78 TURNIP DISEASE. 



has made, but is thus furnished with efficient means to 

 bear it away to more hospitable places. 



(313.) To ascertain beyond all doubt that the vastator 

 of the potatoe is the same insect as the vastator of the tur- 

 nip, I have placed those obtained from the turnip on the 

 potatoe, and those from the potatoe on the turnip. From 

 this experiment I found that either plant was indifferent to 

 them ; but I noticed that the potatoe vastator seemed to 

 like the turnip better than those from the turnip liked the 

 potatoe. 



(314.) I could not help observing how much more sta- 

 tionary and tranquil this insect became when placed upon 

 the turnip ; he appeared to have got just what he' wished 

 for, and to be in a high state of self-satisfaction, not wan- 

 dering about in search of anything better suited to his 

 taste : whereas, when on the potatoe, he never seemed to be 

 quite comfortable, but would be strolling about and trot- 

 ting over the leaf, instead of sitting down at once seriously 

 to his victuals. 



(315.) The most minute microscopical examination was 

 made of the vastator from the two plants, but without 

 detecting the slightest difference of structure. 



(316.) The Swede turnip is also injured by the vasta- 

 tor ; it is, however, attacked far more sparingly by this 

 species, and to a far greater extent by the Aphis brassicse. 

 It is difficult to isolate the effect produced by the two 

 species, and therefore I did not attempt the investigation. 



(317.) A turnip, when it is growing very vigorously, 

 seems, as it were, to throw off the insect, or in fact to 

 grow quicker than the creature multiplies ; the root gets 

 the better of the attack, and the insect does not injure it to 

 such an extent. 



