Poison ivy

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«. .>iiiur,i<: ilRRARY AT URBANA-CHAMPAIGN
UNIVERSITY OF IlLINOIS LIBRAKT ai

FEB 1 2 19?5

lEB 1 1 1975
loEC 0 4 198'

L161 — O-1096

POISON IVY

BY

JAMES B. McNAIR
Associate in Economic Botany

Botany
Leaflet 12

FIELD MUSEUM OF NATURAL HISTORY

CHICAGO
1926

LIST OF BOTANICAL LEAFLETS ISSUED TO DATE

No. 1. Figs $ .10

No. 2. The Coco Palm 10

No. 3. Wheat 10

No. 4. Cacao 10

No. 5. A Fossil Flower 10

No. 6. The Cannon Ball Tree 10

No. 7. Spring Wild Flowers 25

No. 8. Spring and Early Summer Wild Flowers . . .25

No. 9. Summer Wild Flowers 25

No. 10. Autumn Flowers and Fruits 25

No. 11. Common Trees 25

No. 12. Poison Ivy 25

D. C. DAVIES, Director

FIELD MUSEUM OF NATURAL HISTORY
CHICAGO, U.S.A.

LIBRARY

OF THE

L'NIVEHSITV Of ILLINOIS

LEAFLET 12.

FRONTISPIECE.

Photograph by R. E. Dahlyren.

ON RICH SOIL THE POISON IVY CLIMBS TREES BY MEANS OF ADVENTITIOUS ROOTLETS.

0.

Field Museum of Natural History

DEPARTMENT OF BOTANY
Chicago, 1926

Leaflet Number 12

Poison Ivy

Of all plant pests poison ivy, with its kindred

species, poison oak and poison sumac, are the most

dreaded. It is well known that the slightest contact

with the sap, the broken leaves and branches gives rise

to a most painful irritation and itching of the skin.

.Some persons are so susceptible that they are seriously

^affected by merely handling things that have come

r^into contact with the poison ivy, such as garden tools

r or the clothing of one who has walked through a poison

oivy patch. Few fortunate persons are naturally im-

* mune.

10 The plants that cause ivy poisoning are botani-

^cally related, in fact all belong to one genus, Rhus,

-^ which includes also the harmless and attractive sumacs

<^of our roadsides. There are three principal poisonous

'> species of this genus in the eastern United States, and

one on the Pacific Coast.*

^ The first and most common of the eastern species

^^is the poison ivy itself, known botanically as Rhus

, Toxicodendron. Its species name. Toxicodendron, is

^composed of two Greek words that mean "poison-tree."

^Poison ivy is easily distinguished by its compound

r^leaves of three leaflets. Its flowers, which appear late

in spring, are clusters of inconspicuous, greenish-white

bloom, followed by waxy white berries. The poison

*See J. B. McNair, The Taxonomy of Poison Ivy. Bot. Ser.
Field Mus. Nat. Hist. Vol. IV, No. 3, 1925.

[169]

2 Field Museum of Natural History

ivy has two principal habits of growth, being either
shrub like or climbing. In one habit, the plant comes
up as slender, stiffly erect, little branched shrubs from
winding underground stems or rootstocks. The bark
is rather smooth and light gray. The height is usually
from one to three feet, though in rich, moist places it
may reach four or five. In the other growth-habit, the
main stem clambers up trees and over rocks or walls,
sending out aerial roots that cling like those of the
true English ivy. Because of the rooting habit of this
form of poison ivy, the great pioneer botanist, Linnaeus,
who never saw the growing plant, considered it as a
separate species and gave it a separate name, Rhtis
radicans — radicans meaning "rooting" — but the pres-
ent-day tendency is to regard the vine simply as a
climbing form of a more or less variable species. In
practically all the states of the Union except California,
the poison ivy is found as a shrub where the woods are
open and rather dry, and as a vine where they are rich
and moist. Poison ivy vines with trunks nearly a foot
through grow in the "hammocks" of Florida.

Very closely resembling the poison ivy are two
species of poison oak, Rhus quercifolia of the eastern
states, found along the Atlantic Coast from New Jersey
to Texas, and Rhtis diver siloba, which grows in Cali-
fornia, Oregon, and Washington. Both of these plants
look so much like the poison ivy that some botanists
have tried to combine the three species into one.

The most vicious member, however, of this whole
undesirable clan, is the poison sumac. Fortunately,
this small tree is usually restricted to the margins of
swamps, which are seldom visited except by occasional
hunters and naturalists. Sometimes, where a road has
been built through a bog, a clump of poison sumac will
cause a great deal of trouble. Its leaves look very much
like those of the common wayside sumac, though the

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Poison Ivy 3

plants are actually not difficult to tell apart. In the
first place, the common sumac never grows in bogs,
and the poisonous variety never grows anywhere else.
In the second, the fruits, both of common sumac and
of the staghorn sumac, another ornamental variety,
are red and grow in stiff, erect clusters or panicles,
while the fruit of the poison sumac is a drooping bunch
of white berries. It is a good general rule that white
fruited species of sumac are poisonous, the red fruited
ones not.

Sometimes the woodbine or Virginia creeper,* an
ornamental vine, is confused with poison ivy and gets
undeservedly blamed. The confusion is easy to avoid.
The woodbine always has five leaflets whereas the
poison ivy has three, hence the old adage : "Leaflets
three, let it be." Moreover, the woodbine does not sup-
port itself by aerial roots like the poison ivy vine, but
climbs like a grape with tendrils terminating in disks.
Finally, its fruit, instead of being an elongated cluster
of white berries, form a drooping, flattened bunch of
purple berries.

HOW POISONING TAKES PLACE

It was formerly thought that the pollen of poison
ivy, poison oak, and poison sumac was carried by the
wind and caused the poisoning. Their pollen is, how-
ever, sticky and is never carried by the wind. Further-
more, it is not poisonous. It may in fact be rubbed on
the skin of people easily poisoned, and in no case will
poisoning take place. Experimentation has shown
that neither the bark, the plant hairs, the surface of
young branches, nor the surface of uninjured leaves
cause poisoning when touched.

*Psedera quinque folia (L.) Green, at various times called
Ampelopsis and Parthenocissus.

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Field Museum of Natural History

I

CAttadenfium Tlant, Hiliorla. 97
EDERA TRIFOI^^i^^gANADENSIS.

From J. P. Cornut, History of Canadian Plants, 1635.

THE FIRST PUBLISHED ILLUSTRATION OF POISON IVY.

Poison Ivy 5

The only part of these plants that will cause poi-
soning is the sap. If a stem be cut in half, a some-
what milky juice will be seen coming out in small drops
from the outer portions of the stem. This outer por-
tion, the bark, and soft growing layer underneath, cor-
responds to the portion of the willow branch and elder-
berry stem used for whistles. Under a microscope, the
resinous sap is seen to come from small tubelike canals
in the inner layer of this, the bast. Upon thorough
examination, it is found that a new set of these canals
forms with each spring and fall growth of wood, and
that each separate canal is surrounded by glandular
cells. These small cells pour their poisonous secretion
into the canals. The canals extend from the smallest
roots to the smallest branches and exist even within
the flowers, fruits, and leaves. In the stalk of the leaf
a row of about a dozen canals is found. The midrib
and large veins have at least one canal each. These
poison canals are found to extend out into the fine net-
work of veins in the leaf. In the fruit, which has some-
what the shape of a mistletoe berry, many poison can-
als surround the seed. It is not possible to break any
part of the plants without rupturing some of these
canals and causing the poisonous sap to come out on
the surface. The freed sap soon darkens and hardens
to a black, shiny varnish, which fully protects the
wound. An oriental relative of the poison sumac thus
gives a sap which forms the well-known Chinese
lacquer.

The young leaves of the plants are more easily
injured than the mature ones. About the time when
people, tired of being shut in all winter, are enjoying
the first warm days of spring in a search for wild
flowers, the plants are just budding out and not easily
noticed. It is especially at this time of the year that
most cases of ivy poisoning occur. When the pollen

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6 Field Museum of Natural History

was considered dangerous, ivy poisoning was thought
to be the most frequent when the ivy was in full bloom,
but blossoming does not take place until the leaves
have reached their full growth, that is, six weeks after
the plant has started to bud out. The plants are poi-
sonous all the year around, but during autumn when
the leaves become red and bright yellow, they are
most easily noticed and avoided. Cases of poisoning
are then fewer in number after the leaves have fallen,
when it is necessary to bruise the stems to get in touch
with the poison.

NATURE OF THE POISON

As the poison canals have the same structure as
the resin canals in pine trees and in other plants, so
one might expect the poison to be of a resinous nature.
The latest work* on the nature of the poison gives the
information that the poison, if not a resin, is at least
intimately mixed with a resin. It is a clear amber-red,
sticky, non-volatile liquid which floats on water. This
sticky substance will adhere to the skin like pitch and
is as difficult to remove,

SUSCEPTIBILITY TO THE POISON

It has been found that only about one person in
eighteen is badly poisoned by ordinary contact with
the sap. The resistance to poisoning appears to run
in families. In some families all members are easily
poisoned. In other families no cases of poisoning take
place. In still others, one parent may be easily poi-
soned, while the children may not be susceptible, or
some children may be easily poisoned. Generally if

* Those interested in the detailed discussion of poison
ivy, its poison and treatment are referred to the book, Rhus
Dermatitis, by James B. McNair, University of Chicago Press,
Chicago, Illinois.

[174]

Poison Ivy

From Host and Gilg.

FLOWERS AND FRUIT OF POISON IVY.

8 Field Museum of Natural History

both parents are not easily poisoned, the children are
also resistant. However, if the pure poison is placed
on the skin of a person considered immune, poisoning
will take place. Others who have studied the subject
find that a person may be easily poisoned one year and
not easily poisoned sometime later. The reverse is
also known to be true. Many people, wishing to gain
resistance to the poison have chewed the leaves of the
plant, or swallowed tea made from the leaves. This
has been followed by severe cases of internal poisoning.
It is doubtful if immunity to the poison can be acquired
in this manner, as the poison is not a protein and no
other substances are known to produce immunity. A
susceptible person may certainly be severely poisoned
repeatedly during the same year. Immunity seems
to be mostly a matter of thickness and condition of the
skin. Animals are generally not susceptible. Goats
will thrive on it. Cattle and horses are known to eat
it without ill effects.

DESCRIPTION OF THE DISEASE

The poison may penetrate the skin by means of
the sweat glands, the oil glands, the hair follicles, or
even the surface of the skin itself. In from twelve
hours to a week after the poison has been placed on
the skin, a reddening and itching is noticed. The poi-
soning may never be more severe than this or it may
cause blistering. If blisters form they may break and
allow the serum to run freely over the surface. After
about a week this condition disappears and the injured
skin falls off in flakes. The poisoning is most often
experienced between the fingers, on the back of the
hands, on the forearms, or on face. It is very seldom
that poisoning takes place in those portions of the body
thickly covered by hair, although it may affect any

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Poison Ivy

10 Field Museum of Natural History

part of the body surface. The inside of the hands and
soles of the feet are seldom poisoned because of their
thick covering of skin. The ears may swell up to a
large size and the eyelids may become so swollen as to
interfere with vision. The changes in the skin caused
by this poison are not easily distinguished from con-
ditions caused by other skin poisons and skin diseases.
If a person has been in a locality where poison ivy
grows, it is likely that poison ivy is the cause. The
distribution of the blisters on the skin is generally in
strips or patches caused by contact with the plant.

REMEDIES FOR IVY POISONING

Numerous methods of treatment for ivy poisoning
have been used in the past. There is no real cure or
preventative that will take the place of caution. The
various salts of lead and zinc have been used as poison
ivy remedies. They neutralize the poison to a certain
extent, but not completely. The best and most effective
preventative proves to be salts of iron, particularly iron
chloride, which completely neutralizes the poison,
though is effective as a remedy only if used in the very
early stages. The use of iron chloride to the extent of
five percent in a half and half mixture of alcohol and
water is recommended. If the hands and face are
bathed freely in this solution either before or imme-
diately after one goes into a region known to contain
poison ivy or its kindred plants, no ill effects need be
expected. The remedy is cheap, is easily obtainable at
any drug store, is non-poisonous and safe.

In ivy poisoning cases that actually develop and
become acute the treatment is based on a recognition
of the nature of the injury. The effects of ivy poison-
ing on the skin are much like those of a burn, and the
treatment suggested resembles that successfully used
during the war in burn cases. The affected parts are
first bathed with iron chloride solution, to neutralize

[178]

Poison Ivy

11

SECTION THROUGH LEAF-RIB. THE POISONOUS RESIN IS CONTAINED
IN THE CENTRAL DUCT.

SECTION THROUGH STEM SHOWING THE RESIN DUCTS (BLACK).

12 Field Museum op Natural History

the poison. Then the skin is dried, and melted paraffin
painted over it. A thin sheet of cotton is laid over the
wound, and this also is covered with paraffin. The af-
fected area is thus protected from the air and from
rubbing, and new skin is given a chance to form.

ERADICATION OF THE PLANT

For the eradication of the plants, the U. S. Dept.
of Agriculture recommends spraying with kerosene or
sodium arsenite solution or treating the cut stems with
sulphuric acid.

In the Field Museum poison ivy plants reproduced in fruit
and flower and models of the enlarged flowers produced in the
Stanley Field Plant Reproduction Laboratories of the Museum, are
to be found together with an exhibit of other plants of the Sumac
family in the Hall of Plant Life, Hall 29 on the second floor east.

The poisonous juice of the related lacquer tree, lacquered
ware and economic products from the poison ivy relatives are with
the plant economic exhibits in the adjoining Hall 28.

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