OFFENSIVE OR POISONOUS PLANTS 419 



of herbivorous animals. Accordingly, great numbers of desert 

 plants are characterized by nauseating or poisonous qualities or 

 by the presence of astonishingly developed thorns (Figs. 50, 

 357), while some combine both of these means of defense. 



392. Offensive or poisonous plants. A disgusting smell is 

 one of the common safeguards which keep plants from being 

 eaten. The dog fennel (Fig. 364), the hound's tongue (Cyno- 

 glossum), the Martynia, and the tomato plant are common exam- 

 ples of rank-smelling plants which are offensive 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 

 poisonous hemlock (Conium), 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 buck- 

 thorn twigs and leaves are so bitter that browsing animals and 

 most insects let them alone. Tansy, ragweed, boneset, southern- 

 wood, and wormwood are safe for the same reason. The nau- 

 seous taste of many kinds of leaves and stems, such as those of 

 the potato, and the fiery taste of peppercorns, red peppers, mus- 

 tard, and horse-radish, make these substances uneatable for most 

 animals. Probably 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) is care- 

 fully let alone on account of the blistering nature of its contents. 



Poisonous plants are usually shunned by grown-up animals 

 unless they are famished, though the young ones will some- 

 times eat such plants and may be killed by them. Almost any 

 part of a poisonous species may contain the poison character- 

 istic 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. 



