Mr. CuRTis's Ohfervatiohs on Aphides. 85 



was delivered of a young one. Many years before this experiment, 

 with a view to deftroy the Aphides which infefted a plant in my 

 green-houfe, I immerfed one evening the whole plant, together 

 with the pot in which it grew, in a tub of water. In the morning 

 I took out the plant, expedting with certainty to find every Aphis 

 dead ; but to my great furprife they' foon appeared alive and well : 

 and thus, in addition to the other extraordinary phaenomena at- 

 tendant on thefe infe6ls, we find that they are capable of refining 

 the efFeiSls of immerfion in water for a great length of time. When 

 taken from the plant on. which they feed, and kept underwater, 

 they do not furvivefo long;' their ilruggling in tliat cafe perhaps 

 exhaufts them fooner. This part of the fubjeifl might be puOied 

 much further : it is fufficient for our purpofe to have Ihown that 

 wet is not fo hurtful to them as is generally imagined. 

 ^.Though no mode ot deftroying Aphides will perhaps ever be de- 

 vifed on a large fcale in the open air by artificial means, we can 

 accomplifh it moft effeftually when they infeft plants in {loves, 

 green-houfes, and frames, or in any fituation in which we can en- 

 velop them for a certain time in clouds of fmoke. Powders or 

 liquids, however fatal to Aphides, muft ever be inetFcdtual, from the 

 trouble and difficulty of applying them fo that they ihall come in 

 contact with thofe infe6ls, fituated as they ufually are ; but in this 

 refpe£t fmoke has every advantage, it penetrates and pervades their 

 inmoft recefles. The fmoke of common vegetables, however power- 

 ful, is found to be inadequate to their defl:ru6lion, and hitherto no 

 other than that of tobacco is found to be effectual. That, judi- 

 cioufly applied, completely anfwers the purpofe,without injuring the 

 plant. It moftly happens in well managed houfcs that a few plants 

 only are Infefled with Aphides: in fuch a cafe, the fmoking of the 

 whole houfe is abufinei's of unneceflaryexpenfe and trouble; and wo 

 would recommend to perfoiis who have large colieclions to make ufr 

 4 o! 



