2 BULiLETIN 1245, U. S. DEPARTMENT OF AGRICULTURE 



ihe heaviest losses are due to a comparatively small number of plants. If the 

 stockmen and herders can recognize these plants and will act on 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. Ir was realized that many stockmen are not botanists and 

 might not recognize plants through a technical description. In order to assist 

 in recognition, many of the pictures of plants have been reproduced in colors. 2 



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. 



Plates 3, 8. 12. 31, 32, and 38 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 comparatively little has been done to avoid the losses. The iirst 

 intimation of trouble has ordinarly 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 fre- 

 quently insufficient. It was noticed that these losses were more apt 

 to occur in certain seasons than in others, and in some cases it was 

 assumed 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, in a 

 general way, of the source of the trouble as " poison weed." without 

 any very definite idea as to what particular weed was responsible for 

 the loss. Moreover, the investigations which have been carried out 

 on the subject of range poisoning plants have necessarily been some- 

 what narrow in scope. There is a popular misconception in regard 

 to the quantity of a poisonous plant necessary 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 quan- 

 tity. 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 

 in the eastern continents, very little information can be drawn from 

 European sources to aid the American stockman. 



For several years the United States Department of Agriculture has 

 been carrying on a series of experiments with poisonous plants, and 



2 F. V. Coville. of the Bureau of Plant Industry, has read the manuscript with special 

 reference to the identification of the plants and to the common names which should bo 

 applied to them. 



