222 EXPERIMENTS WITH PLANTS 



(Sedges, Grasses, Holly, Century Plant), or the stip- 

 ules of the leaf modified into thorns (Locust) , or the 

 whole transformed leaf (Barberry), or a transformed 

 branch (Hawthorn, Honey Locust). 



(b) Bitter or poisonous substances. It would be 

 very interesting to know how animals, both wild and 

 domestic, learn to avoid poisonous plants. Many 

 plants have a disagreeable or offensive odor which 

 warns them away, as the Jimson Weed or Thorn Apple, 

 and many others. Many have a disagreeable taste, 

 e. g., Poppies. 



But there are many others which to us have neither 

 disagreeable taste nor odor, and yet are avoided by 

 grazing animals of all kinds. In this respect their in- 

 stincts are superior to ours. There are some poisonous 

 plants, notably the "loco weeds," which are eaten by 

 domestic animals and which produce dizziness, vertigo 

 and insanity. It is stated on good authority that the 

 loco habit may be taught by a single animal to a 

 whole herd, and that an animal which has been appar- 

 ently cured of the habit by treatment is never entirely 

 trustworthy thereafter. 1 



In general, however, poisonous plants are avoided, 

 and the same is true of many plants which are bitter or 

 disagreeable without being poisonous (e. g., Worm- 



1 The annual loss from poisonous plants on the western stock ranges is 

 about $400,000. See the article by Chestnut, in the Year Book of the U.- S. 

 Department of Agriculture for 1900. 



