THE STRUGGLE FOE EXISTENCE. 



207 



respiration take place. Some of the more or less spherical 

 cacti of the dry and treeless plains of the West contain so 

 much stored-iip water that men and animals cut or tear them 

 open for the sake of drinking from their pulpy interior. 



Arctic plants are sheltered from the savage storms of 

 winter by their habit of clinging to the ground : the Arctic 

 willow, for example, Tig. 185, is only a few inches high. 



249. Defenses against 

 Attacks of Animals. — Some 

 seeds are bitter or otherwise 

 unpalatable, others poisonous, 

 and still others so hard as to 

 be utterly uneatable. The 

 entire plant is often protected 

 from herbivorous quadrupeds, 

 snails, or destructive insects 

 by the same safeguards which 

 are found in seeds. Walking 

 through a pasture, one may 

 find clumps of buttercups, 

 tansy, ragweed, boneset, dog- 

 fennel, smartweed, or ox-eye 

 daisy ^ which cattle and horses 

 in general will not touch 

 because they are so bitter, pun- 

 gent, or ill-smelling. Three 

 of the weeds that flaunt them- 

 selves luost generally in barn- 

 yards in the Middle States are dog fennel, Jimpson (James- 

 town) weed, and smartweed. The two former are nauseating 

 to the smell and taste ; the Jamestown weed is violently 

 poisonous, and the smartweed has a savagely biting flavor. 



Fig. 186. —Thorny Branohes of Broom. 



1 These species would not aU occur in any one pasture, but they are types, apij 

 gome of them range widely over the country. 



