16 BTIXETIX 969. tJ. S. DEPARTMENT OE AGEICrx/TCEE. 
the ratio of 1 to 6. There is an apparent anomaly in the dosage of 
the stems in that the much more poisonous A. galioides requires a 
slightly larger dose than Jl. mexieana. This may be explained in part 
by the fact that the stems of both plants are only shghtly toxic, but 
there is also some reason for thinking that the chemical study of 
these plants, the results of which will be published later, will offer an 
adequate explanation. 
ANIMALS AFFECTED. 
The experiments reported in this bulletin were on sheep only. 
Fle m i n g and his co-authors (1920) have shown that cattle are poisoned 
with a somewhat s imil ar dosage. From the fact that A. mexieana 
produces effects strictly comparable with those caused by A. galioides 
and that it has been shown in a previous paper (U. S. Department of 
Agriculture Bulletin 800) that A. galioides poisons horses as well as 
sheep and cattle, it is fair to conclude that A. mexieana will have the 
same effect. 
SUMMARY. 
Asclepias mexieana uhe Mexican whorled milkweed . a plant 
growing on the Pacific slope, and especially in California and Xevada. 
has long been considered a stock-poisoning plant, particularly dan- 
gerous to sheep: but there has not been definite knowledge of the 
symptoms produced by it or of its toxic dosage. 
It produces effects very s im ilar to those produced by the other 
whorled mil k weeds. A. galioides. A. pumila. and A. vertieiJIata var. 
eri. 
In toxicity A. mexieana is about equal to A. pumila and about one- 
fourth as toxic as A. galioides. The lethal dose is six times that of 
A. galioides. but about one-half that of A. pumila. 
LTTEKATUKE CITED. 
Chesnut, V. E~. IS9S. Preliminary catalogue of plants poisonous to stock. Annual 
report of the Bureau of Animal Industry. Pp. 3 ; 7-42 . 
Fleming, C. E. 1920. Project 22 — P : is mora range plants. Rpt Nev. Exp. Sta., 
p. 41. 
Fleming, C. E.. Pbtkbson, X. F., Mttt.er. M. P.. Vawtkb, E. P.. Wright. L. H. 
1920. The narrovr-leaved milkweed and the broad-leaved or showy milkweed. 
Bui. 99. Xevada Agricultural Experiment Station. 
Hut . H. M-, and Hall. C. C. 1912. A Yosemite flora. Pp. 189-190. 
Hall, H. M.. and Yates. EL S. 1915. Stcck-poisoning plants of California. Bui. 
24S Agricultural Experiment Station. Berkeley. Calif. 
Howell. T. J. 1901. A flora of Northwest America. P. 441. 
Jepsox. Wtttts T.tvv. 1911. The flora of Western Middle California. P. 323. 
Marsh. C. Dwight. Clawson, A. B.. Couch. J. P.. and Egglestok. W. "VT. 1920. 
The whorled milkweed Asdepias as a poisonous plan t. U. S. Department 
: Agriculture, Bulletin S00. 
Panimel. E. H. 3 910. A manual of poisonous plants. Part I. p. 130. 
WASHINGTON : GOTEEX XS5T PRINT! HG JKFICS 1983 
