76 TURNIP DISEASE. 



plant, and the disease does not appear to manifest itself 

 very decidedly till the vegetable is depositing woody fibre. 



(306.) We leave potatoes in the ground till the plant 

 has run its course, has fruited and exhausted itself; whilst 

 the turnip is employed in the first period of its growth, 

 when it is but half developed, and before it has fruited and 

 become exhausted. Notwithstanding this difference, how- 

 ever, the vastator destroys great masses of turnips, and 

 causes them so to rot as to be totally unfit for use. 



(307.) The turnip plant exhibits fungi, which come 

 upon the leaf after the attack of the vastator, and thus we 

 have another analogy between the potatoe and turnip dis- 

 ease. Berkeley has figured a fungus which he found on 

 the Swedish turnip. 



(308.) The vastator generally feeds upon the under 

 surface of the turnip leaf, for, being a restless insect, im- 

 patient of the slightest intrusion, it generally crawls to the 

 under side. In a sitting-room they feed indifferently upon 

 either side of the leaf. 



(309.) There is another Aphis which feeds commonly 

 upon the turnip, and which is also highly destructive to it, 

 but which we must be careful to distinguish from the vas- 

 tator. This insect, which is apparently the Aphis brassi- 

 cse, may be known from the vastator by its whiter color, 

 by its shorter antennae, by its short abdominal tubercles, 

 and by its more gregarious habit, the insects feeding in 

 companies very closely together, like a flock of sheep, and 

 seldom jnoving from their situation. The winged speci- 

 mens may often be found dead in the midst of their off- 

 spring. 



(310.) The Aphis brassicse presents the peculiar ros- 

 trum and suctorial apparatus which I have before described 



