S66 PRINCIPLES OF GARDENING. [cH. VIII, 



affected; and the same observers record, that it 

 appears in soils that have not produced turnips for 

 a long series of years. The diseased specimens 

 examined by Mr. Marshall, were from an old orchard 

 that had not borne turnips ^rithin the memory of 

 man. 



Mr. Spence concluded, that the disease is occa- 

 sioned by the poisonous wound inflicted by some un- 

 ascertained insect upon the turnip in an eai'ly stage 

 of vegetation, or by its insinuating its egg into it, 

 infusing at the same time a liquid, causing a morbid 

 action in the sap vessels, and the consequent forming 

 of excrescences. This correct opinion was afterwards 

 confiiined by the actual discoveiy of the insect, 

 and that there actually is a maggot generated 

 from the egg, of which fact, at the time, he was 

 entirely ignorant. 



The maggot fomid in the turnip ambury, is the 

 larva of a wee\il called Curculio pleiirostigma by 

 Marsham, and Rhynchcenus sulcicollis by Gyllenhal. 

 " I have bred this species of weevil " says Mr. Kirby, 

 "from the knob-like galls on turnips, called the 

 ambury, and I have little doubt that the same insects, 

 or a species allied to them, cause the clubbing of 

 the roots of cabbages ^. 



Marsham describes the parent as a cleopterous 

 insect, of a dusky black colour, with the breast 

 ' Kirby and Spence's Introduction to Entomology, i. 450. 



