Cultivation of Arable Land. Potatoes. Difeafes of. Curl. 1 1 f 



tinue to improve till the ftems have decayed fo as to be of no utility, but ceafe the 

 inftant they are deprived of them.* 



Curl* Befides the injury that may arife to crops of this fort from the above 

 practice, they are frequently liable to be much hurt by the curl-, a difeafe in which 

 the leaves of the plants are, as it were, fhrivelled or curled up, and the healthy 

 appearance and vigour of the crop greatly impaired. The reafon of this perni 

 cious vegetable affection appears not yet fully inveftigated, as it has been a- 

 cribed to many different caufes by writers on hufbandry. Mod of the early- 

 authors confidered it in general as originating from diftempered feed, which 

 caufed it to appear in the crops wherever it was made ufe of. But in an in- 

 terefting paper in the fccond volume of Communications to the Board of Agri 

 culture, it is fuggefted as proceeding from imperfect culture, or fuch circum- 

 (lances as have a tendency to leflen and impair the vigor of the growth of the 

 plants; as the improper nature of the foil, or the want of fufficient preparation 

 of the land on which the crops are grown. It has likewife been fuppofed to 

 owe its origin to the continued propagation of potatoes by fubterraneoos buds, 

 or root-wires, iaftead of feed, as by fuch means they acquire hereditary dif 

 eafe j as happens in gardening, in the cafe of canker, to fuch apple-trees as have 

 been a great length of time propagated by grafting the fcions. In oppofition to 

 this, it has, however, been maintained by fome cultivators, that they have found 

 the curl to prevail in the potatoe plants in fuch crops as had been raifed from 

 feed of the fecond year. By others it has alfo been afTerted that infects at 

 tacking the leaves may be the caufe of the curl ; and ftill others, that the pota 

 toe roots, the leaves of which are attacked with the curl, remain hard and lefs 

 diflbluble in the foil.-j- 



And it has lately been contended, that this difeafe in potatoe crops proceeds 

 from infects beneath the ground deftroying the nutritive part of the fets after 

 they are depofited in the foil-; as it was found that from a potatoe planted in a 

 field as feed, there proceeded four ftems, two of which were weak and delicate, 

 having their leaves attacked with this difeafe, while the other two were in a 

 highly vigorous fbate, and their leaves frefh and free from the curl. On the 

 root being taken up, it was difcovered, that all the part from which the curl- 

 leaved ftems proceeded was excavated, the fubftance being wholly confumed 

 by infects. And on more frequently examining fuch roots as had their leaves 

 affected, it has constantly been found that they have been deflroyed by infects 

 cither of the fnail, centipede, or beetle kind. Sometimes it is, indeed., fup 

 pofed, that the difeafe may be caufed by the leaves only becoming the prey oi 



* Campbell, in Bath Papers, v.ol, IX, + Pyteology, p. 175. 



