EFFECTS  OF  SOIL,  ETC.  ON  ACTIVE  PRINCIPLES  OF  PLANTS.  47 
vented,  and  the  yield  of  oil  is  greater  in  the  latter  case ;  the 
same  remark  applies,  though  less  forcibly,  to  peppermint  and 
rosemary. 
The  injudicious  mutilation  of  lavender  plants,  explain  to 
some  extent  the  great  differences  in  the  yield  of  oil  obtained  by 
different  growers. 
Mutilation,  when  practised,  should  be  regulated  by  the  season 
and  exposure  of  the  plant. 
I  am  strongly  of  opinion  that  mutilation  is  not  confined  to 
the  Labiatae,  although  I  hesitate  to  include  the  result  as  arising 
from  mutilation,  rather  than  an  indication  of  hybrid  develop- 
ment ;  but  it  is  a  singular  fact,  that  henbane  plants,  when  cul- 
tivated, show  a  tendency  to  capitate  inflorescence,  whereas  the 
same  plants  (self-sown),  are  strongly  disposed  to  a  racemose 
arrangement  of  its  flowers,  and  in  this  case  an  enormous  yield 
of  flowers  is  produced  compared  with  the  quantity  of  leaves. 
The  cultivated  plants  indicate  more  or  less  an  axillary  inflores- 
cence, and  the  capitate  disposition  should  perhaps  be  regarded 
as  arising  from  an  abortive  development  of  the  stem. 
My  experiments  on  henbane  were  far  advanced  when  I  first 
observed  this,  as  it  was  only  after  flowering  that  I  distinguished 
any  difference  in  the  plants. 
In  the  case  of  plants,  when  the  unexpanded  flowers  are 
gathered,  as  roses,  it  would  be  very  desirable  to  determine 
whether  any  difference  exists  in  the  medicinal  value  of  the 
flowers  first  collected  during  the  season,  and  those  which  are 
gathered  near  the  end,  for  it  is  evident  that  this  imposes  no  less 
on  the  energies  of  the  plant,  than  mutilation  in  the  general  ac- 
ceptation of  its  principle,  and  I  hope  to  return  to  this  inquiry 
at  an  early  period,  to  determine  the  difference,  if  any,  which 
arises  through  the  gradual  though  unavoidable  exhaustion  of 
the  plant. 
I  have  performed  an  extensive  series  of  experiments  on  this 
point,  to  determine  whether  such  plants  as  belladonna,  foxglove, 
and  henbane  should  be  allowed  to  perfect  their  flowers  or  seeds 
before  the  leaves  are  collected  for  the  preparation  of  medicinal 
extracts.  I  find  that  the  amount  of  active  principles  contained 
in  the  leaves,  remains  the  same  both  before  and  immediately 
