352 FOUNDATIONS OF BOTANY 



421. Offensive or Poisonous Plants. — A disgusting smell 

 is one of the common safeguards which keep plants from 

 being eaten. The dog fennel (Fig. 227), the hound's-tongue 

 (Cynoglossum), the Martynia, and the tomato-plant are 

 common examples of rank-smelling plants which are offen- 

 sive to most grazing animals and so are let alone by them. 

 Oftentimes, as in the case of the jimson weed (Datura),, 

 the tobacco-plant, and the poison hemlock (Conivm), the 

 smell serves as a warning of the poisonous nature of the 

 plant. 



A bitter, nauseating, or biting taste protects many plants 

 from destruction by animals. Buckeye, horse-chestnut, 

 and maple twigs and leaves are so bitter that browsing 

 animals and most insects let them alone. Tansy, ragweed, 

 boneset, southernwood, and wormwood are safe for the 

 same reason. The nauseous taste of many kinds of leaves 

 and stems, such as those of the potato, and the fiery taste 

 of pepper-corns, red peppers, mustard, and horse-radish, 

 make these substances uneatable for most animals. Prob- 

 ably both the smell and the taste of onions serve to insure 

 the safety of the bulbs from the attacks of most grubs, 

 and the hard corm of the jack-in-the-pulpit (^Ariscema) 

 (Frontispiece) is carefully let alone on account of the 

 blistering nature of its contents. 



Poisonous plants are usually shunned by grown-up 

 animals, though the young ones will sometimes eat such 

 plants and may be killed by them. Almost any part of a 

 poisonous species may contain the poison characteristic of 

 the plant, but, for obvious reasons, such substances are 

 especially apt to be stored in the parts of the plant where 

 its supply of reserve food is kept. 



