ADAPTATION 



231 



production of red clover, and since cats destroy mice they are 

 beneficial to its production. 



INIodcrn economic biology is full of such illustrations. We spray 

 plants to get rid of aphids, but it is often necessary to destroy a 



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Fig. 138. — Flying squirrel, Sdiiropterus volucella. (From Lull.) 



neighboring ants' nest before a cure can be accomplished, for the 

 ants may bring other aphids to replace those killed by spraying. 

 We also poison, trap and swat the fly, but if horse manure is piled 

 in the neighborhood, we can destroy more flies with less effort by 

 having it removed. We raise fruit, and many orchardists have 

 found it to their advantage to rent bees to be placed in their 

 orchards during blossom time, in order that cross fertilization 



