ON  THE  DESTRUCTION  OP  NOXIOUS  INSECTS,  71 
it.  Every  five  or  six  days  the  watering  is  to  be  renewed  in  or- 
der to  facilitate  the  germination, 
At  the  end  of  about  thirty  or  forty  days  the  young  plants 
make  their  appearance,  and  as  soon  as  they  have  gained  strength 
enough  they  are  transplanted.  Three  months  after,  they  are 
transplanted  again  at  wider  distances,  according  to  their 
strength,  each  time  being  of  course  watered,  but  only  moder- 
ately. 
The  blossoming  commences  in  the  second  year  towards  the 
end  of  May,  and  continues  to  the  end  of  September.  Within 
that  period  the  heads  from  which  the  powder  is  made  must  be 
gathered.  The  most  favorable  time  for  gathering  seems  to  be 
when  the  heads  are  about  to  open, — that  is,  when  the  florets  of 
the  circumference  are  yet  standing  erect.  In  this  state  the  fe- 
cundation takes  place,  and  the  essential  oil  contained  in  the 
heads  has  reached  its  highest  state  of  developement.  The 
stalks  and  leaves,  through  having  the  properties  in  a  less  degree, 
may  be  used  also  for  making  powder,  but  they  must  be  mixed 
with  the  flowers  in  the  proportion  of  a  third  of  their  weight. 
The  powder  thus  obtained  will  perfectly  answer  the  destruction 
of  insects.  Toward  the  end  of  September,  at  which  time  the 
blossoming  has  ceased,  the  stalks  are  cut  at  about  four  inches 
from  the  ground.  As  the  flowers  are  cut  they  are  dried  in  a 
granary  or  shed,  great  care,  however,  being  taken  not  to  expose 
them  to  moisture  or  to  the  rays  of  the  sun.  When  completely 
dried  the  flowers  are  to  be  hermetically  closed  up  in  sacks,  so  as 
to  prevent  too  early  pulverization.  In  pulverizing  them  it  is 
better  not  to  take  a  larger  quantity  thar:  the  wants  of  the  mo- 
ment may  require.  The  volatilization,  which  is  of  course  more 
rapid  in  the  powdered  form  than  in  flowers,  will  thus  be  avoid- 
ed. It  has  been  suggested  that  the  drying  of  the  flowers  for 
making  the  powder  might  be  effected  on  sheet-iron  plates,  like 
tea-leaves  are  dried  in  China,  but  this  operation  is  most  injuri- 
ous to  the  plant,  dissipating  the  essential  oil. 
Pulverization — Among  the  numerous  methods  which  we  have 
tried  in  order  to  simplify  the  pulverization  of  the  dried  flowers, 
that  which  appears  the  best  is  to  pound  the  flowers  in  a  mortar. 
The  mortar  should  be  covered  with  a  piece  of  leather,  through 
which  the  pestle  moves,  adjusting  it  in  such  a  way  as  to  prevent 
