336 



ON THE CULTURE 



fected plants with snuff or tobacco-dust. 3. By a 

 decoction or infusion of tobacco. The manner 

 and application of all these will be hereafter con- 

 sidered. 



2. The Acarus 5 , commonly called the Red 

 Spider. This is a pest to almost every kind of 

 plant, for this insect is not only exceedingly per- 

 nicious to most plants kept under glass, but is also 

 very prejudicial to many growing in the open air, 

 particularly to some kinds of fruit-trees when 

 trained against walls : as for instance, the cherry, 

 plumb, apricot, and peach. When the Vine 

 grows under glass, it is very liable to be greatly 

 infested with this pernicious species, but I never 

 knew the Acari attack it in the open air. 



In hot dry weather the increase of these insects 

 is exceedingly rapid, and when they become nume- 

 rous, they, by various means, soon make great 



b The Acarus is of the Order Aptera. 

 Its Characters are : 

 Two eyes placed on the sides of the head remote from one 

 another. 



Its mouth or proboscis is formed by a small-pointed rostrum 

 inclosed in a sheath. 



The antennae are shorter than the proboscis, and said to be 

 articulated, and made like feet. 



The head of the same size, and united to the thorax. 



The Acarus has eight feet, made for running. 



There are many species of this genus : some live upon other 

 animals, quadrupeds, birds, and insects; some of the last- 

 mentioned class are often quite covered with them ; others of 

 them live in the water ; others upon trees, plants, &c. They 

 are oviparous, v 



