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FEB 1 2 19?5 

lEB 1 1 1975 
loEC 4 198' 

L161 — O-1096 



Associate in Economic Botany 

Leaflet 12 




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 







Photograph by R. E. Dahlyren. 



Field Museum of Natural History 

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. 


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 


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. 


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. 


Field Museum of Natural History 


CAttadenfium Tlant, Hiliorla. 97 

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


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 

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 


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. 


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, 


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. 


Poison Ivy 

From Host and Gilg. 


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. 


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 

[ 176 J 

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. 


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 


Poison Ivy 




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. 


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.