ON  THE  DESTRUCTION  OF  NOXIOUS  INSECTS. 
69 
the  dried  flower-heads,  gathered  when  ripe,  on  fine  days,  and 
usually  dried  by  exposure  to  the  sun  ;  but  they  have  been  found 
to  be  more  serviceable  when  dried  in  the  shade,  during  which 
operation  they  are  occasionally  turned.  In  the  process  of  des- 
iccation they  lose  about  90  per  cent.  When  perfectly  dried, 
they  are  first  comminuted  with  the  hand,  and  then  reduced  to 
powder  in  a  small  mill. 
A  quantity  of  these  plants  grown  upon  eighteen  square  rods 
is  estimated  to  furnish  one  hundred  pounds  of  powder,  which  is 
best  preserved  in  sealed  vessels  of  glass.  The  application  is 
made  either  as  a  powder  or  as  an  infusion,  though  in  the  latter 
form  it  is  more  beneficial,  especially  when  intended  for  the  de- 
struction of  insects  on  plants.  The  powder  may  be  employed 
directly  to  the  insects  themselves,  or  in  the  places  which  they 
frequent.  They  are  attracted  by  its  smell,  become  stupefied, 
and  immediately  die.  This  substance  may  be  employed  without 
injury  to  the  larger  animals,  or  to  man.  It  is  intimated  that 
the  amount  of  this  powder  consumed  annually  in  Russia  alone 
is  about  500  tons. 
The  inhabitants  of  the  Caucasus  and  adjoining  countries  who 
used  these  powders  had  only  a  very  limited  knowledge  of  their 
plants,  and  did  not  suspect  that  one  among  them,  the  Pyre- 
thrum  Willemoti,  Duchartre,  would  be  called  upon  to  render  the 
most  effective  service  to  agriculture  and  horticulture,  achieving 
the  preservation  of  food,  wool,  furs,  and  the  comfort  of  man 
and  the  domestic  animals,  etc. 
These  powders  had  been  introduced  into  France  for  several 
years  before  a  choice  had  been  made  among  them,  and  the  spe- 
cial importance  of  this  particular  species  recognized.  The  high 
price,  and  the  numerous  adulterations  they  have  undergone,  di- 
verted the  public  from  this  acquisition,  and  from  a  public  appre- 
ciation of  its  efficacy.  Submitted  to  a  close  analysis,  these 
powders,  as  sold,  have  been  found  to  be  mixed  with  dangerous 
substances,  which  in  due  regard  to  public  safety  require  to  be 
vigorously  excluded  from  sale.  In  them  sumac  powder  is  a  com- 
mon ingredient,  from  its  close  resemblance  to  the  Pyrethrum 
powder ;  and  also  Jalap,  cockle  of  Levant,  nux  vomica,  and 
even  arsenic,  enter  into  the  composition  of  the  powders  we  have 
examined. 
