UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 942 



Contribution from the Bureau of Animal Industry 

 JOHN R. MOHLER, Chief 



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Washington, D. C. 



PROFESSIONAL PAPER 



May 4, 1921 



POISONOUS PROPERTIES OF THE WHORLED 



MILKWEEDS ASCLEPIAS PUMILA AND 



A. VERTICILLATA VAR. GEYERI. 



By C. Dwight Marsh, Physiologist in Charge of Investigations of Stock Poison- 

 ing ty Plants, and A. B. Olawson, Physiologist, Pathological Division. 



PURPOSE OF PAPER. 



As stated in Department Bulletin 800, " The Whorled Milkweed 

 (Asclepias galioides) as a Poisonous Plant" (pp. 5 and 6), there are 

 certain other species of whorled milkweed closely related to A. 

 galioides. These species have a fairly wide distribution in the United 

 States and it is a matter of considerable interest to know whether they 

 have poisonous properties similar to those found in A. galioides. 

 While hitherto these other species have not been examined experi- 

 mentally, there has been good reason to suspect some of them of 

 being connected with losses of livestock. 



Experimental work on two species, A. pumila and A. verticillata 

 var. geyeri, has now demonstrated their toxic character, and also has 

 brought out quite definitely the character of their action as compared 

 with A. galioides. In this bulletin are summarized the results of the 

 experimental work on these plants. The work accomplished indi- 

 cates that A. pumila is about one- third as toxic as the very poisonous 

 A. galioides, and A. verticillata var. geyeri is less poisonous, being 

 about one-tenth as toxic as A. galioides. 



DESCRIPTION OF ASCLEPIAS PUMILA. 1 



Asclepias pumila (PI. I) may be called low whorled milkweed, or 

 Great Plains whorled milkweed. The stems, which are often 



1 In conformity with the cooperative arrangement between the Bureau of Plant Industry 

 and the Bureau of Animal Industry in regard to investigations of poisonous plants, the 

 material on which this paper is based was collected by W. W. Bggleston, Bureau of Plant 

 Industry,, and the description of Asclepias pumila, and that of A. verticillata var. geyeri, 

 on page 10, were prepared by him. Mr. Eggleston has made a detailed study of the 

 systematic position and distribution of these plants, which it is expected will be pub- 

 lished later. 



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