Cultivation of Arable Land.-jrheatSmut-Ufeof.-Frec Circulation of Airing 



But though thefe methods may be employed in order to prevent the propa 

 gation of the difeafe, it is probable that it can only be effectually guarded 

 againft by fovving the feed in fuch a manner as to admit of a perfectly free cir 

 culation of air among the plants, and of thofe modes of after-culture that are 

 adapted to promote their healthy and vigorous growth. 



peatcd the following feafon, and with nearly the fame refult. Satisfied with knowing that complete, 

 wafliing would be found a remedy for the difeafc, lie made no farther enquiry upon the fubjed till 

 lali autumn, when he was employed in making obfervations on the blight, in the couri e of which, 

 he met with a good deal of fraut in many fields ; and being at the time pofl cfied of fume excellent 

 glafi es, he carefully examined fome of the fmutted plants. This at firft was clone more as a matter of 

 amufement, than from an expectation of difcovering any thing that might contribute to throw light 

 upon the fubjecl. Upon a near infpeclion with the g!afs, he found that the dirty green colour of the 

 blades of the fmutted ears was owing to a number of fpots infinitely fmall, and bearing a near refem- 

 blance to thofe upon blighted ears: his obfervations were continued throughout the whole period of 

 the ripening, in the courfe of which he made no additional difcovery, except obferving, that the 

 leaves and ftalks of the fmutted ears decayed fooner than fuch as were healthy. 



About the end of autumn, however, having one day brought home fome fmutted ears of rather ar 

 unufual appearance, he examined them rery narrowly, and obferved that the balls were perforated in 

 many places with final I round holes, a thing he had not before obferved in any that he had met with : 

 this he afcribcd to vermin ; and upon fricking one of the grains upon a pin, and placing it under the 

 glafsina very bright fun, he could diftindly obferve feveral fmall tranfparent fpecks upon the beard, 

 or downy part of it. He examined feveral more, and met with exactly the fame appearance ; but be 

 ing called haftily away, upon bufinefs, he was under the neceflity of leaving them upon the table, with 

 out being able to afcertain whether the objects he had feen were eggs or infects. In the evening when 

 he came home, he refumed the inveftigation by candle-light ; in the courfe of which, as he was under 

 the necefiity of holding them very near the candle, the heat foon relieved him from embarraffment, 

 by putting them in motion, and he then difcovered that the fpecks above mentioned were real infecls, 

 refembling wood-lice in fhape. Next day he repeated the fame trials by fun light with new fmut- 

 balls, and difcovered the fame appearances, but without being able to make any of the infecls ftir. 

 Difappointed and vexed at not being able to fee them in motion with fun light, and recolltcling the 

 heat of the candle, he threw the concentrated rays of the fun upon them with a burning-glafs, which 

 completely anfwered his purpofe of putting them in motion, and fhcwing them in every different 

 point of view. To defcribe minutely an infect fo fmall as not to be diftinguiftiable by the naked 

 eye, would, fays he, be no eafy matter; it is fufh cicnt to fay, that its general appearance is very fimi- 

 lar to the woodloufe, though infinitely fmaller. 



As foon as he was clearly ufcertaJKed of the exiftence of this infect, his mind was, he fays, per 

 fectly at cafe with regard to the caufe of the diftemper; but though he could very readily conceive 

 that vermin, in the early ftages of the growth of a plant, might fo injure the ftamina as to render it 

 unfit to produce any thing but fmut, he could not fo well underitand how it was poffible for the 

 mere touch of the black earth contained in the fmut-balls to produce the fame effect. 



After fome reasoning he, however, gives it as his opinion that fmut is occafioned by the fmall in 



FG 



