^s"o. 479] EXTINCTION OF MAMMALIA 



789 



the influence of hunger which drives them to eat poisonous plants. 

 This justifies the consideration of plants under unusual conditions 

 of life among the possible causes of extinction. The presence 

 of molds and smuts which appear on the Gramineae, the introduc- 

 tion and spread of certain narcotic plants, the influence of ergot 

 in causing diseases of the hoof, the relation of poisonous plants 

 to increased or diminished rainfall, the introduction of certain 

 poisonous plants which while not injuring the parent afi'ect and 

 frequently kill the suckling young may be considered. Lambs 

 are frequently killed by sucking milk from animals which had fed 

 on the death camas, Zygadenus venenosus} 



Dangers Heightened by Harsh or Unusual Conditions of Life 



Poisonous plants are widely distributed. Under the unnatural 

 conditions of extreme cold, drought, enforced migration, starvation, 

 etc., it is not impossible that they may have exerted some influence 

 especially on diminishing firrds\ 'V\\v followiiio- oliscrvatioiis are 

 chiefly brought together from the papers of Dr. \ . K. ( lu'stnut of 

 the U. S. Agricultural Bureau. This aiit]ior -^lare- in a letter 

 dated July 9, 1902: "So far as my ()bscrvati..ii< ha^.■ extended 

 the chief circumstance leading to death from poixuioii^ plants 

 is an irregularity of the food supply caused l.y more or le>- umisual 

 conditions. It does not seem reasonable to suppose that wild 

 animals are frequently poisoned in their native grazing grounds. 

 Sudden disasters, however, might drive them from their feeding 

 grounds into pastures quite unfamiliar to them, where they would 

 undoubtedly be more or less at a loss to (listiuiruisli Ix'tween 

 poisonous and non-poisonous plants." 



The following observations (a, h, c) apply to .iome.tieate.l Iler- 

 bivora. 



(a) Varying Effects nj \V,t aiui Drii M.wths. A 'h,-^tm.t i "Stock- 

 Poisoning Plants of Montana" |>. I'.n observes that the 

 majority of plants known to be opeeially poisonous ihirino; the 



