

5UTS5A4

58-
noJ-IQ

Field Museum of Natural History

DEPARTMENT OF BOTANY
Chicago. 1922

Leaflet Number 1

Fig:

"The wild figs upon the fig trees contain a creature
called psen : this is at first a little worm, and afterwards
having ruptured the case the psen flies out. and leaves it
behind. It then pierces the unripe figs, and causes them
not to fall off. wherefore gardeners place wild fruit near
rhe cultivated kinds, and plant the wild and cultivated
plants near each other." — Arisrotle. History of Animals.
B. V.. Ch. XXVI 3.

Botanically the figs are a subdivision of the mul-
berry family. They are peculiar in not having their
flowers exposed, like most flowering plants, but con-
cealed within a hollow, urn-shaped receptacle which
has precisely the appearance of a young fruit. The
apparent absence of flowers is often a matter for com-
ment. An old Chinese writer on Materia Medica and
Natural History in discussing the fig calls it the "fruit
without flower." In reality the flowers are numerous
but insignificant in size and in appearance. All other
members of the family to which the figs belong have,
like the mulberry, the flowers and the individual fruits
on the outside.

Some 600 species of wild figs have been described
to date. A few of them are cultivated or well-known
plants, such as the rubber plant which in its normal
habitat is a rubber yielding tree, the Banyan tree which
with its numerous proproots may spread over an acre
or more of ground, and the sycamore fig that furnished
the everlasting wood for the coffins of the Pharaohs.
The vast majority of figs, however, grow in semi-tropi-
cal and tropical forests and jungles as shrubs, trees, or

2 Field Museum of Natural History

even as vines. Two species grow native in the sub-
tropical, southern part of Florida. One of them is a
so-called "strangling fig." These begin their lives as
parasites on other trees, growing at first much like
the mistletoe, but eventually sending their own roots
to the ground.

The cultivated fig (Ficus carica) is a native of
Semitic Asia, perhaps particularly of southern Arabia,
but occurs also in Syria and in Palestine. Smyrna
was as famous for its figs in ancient times as it is now.
From western Asia the Phoenicians and later the Arabs
carried the fig throughout the entire Mediterranean
region. The old Greeks scoffed at the barbarians who
did not have figs and wine. Romulus and Remus, ac-
cording to tradition, were suckled by a she-wolf under
a fig tree. In ancient lore the fig occupied a place such
as does our more familiar apple tree of the Garden of
Eden. Before the appearance of man, figs grew in
Europe and in North America. Leaves and fruits like
those of the cultivated fig have been found fossil in
France. With the Glacial Period the fig of course dis-
appeared from the modern temperate zone those
which now grow in Europe were all introduced horti-
culturally. Figs have long been grown in China, hav-
ing been brought by way of Persia from Asia Minor.
In modern times the cultivated fig has been introduced
into many lands. It is grown in South and Southwest
Africa, in South America, and in Australia. It has
been grown in Sussex in England. It is successfully
cultivated in the United States, especially in California
and in the Gulf Region, particularly in Texas. In
African Sudan where the fig has failed to grow on its
< iwn roots, it has been grown budded on the more trop-
ical sycamore fig.

The cultivated fig is ordinarily a rapidly growing
small tree with palmately lobed leaves and with a soft

[2]

Figs 3

wood. It lives sometimes to a great age and then
reaches large dimensions. It may be uncommonly pro-
ductive and is said to bear at times a fruit in every
leaf -axil, though part of such a huge crop is apt to drop
before maturity.

As in the case of most cultivated fruits there are
many varieties. Besides the common fig, called mis-
sion figs in California, and the well-known Smyrnas,
a California writer lists Adriatic, Eriocyne, Cordelia,
and San Pedro figs. The popular distinction into two
kinds is on the basis of color, purple or "black" figs and
yellow or "white" figs. The former are usually less
sweet and are consumed while fresh. The figs which
come dried and packed in boxes or "drums," such as
the imported Smyrna figs, are of the white variety.
They are preserved like raisins or dates by their own
high sugar content.

The fig fruit is a hollow, fleshy receptacle, with a
small opening or "eye" in the top furnishing the only
point of entry to the interior cavity. Ordinarily this
opening is almost entirely closed and barred on the
inside by a zone of small, interlocking scales. The
inner wall of the receptacle bears the very numerous,
small, simple flowers which in the edible fig are all of
the female or pistillate kind, more or less perfect. As
these grow old and elongate, they completely fill the
cavity. Each one of them normally matures a single
small dry seed which in some cultivated figs is always
sterile, in others fertile when the flowers have been
pollinated. The fruit of some varieties of the culti-
vated fig "ripens," i. e., the receptacle becomes soft,
fleshy and edible, without pollination. The fruit of
others will not ripen unless pollinated.

Pollination is a normal occurrence in the wild fig
only. This, in contrast to the edible fig {Ficus) bears
partly inedible fruit and is known as the goats-fig-tree,

[3]

4 Field Museum of Natural History

" Capri ficus" or Caprifig. It is also known as the
"male fig" because its figs or flower receptacles con-
tain male flowers in addition to the others. Female
trees of the wild fig also exist but are very scarce.
The edible fig is undoubtedly derived from such. The
male flowers of the Caprifig are situated in the upper
part of the fig cavity, immediately below the scales,
which here as in the edible fig, bar the opening to
intruders.

The insect which ordinarily inhabits the interior
of the fig cavity is the minute Fig Wasp (Blastophaga
grossorum, family Chalcidae). Through the course
of ages of association (fossil figs have been found in
remains of the Cretaceous period) the life history of
the fig and of the minute wasp have become inextric-
ably entangled. Complete interdependence has been es-
tablished between them, so that each is necessary for
the existence of the other. Without the wasp the wild
fig would soon become extinct, for there would be no
maturing of seed, and, vice versa, in the absence of
the wild figs there would be no fig wasps hatching.
The female fig wasp enters the young caprifig in which
at a certain period the orifice is relaxed, lays its eggs
in the short-styled flowers near the base of the cavity
and dies within the fig. These flowers are known as
gall flowers. The habit of response to the visitations
of the fig wasp has proceeded to the stage of anticipa-
tion, for gall flowers are not normal flowers that be-
come gall flowers through the egg-laying of the insect,
but are already present as such, though barren and
useless till the puncture of the wasp supplies them an
inhabitant in the shape of a wasp grub.

The eggs hatch into male and female wasps. The
small, yellow, wingless males mature first, bite holes
in their galls and crawl out into the cavity of the fig.
They soon cut holes in the gall flowers containing the

[4]

Figs 5

still immature females, impregnate them and shortly
die within the fig, as did the mother wasp.

Their sisters, the female wasps, are darker, of a
brown color and winged. In due course they hatch
and immediately set about leaving the cavity of the
fig within which there is no room for them to spread
their wings. To reach the orifice of the fig they must
pass the male flowers and become dusted with the
pollen that matures at the very time of their hatching
and departure.

Once in the open air their wings soon dry and each
young female wasp is off in search of an immature
fig in which to deposit eggs. A suitable one found, the
wasp proceeds to cut a notch in one of the outer scales
for better access, then makes its way inside. In the
process the wasp generally loses its wings. These are
apt to stick in the opening, so that an inhabitated fig
may be recognized by their presence. The pollen car-
ried by the insect is brushed off on the stigmas of the
long-styled flowers within. Eggs can be properly
placed only in figs of the Caprificus kind, where gall
flowers are present.

Both the wild and the cultivated fig usually bear
three crops a year. As insects emerge from one crop
of maturing Caprifigs they ordinarily find green fruit
of the next crop ready to receive them. Each crop is
thus pollinated with pollen of the preceding crop. An
interval of about two months elapses between the en-
trance of the egg-laying fig wasp into the young fig
and the emergence of her progeny from the ripe one.
The same interval of time separates the receptive stage
of the female fig flowers and the ripening of the pollen
in the male flowers, completely excluding the possibility
of self-pollination. The last of the fig wasps of the
year deposit their eggs in young fruit which stays on
the trees until spring.

[5]

6 Field Museum of Natural History

To prevent the dropping of fruit of the edible fig
before maturity, it is an ancient practice among fig
growers to hang branches of the wild fig tree, or
strings of ripe Caprifigs, in the trees of the fig orchard.
The fig wasps will then enter the young edible figs and
bring about pollination with the Caprifig pollen. The
true Smyrna fig absolutely requires pollination to ripen
its fruit. Fig trees of this variety grown in Califor-
nia continued to drop their immature fruit for over
twenty years till the wild fig with its fig wasp was
introduced and the so-called "caprification" was made
possible. In Mediterranean countries Caprifigs for the
purpose of caprification are an article of commerce
at times bringing a higher price than edible figs. It has
often been stated on apparently good botanical author-
ity that the practice is of doubtful utility. According
to the California zoologist, Eisen, who has done much
to clear up this question, the confusion is due to a fail-
ure to discriminate between the varieties which require
and those which do not require pollination in order to
mature their fruit. The latter kind are grown alto-
gether in some localities, as in southern France.

The ancients who observed the fig wasp and well
knew that it had something to do with the ripening of
the fruit, sought to account for it in accordance with
the ideas of their time., e. g., "the wasps suck up the
superfluous humors," "they enlarge the eye and per-
mit the fertilizing air to enter."

The German botanist, Solms-Laubach was the first
to investigate thoroughly the flowers of the fig and
extended his inquiries to some of the numerous species
of wild Ficus. Many of these have been studied since
and relations have been found to exist between plant
host and insect tenant similar to those observed in the
cultivated fig. The insects associated with the wild
figs are all closely related to the fig wasp of the Capri-

[«]

Figs 7

fig but distinct and different in the various species of
the genus Ficus. It would seem probable that most, if
not all, of the six hundred or more species of wild figs
throughout the world are as dependent for their con-
tinued existence on their respective fig wasp guests as

is the Caprifig.

B. E. Dahlgren.

Exhibits in the Field Museum pertaining to the Mulberry
Family and the Fig are to be found in the Department of Botany,
Halls 28 and 29, particularly, a reproduction of a fruiting branch
of the Cultivated Fig, an enlarged section of a young flower
receptacle, an enlarged section of a Caprifig with the male and
female Fig Wasps, wood and rubber of Ficus, etc.

In the Department of Geology, Hall 18, are to be seen fossil
Figs, of the Cretaceous period, from Wyoming and Kansas.

[7]

*imsrry
AUG

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