EFFECTS  OF  SOIL,  ETC.  ON  ACTIVE  PRINCIPLES  OF  PLANTS.  49 
pie  of  rotation,  but  the  most  experienced  prefer  supplying  their 
land  with  rich  stable  manure  after  each  crop.  The  principle 
of  rotation  is  ultimately  exhaustive,  but  by  a  judicious  combi- 
nation of  both  principles  better  crops  are  obtained,  both  in 
quantity  and  quality. 
Plants  which  are  disposed  to  hybridity  should  be  frequently 
renewed  from  the  seeds  of  the  wild  plant ;  in  general,  the  ap- 
pearance of  medicinal  plants  under  cultivation,  as  far  as  my  op- 
portunities have  extended,  show  a  decided  absence  of  hybrid 
species.  This,  I  think,  is  produced  by  selecting  for  propaga- 
tion those  plants  which  are  symmetrical  in  tbeir  physical  and 
botanical  development. 
I  have  been  informed  that  the  parings  of  horses'  hoofs  is,  or 
was,  extensively  used  at  Mitcham  for  lavender  and  peppermint 
crops,  and  although  they  certainly  contain  a  considerable  quan- 
tity of  phosphate  of  lime  and  nitrogenized  matter,  it  is  difficult 
to  understand  their  suitability  as  a  manure,  unless,  from  their 
slow  and  gradual  decomposition,  the  soil  is  kept  in  a  more 
uniform  condition  for  a  much  longer  time.  I  have  not  been 
able  to  determine  the  absolute  value  of  this  dressing  for  oil- 
yielding  crops,  but  as  far  as  its  application  for  producing  laven- 
der flowers  for  bunching,"  it  seems  eminently  suited.  The 
grower  who  used  this  to  the  greatest  extent  did  not  cultivate 
lavender  for  distillation. 
It  has  been  stated  that  henbane  and  foxglove  lose  their  ac- 
tivity by  drying,  in  consequence  of  a  reduction  of  their  active 
principle.  This  I  am  not  able  to  support.  I  find  that  their 
active  principles,  as  well  as  those  of  many  other  plants,  are 
rendered  less  soluble,  from  a  modified  state  of  combination 
being  produced. 
By  imperfect  drying,  fermentation  might  arise  which  might 
alter  the  remedial  value  of  any  preparation  from  these  plants  ; 
but  experiments  are  still  wanting  to  prove  that  active  princi- 
ples are  capable  of  conversion  by  direct  fermentation,  or  decay, 
and  toxicologists  assure  us  that  organized  structures  are  not 
able  to  transform  into  other  compounds  the  elements  which 
form  the  molecule  of  an  alkaloid. 
4 
