Nature Bulletin No. 276 October 1, 1983
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
In the autumn of 1818, Nancy Hanks Lincoln died of milk sickness
and left her son, Abe, motherless before he was ten years old. Since
colonial times, in most of the eastern half of the United States, that
dreaded disease has been a hazard in summer and fall, wherever cattle
graze in woodlands or along wooded stream banks. In the 1920s it was
finally traced to white snakeroot -- an erect branched plant, usually
about 3 feet tall, with a slender round stem, sharply-toothed nettle-like
leaves and, in late summer, several small heads of tiny white flowers.
Cows eating small amounts over a long period develop a disease called
"trembles", and their milk may bring death to nursing calves or milk
sickness to humans. When larger amounts are eaten the cow, herself,
Plants, ordinarily, are useful or harmless but a surprising number
produce poisons. The U. S. Forest Service lists more than 500 species
in this country but most kinds are poisonous only when eaten by man
or domestic animals. In many cases, only one or more parts of the
plant are poisonous -- perhaps only at certain seasons of the year or
under certain conditions. The greatest danger to livestock occurs In
early spring or in late summer and fall when pastures are scanty and
the animals are tempted to eat weeds or leaves they otherwise avoid
when tastier forage is plentiful. In the west, considerable losses among
livestock are caused by many kinds of Locoweed which concentrate, in
their leaves and stems, dangerous amounts of selenium and other
poisonous minerals from the soil; also by many species of Wild
Larkspur, and the Death Camass.
A few plants, like nettles, poison oak, and the poison sumac which
grows in bogs, do not affect animals but cause severe rashes and
blisters when touched by some people -- not all. Occasionally, people
are found who are allergic to fruits such as strawberries or paw paws.
or to foods made from buckwheat flour. Some develop a skin affliction
from contact with the milky sap of the osage-orange tree, or certain
plants of the spurge family.
Poisonous plants are scattered through many plant families in which
most of their relatives may be harmless. Socrates was condemned to
die by drinking a brew of Poison Hemlock, a member of the parsley
family, now common in this country. The roots of the Water Hemlock,
another common member, often mistaken for wild parsnip, are
violently poisonous to humans and livestock. The fruits and generally
the foliage of several members of the Nightshade family. Including
Bittersweet and Jimson Weed, are poisonous.
The leaves of Johnson grass, sorghum cane, flax, and wild cherry trees
contain a harmless substance which, when the leaves wilt, produces
the fatal prussic acid. Several cultivated ornamental plants -- such as
the lily-of-the-valley, larkspur, narcissus and English ivy -- are
poisonous when eaten. So are some of our common wild flowers like
the Dutchman's Breeches, Bouncing Bet, Skunk Cabbage and Jack-in-
the-pulplt. The latter two have a pungent juice which painfully burns
the mouth, throat and stomach but the Indians were able to destroy the
poison and used these plants for food -- just as tropical Indians use the
deadly cassava root from which we get tapioca.
There are several kinds of plant poisons, with different effects upon
animals, including people. No one knows why they are produced by
certain plants. Many, however, are also our sources of useful drugs
such as quinine, digitalis, bella-donna, strychnine and morphine.
Maybe a dangerous weed is only a plant misused.
To return to the Nature Bulletins Click Here!
Update: June 2012