15 



THE NARROW-LEAVED MILKWEED (Asclepias Mexicana) 

 The Part of the Plant Which Is Poisonous. 



In our experiments we have fed the whole top of the plant, stems, 

 leaves, and sometimes flowers and seed pods. A few feedings were made 

 of leaves only,, and these few tests seem to indicate that fee leaves are 

 the most poisonous part of the plant. The pods appear to be less 

 poisonous than either the leaves or the stem. Feeding of seeds alone 

 produced no symptoms. This indicates that the plant is not more 

 dangerous, but perhaps less so, when it is full of seed pods than at 

 other times. For all practical purposes the entire plant may be 

 considered poisonous. 



The Time of the Year When It Is Poisonous. 



So far as known the narrow-leaved milkweed is poisonous at all 

 stages of growth. Our tests showed it to be poisonous when fed (1) in 

 a green condition, (2) after being cut and dried as hay, and (3) as it 

 dries naturally in the field in the fall. Thus in all stages it is poison- 

 ous; and hay containing any large amount of this plant may be 

 regarded as extremely dangerous. 



Amount Necessary to Make Sick or to Kill. 



We fed the narrow-leaved milkweed to cattle and sheep, (1) in a 

 fresh green state, (2) after being cut and dried, and (3) as it cured 

 naturally on the stems in the fall, (4) the pods alone, and (5) the seeds 

 alone. 



TABLE I 

 The Narrow-Leaved Milkweed The Fresh Green Plant Fed to Sheep 



The animals were not watched during the night, usually the first observation being made at 

 8 o'clock in the morning. This is the reason why, in this and the following tables, under the 

 caption Time of Death or Recovery, "8 : 00 a,, m." appears so often. It records the condition of 

 the animal at the first observation made in the morning. 



The tests summarized in this table indicate that ( 1 ) if common range 

 ewes eat one-half pound or less no -serious trouble will follow; (2) 

 amounts in excess of one-half pound and up to 1J pounds will usually 

 make the animal sick, but it will recover; (3) amounts of 1^ pounds 

 or more are quite likely to cause death. 



