66  ON  THE  DESTRUCTION  OF  NOXIOUS  INSECTS. 
ON  THE  DESTRUCTION  OF  NOXIOUS  INSECTS  BY  MEANS 
OF  THE  PYRETHRUM. 
By  C.  Willemot. 
Of  all  substances  hitherto  proposed  for  the  destruction  of 
noxious  insects,  powders  have  been  found  the  only  ones  that 
can  be  used  to  advantage,  on  account  of  their  simple  and  easy 
method  of  application,  All  such  powders,  too,  which  have  been 
employed,  so  far  as  known,  are  derived  from  the  vegetable 
creation.  It  would  occupy  too  great  a  space  to  enumerate  here 
all  the  plants  used  in  a  form  of  powder  for  this  purpose  ;  it  will 
suffice  to  mention  some  which  have  been  more  particularly  un- 
der observation.  Among  these  are  the  straight-leaved  pepper- 
wort  [Lepidium  ruderale,  Linn.,  and  Thlaspi  ruderale,  Desfon.), 
found  growing  in  uncultivated  places  and  among  rubbish  around 
Paris.  This  is  used  in  Southern  Dalmatia,  in  the  form  of  pow- 
der, almost  exclusively  for  the  destruction  of  fleas.  In  some 
parts  of  Southern  Russia,  especially  in  the  Crimea,  a  plant  very 
common  in  France,  Aristoloehia  Clematitis,  Linn,  (common 
birthwort),  is  used  exclusively  to  destroy  bugs.  Sawdust  of 
aromatic  wood,  particularly  American  Cedar  {Cedrela  odorata, 
Linn.),  is  largely  sold  for  the  destruction  of  insects,  and,  ac- 
cording to  some  authorities,  most  of  the  powders  sold  in  Paris 
for  that  purpose  are  composed  of  that  substance.  But  after 
using  and  experimenting  with  them  we  have  been  fully  con- 
vinced that  the  object  cannot  thus  be  perfectly  attained.  Their 
action  is  feeble,  or  they  merely  stupefy  for  a  time  the  insect, 
which  soon  recovers  its  strength  and  sensibility  to  do  injury. 
The  greater  number  of  the  plants  which  furnish  the  most  sat- 
isfactory means  for  the  destruction  of  insects  are  of  the  genus 
Pyreihrum.  Many  observers,  considering  the  botanic  resem- 
blance (as  well  as  similar  properties  of  this-  genus)  with  kindred 
ones,  as  certain  chamomiles,  the  Anthemis  Cotula  for  instance, 
have  pretended  that  such  indigenous  plants  (chamomiles)  may 
specifically  furnish  a  powder  for  destroying  insects  equal  in 
every  respect  to  the  Pyreihrum,  But  accurate  and  detailed 
experiments  by  ourselves  and  other  competent  observers  refuse 
such  assertion.  Ail  the  efficacy  of  the  Anthemis  Cotula  con- 
sists in  rendering  the  insects  insensible  for  a  time,  instead  of 
