546    Plant  Groups,  their  Constituents  and  Properties.  {Am^oZ'mo&im' 
the  causes  of  scarcity  in  the  supply  of  senna  and  gum  arabic  ;  to  the 
political  complications  which  were  engendered  by  the  cultivation  of 
opium ;  to  the  introduction  into  medical  use  of  cinchona  bark  ;  to 
the  changes  in  commerce  and  manufacture,  as  well  as  in  pharmacy 
and  medicine,  which  are  the  direct  outcome  of  the  cultivation  of  the 
cinchonas  in  the  Eastern  hemisphere. 
The  investigations  in  Materia  Medica  have  supplied  the  infant 
Chemistry  with  a  multitude  of  valuable  facts,  and  helped  to  nourish 
that  science,  until  it  is  now  able  to  repay  the  debt  by  furnishing, 
from  its  own  retorts,  many  compounds  which  may  take,  and  to 
some  extent  do  take,  the  place  of  medicines  that  heretofore  were 
procured  only  from  Nature's  bountiful  laboratory. 
Medicine,  that  is,  Materia  Medica,  was  to  a  large  extent  the 
incentive  that  led  to  the  study  of  Botany ;  and  that  science,  in  turn, 
again  leads  to  the  study  of  the  possible  uses  of  plants,  or  to  economic 
and  medical  botany.  That,  apparently,  a  certain  relation  exists 
between  the  genetic  forms  or  groups  of  plants  and  their  properties, 
useful  as  well  as  deleterious,  was  pointed  out  more  than  a  century 
ago,  after  Linne  had  laid  the  foundation  for  the  scientific  classifica- 
tion of  plants.  Though  subsequently  repeatedly  denied,  such  a 
relation  has,  in  more  recent  times,  been  unquestionably  established 
and  will  doubtless  become  still  more  apparent,  as  continued 
researches  make  us  more  intimately  acquainted  with  the  internal 
structure  of  a  larger  number  of  plants,  and  with  the  influence  which 
the  various  kinds  of  tissue  exert  upon  the  elaboration  of  the  crude 
material  taken  up  from  the  soil  or  imbibed  from  the  atmosphere. 
The  connection  alluded  to  is  entirely  different  from  that  which  in  all 
countries  the  popular  mind  has  attributed  as  existing  between  the 
external  shape  of  a  plant  or  a  plant-part  and  its  curative  effects. 
The  traditions  of  such  apparent  exemplification  of  the  inherent 
property  by  visible  and  striking  characters  are  still  cherished  in 
many  localities  among  different  people,  and  find  expression  in 
popular  names  as  well  as  in  medical  and  botanical  terms.  The 
peculiar  shape  of  the  three-lobed  leaves  of  a  ranunculaceous  plant, 
and  of  the  lobed  green  and  brown  thallus  of  certain  acotyledons,  in 
which  a  resemblance  to  the  liver  was  fancied,  induced  the  belief 
into  their  value  for  the  cure  of  liver  complaints ;  hence  the  appella- 
tions hepatica,  and  liverwort,  and  equivalent  designations  in  other 
languages.    The  Latin  cardiaca  and  synonymous  terms  in  French 
