4 BULLETIN 575, U. S. DEPARTMENT OE AGRICULTURE. 



these our knowledge is at present on a firm basis of experimental 

 proof. It has seemed best, however, to add to the list some plants 

 which undoubtedly produce poisonous effects, but which have never 

 been subjected to detailed experimental study. 



LOCO PLANTS. 



Without any doubt the most destructive of all the poisonous plants 

 are those going under the general name of loco. That extensive 

 losses of domestic animals have been caused by loco plants, has been 

 claimed for a long time, but it is only within the last few years that 

 exact evidence, by careful experiments, has shown definitely that 

 these plants produce the effect which has been popularly ascribed to 

 them. A great deal of interest attaches to these plants because of 

 their wide distribution and the large number of animals that have 

 been poisoned by them, including cattle, horses, and sheep, and also 

 because of the difficulty of actually proving the existence of a poison- 

 ous principle in the plants themselves. 



The loco plant has had its place in romantic literature, as it has 

 frequently been claimed that it produces the same effect upon human 

 beings as upon the lower animals, and it has been a popular subject 

 for the short-story writer. None of these stories of ''locoed" men, 

 however, has any substantial foundation. 



The word loco is from the Spanish, meaning crazy, and was given 

 to the plant because of its supposed effect upon its victims. Loco 

 plants have been heard of in practically all the open-range country 

 of the West, except in the higher mountains, and there is no doubt 

 that under the term loco disease a large number of ailments have 

 been included. Experimental proof, however, has shown that there 

 is a disease occasioned by the loco plants, with distinct symptoms 

 and with a definite outcome. 



WHITE LOCO (OXYTROPIS LAMBERTI). 



Of all the loco plants the most destructive is the "white loco," or 

 "rattle-weed," Oxytropis lamherti of the botanists. This is not be- 

 cause of its greater toxicity, but because it grows in great abundance 

 over a wide extent of territory and is poisonous not only to cattle 

 and sheep but to horses. It is found in the Plains region east of the 

 Rocky Mountains from Alaska to Mexico. Like all the loco plants, 

 it belongs to the Leguminosae or pea family, the family in which are 

 found peas, beans, clovers, alfalfas, etc. It is a perennial plant, living 

 two or three years or more, and has a long root system which enables 

 it to withstand conditions of drought. The leaflets of the compound 

 leaves are slender, more or less hairy, and of an olive-green color. 

 Thrifty plants are a foot or more in height. 



The spikes of flowers are borne on stems extending above the 

 leaves and are commonly of a prevailing white color, hence its name 



