20 BRITISH APHIDES. 



appear to be a species of PemciUinm. The outer 

 surface of tlie body, to the eye, appears Hke the pile 

 of reddish velvet, which under a high magnifying 

 power resolves itself into a mass of jointed threads. 

 On cutting into the body of such an Aphis, the 

 adipose matter, usually so abundant, appears to have 

 undergone something like a saccharine degradation. 



De Bary says that the zoospores of Peronospora 

 are capable of attaching themselves to the moist legs 

 of flies and mites, and that these zoospores afterwards 

 produce on them a plentiful crop of mycelium. 



Passerini remarks that B, dianthi is one of the most 

 destructive Aphides in foreign greenhouses. They 

 there give rise to a kind of mould on the plants they 

 infest, to which the French give the name Fimiagine. 



Some have ascribed the disease peculiar to the 

 turnip plant, and variously known as Anbury, Clv.h- 

 hing or Fingers and Toes to the attacks of Aphides; 

 but, so far as I can discover, the disease is not due to 

 any Aphis attack, but probably is caused by insect 

 punctures on the tap-root when the plant is young. 

 Such wounds would probably produce excrescences 

 similar to those we find on the barks of our young 

 trees. The root of the tm^nip which, when healthy, may 

 weigh more than fourteen pounds, by clubbing may be 

 reduced to two or three ounces, whilst below the first 

 bulb numerous excrescences occur which finally 

 become half rotten. Simultaneously fibres are given 

 off the knots, each of which becomes disfigured by its 

 own dilatation. 



To satisfy myself, I searched the roots and the sur- 

 rounding earth of four such diseased plants in Sep- 

 tember. I found only five Aphides on the leaves, and 

 none on the roots. Several Elateridse and Myriopoda, 

 however, had established their quarters in the half- 

 rotten cavities, but none of these insects obviously 

 had anything to do with the " clubbing." Curtis in 

 his ' Farm Insects ' states his opinion that Aphides 

 are not the cause of this evil to the turnip. 



