MEXICAN WHORLED MILKWEED AS A POISONOUS PLANT. 



15 



It is evident that the toxic principle of the plant is found very 

 largely in the leaves. 



A comparison of the preceding figures with the toxic and lethal 

 dosages for sheep given in Nevada Bulletin 99 can be made by- 

 reducing the dosage in Table I, page 15, of the Nevada bulletin to 

 pounds per hundredweight of animal. It will be seen that the 

 smallest toxic dose, 0.537 pound per hundredweight in the case of 

 Sheep 25, is somewhat smaller than the figures obtained in our 

 experiments. It may be noted, too, that Sheep 75 received 0.555 

 pound without effect and that the smallest lethal dose was 2.3 

 pounds in the case of Sheep 6. 



If the data of Table II of the Nevada bulletin giving the feedings 

 of air-dried plant are similarly reduced to a dosage for 100 pounds 

 of animal and an allowance of a loss of 75 per cent by evaporation is 

 made, as in our work, the smallest lethal dose would be 2.059 pounds 

 in Sheep 72 and the smallest toxic dose 1 pound in Sheep 59. 



The dosage in Table III (Nevada) of material which had dried in the 

 field is somewhat larger, the lethal dose, 7.5 pounds in Sheep 43, 

 being especially large. This is probably accounted for by the fact 

 that there had been some loss of leaves in the field, for it is shoA\Ti on 

 page 14 of this paper that the leaves are especiall}' toxic. 



Table 7 shows the comparative toxicity of the different whorled 

 milkweeds : 



COMPARATIVE TOXICITY OF SPECIES OF WHORLED MILKWEED. 



Table 7. — Comparative toxicity of different species of whorled milkiveed. 



Species. 



Minimum 



toxic dose 



of whole 



plant. 



' Pounds. 



A. mexicana 0. SS2 



A. galioides 0. 22 



A. piimila 0. 7S7 



A. verticillata var. geyeri 2. 205 



Minimum 



lethal dose 



of whole 



plant. 



Pounds. 

 1.323 

 0.22 

 2.165 



Minimum 

 toxic dose 

 of leaves. 



Pounds. 

 0.353 

 0. 138 



Minimum 

 lethal dose 

 of leaves. 



Pounds. 

 0.SS2 

 0. 13S 



Minimum 

 toxic dose 

 of stems. 



Pounds. 

 1.323 

 1. 543 



1.2S6 



Wliile too much reliance must not be placed on this table as show- 

 ing exact relationships, nevertheless it indicates, in a general way, 

 the relations between the species. So far as the whole plant is con- 

 cerned, A. mexicana and ^1. pumila are about equally toxic. 

 A. galioides is 4 times as toxic as these two species and 10 times as 

 toxic as A. verticillata var. geyeri. As regards the lethal dose of the 

 whole plant, ^4. galioides is 6 times as toxic as A. mexicana and 9.84 

 times as toxic as .1. pumila. 



With relation to the leaves, A. galioides and A. verticillata var. 

 geyeri compare much as in the whole plant; that is, in a ratio of about 

 1 to 10. The ratio of A. galioides to A. mexicana, however, is 1 to 

 2.56 instead of 1 to 4, as in tlio whole plant, while the lethal dose is in 



