THE STRUGGLE FOR 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-up 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, Fig. 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- Fic. 186.—Thorny Branches of Broom. 
selves most 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. 
1 These species would not all occur in any one pasture, but they are types, and 
some of them range widely over the country. 
