THE STRUGGLE FOR EXISTENCE 379 



broken trees, flattened grain, upturned nests of birds, drowned 

 nestlings, and insects killed by wind or water. The small and 

 inconspicuous forms of life that are killed are more numerous 

 than the larger ones. At other times sudden changes in tem- 

 perature prove extremely destructive. When migratory birds 

 are caught in snowstorms many die. The American golden 

 plover flies southward in the autumn migration over the 

 Atlantic Ocean from Nova Scotia to the Lesser Antilles or 

 even to South America. Often these birds are caught in 

 heavy storms, many doubtless perishing at sea and many 

 being driven ashore in an injured condition. Rainstorms 

 accompanied by hail cause the death of young birds, insects, 

 and some larger animals, and of large numbers of plants. 

 Excessive heat, drought, and other climatic causes are im- 

 portant factors in the elimination of living things. 



391. Destruction by disease. A visit to a corn field or 

 wheat field will usually enable one to discover a parasitic plant 

 known as smut growing upon the corn or wheat. This smut 

 secures its nourishment from the host plant. After a time 

 it produces its reproductive spores, by means of which new 

 smut parasites may get started on new host plants. But the 

 host plant suffers and may be killed by the smut. Its supply 

 of nourishment may be taken by the smut, or the smut may 

 produce poisonous substances that severely affect the host. 

 The smut is merely growing in its own way, but in so doing 

 it may cause the death of other plants. 



Bacteria, fungi, and some animals cause the disease and 

 death of other living things. So universal is disease that we 

 scarcely know what is meant by " natural death." In nature, 

 when animals begin to get old and their bodies operate less 

 effectively than when they were younger, they are more 

 readily captured by food-seeking animals or are more suscep- 

 tible to disease. In nature so-called natural death of animals 

 is rarely if ever seen, since they are usually killed by their 

 enemies or by disease. 



