74 PRIZE ESSAY : 



ground. It is a very obscure subject, requiring an extended 

 series of very careful observations to lead us to the exact truth. 

 And in such enquiries as this we are very liable to be misled, and 

 to mistake mere coincidences for established laws. For instance, 

 if an insect has been observed in two or three instances to be very 

 numerous, say, after an unusually wet season, we should confi- 

 dently conclude such a season to be the cause of its multiplica- 

 tion. But it may perchance again show itself in equal abun- 

 dance after a dry season. Authors have so often been humiliated 

 by having their speculations falsified in ways analogous to this, 

 that I have felt disinclined to venture ujjon such precarious 

 ground, except with the utmost caution. It is a most importaiat 

 topic, however, and all the facts which fall under our observation, 

 having a bearing upon it, should be recorded, and in time such 

 records will lead to correct theories in the premises." 



131. There can be no doubt that the excessive and continuous 

 cultivation of its favourite food, wheat, without rotation, has 

 fostered, encouraged and cherished the Hessian fly, and indeed, 

 all other wheat depredators, vmtil they have become firmly estab- 

 lished in the country, and always to be looked for and guarded 

 against. Little or no rotation has been allowed to interfere with 

 their progress. They have been provided with all situations of 

 exposure or shelter in one locality or another, to ensure the pro- 

 pagation of their species ; and all that the sensible farmer can 

 do to protect himself from the swarms which will continvially be 

 thrown ofF from the nurseries maintained through selfishness 

 or ignorance in this country, is to adopt the artifices which ^^^ill 

 enable him to escape the attacks of the depredators. 



132. It has been suggested that the name 'Hessian Fly' should 

 be discontinued and the term ' wheat stem-fly, substituted for it. 

 The change, however, is decidedly objectionable, on the ground 

 that there exists in Europe an insect which has long borne the 

 name of the ' wheat stem-fly,' (chlorops pumilionis.) 



