UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1212 
Washington, D.C. April 29, 1924 
THE WOOLLY-POD MILKWEED (ASCLEPIAS ERIOCARPA) AS A 
POISONOUS PLANT. 
By C. DwicHt MArsH, Physiologist in Charge of Investigations of Stock Poison- 
ing by Plants, and A. B. CrAwson, Physiologist, Pathological Division, Bureau 
of Animal Industry. 
CONTENTS. 
Page Page 
Weseripiion of the. plant _2=-—_-——-_ 2 | Results of experimental work and 
Experimental work___ z 4 conclusions—Continued. 
Typical case of sheep God 1 2 4 Autopsy, findings! 22 itll 
Results of experimental work and Microscopic changes in tissues_ idl 
ConelIsionus, 23 se 6 Toxic and lethal dosage_______ 13 
NOES et 6 Comparative toxicity of leaves 
Delay in development of symp- ANG SCAMS Sle ee Sa = Ss 13 
Pema rte po 2 CS 9 ATMA Swealrected © ==. 7 es— aa tS 
Duration! of: sickness———=_= 2 —= 10 SS) ULNA aes eee eed ee UE tS 13 
Many statements have been made by California stockmen in regard 
to the loss of range animals, especially sheep, by milkweeds. These 
statements generally were not in regard to any particular species, 
but simply about plants popularly known as milkweeds. That these 
losses actually occurred there was no doubt, and there seemed as 
little doubt that they might be connected with particular species. 
Department Bulletin No. 969 of the United States Department of 
Agriculture deals specifically with the Mexican whorled milkweed, 
which has a widespread distribution in California, and shows con- 
clusively its extremely poisonous character. Among other milkweeds 
the woolly-pod milkweed, Asclepias eriocarpa, has “been supposed to 
be connected more or less definitely with losses of sheep. Through 
the kindness of Prof. H. M. Hall, of the Carnegie Institution, Wash- 
ington, D. C., a considerable quantity of this plant was obtained and 
experimental work carried out in some detail, which has cleared up 
the facts in regard to the poisonous properties of the plant. The 
work is the subject of this bulletin. 
Very little has been published in regard to the poisonous properties 
of Asclepias eriocarpa. Apparently the first statement in print was 
that made in 1890 by Prof. E. W. Hilgard in The Weeds of Cali- 
fornia, in which he states: 
A. fremonti and eriocarpa, and locally Gomphocarpus tomentosus, maintain 
themselves in pastures, to the occasional detriment of sheep and cattle that 
are tempted to vary their dry summer diet with something green, and are 
poisoned by eating the leaves of these milkweeds. 
63982°—24 
