2 BULLETIN 1245, U. S. DEPARTMENT OF AGRICULTURE. 
conditions poisoning took place, and to formulate methods for preventing these 
deaths. This work has involved prolonged study, and is still in progress. Some 
very definite results have been obtained, however, and it has been shown that 
the heaviest losses are due to a comparatively small number of plants. If the 
stockmen and herders can recognize these plants and will act upon the infor- 
mation contained in the bulletins which have been published on the subject, 
there is no doubt that most of these losses can be avoided. 
This bulletin has been prepared with special reference to the needs of live- 
stock producers. It was realized that many stockmen are not botanists and 
might not recognize plants through a technical description. In order To assisr 
in recognition, many of the pictures of plants have been reproduced in colors. 
The bulletin was published in 1918 as Department Bulletin 575 and proved 
to be so popular that it was reprinted the following year. Inasmuch as there 
have been considerable additions to our knowledge of poisonous plants since 
the bulletin was issued, it has seemed wise to revise it and bring it more com- 
pletely up to date. A number of pictures of poisoned animals have been added. 
This is not intended as a complete manual of the subject. For detailed in- 
formation other publications should be consulted. The United States Depart- 
ment of Agriculture has issued a considerable number of publications relating 
to specific plants. A list of such publications is given at the end of this bul- 
letin. 
Plates I. V, XI, XXII. XXIII, and XXX are from paintings by F. A. Walpole, 
in the collection of the United States National Herbarium. 
J. R. Mohler. Chief of Bureau. 
INTRODUCTION. 
Poisonous plants have been the cause of heavy losses among live- 
stock on the range. Stockmen generally have recognized the fact, 
but in the past comparatively little has been clone to avoid the 
losses. The first intimation of trouble has ordinarily been the 
finding of the carcasses, and while the men handling the stock have 
felt reasonably sure that certain plants were responsible, their 
knowledge of the plants was very meager, and the evidence against 
any particular plant was frequently insufficient. It was noticed that 
these losses were more apt to occur in certain seasons than in others, 
and it was assumed in some cases that the plant was more poisonous 
at some stages of growth than at others. Many of the stockmen 
were entirely uncertain as to what plant caused the damage, and it 
was common to speak of the source of the trouble as " poison weed," 
in a general way, without any very. definite idea as to what particu- 
lar weed Avas responsible for the loss. Moreover, the investigations 
which have been carried out on the subject of range poisoning plants 
have necessarily been somewhat narrow in scope. There is a popular 
misconception in regard to the quantity of a poisonous plant neces- 
sary to produce illness. It seems to be the general belief that any 
plant possessing poisonous properties must be violently toxic. It 
is not unusual to hear stories of poisoning of domestic animals by 
a very few leaves of a poisonous plant. As a matter of fact, most 
of the stock-poisoning plants in the United States produce illness 
only when eaten in considerable quantity. This explains why so 
many experimental tests of animals with poisonous plants have 
failed, since some of these plants can be eaten with no apparent 
harm, provided the quantity eaten at any one time is not sufficient 
to produce toxic effects. 
Many of the problems of plants poisonous to livestock seem to be 
largely peculiar to North America. Although similar plants occur 
