﻿12 
  Descent 
  

  

  In 
  order 
  to 
  meet 
  this 
  difficulty 
  we 
  must 
  recog- 
  

   nize 
  two 
  sorts 
  of 
  species. 
  The 
  systematic 
  spe- 
  

   cies 
  are 
  the 
  practical 
  units 
  of 
  the 
  systematists 
  

   and 
  florists, 
  and 
  all 
  friends 
  of 
  wild 
  nature 
  

   should 
  do 
  their 
  utmost 
  to 
  preserve 
  them 
  as 
  

   Linnaeus 
  has 
  proposed 
  them. 
  These 
  units 
  how- 
  

   ever, 
  are 
  not 
  really 
  existing 
  entities; 
  they 
  

   have 
  as 
  little 
  claim 
  to 
  be 
  regarded 
  as 
  such 
  

   as 
  genera 
  and 
  families. 
  The 
  real 
  units 
  are 
  

   the 
  elementary 
  species; 
  their 
  limits 
  often 
  ap- 
  

   parently 
  overlap 
  and 
  can 
  only 
  in 
  rare 
  cases 
  be 
  

   determined 
  on 
  the 
  sole 
  ground 
  of 
  field-obser- 
  

   vations. 
  Pedigree-culture 
  is 
  the 
  method 
  re- 
  

   quired 
  and 
  any 
  form 
  which 
  remains 
  constant 
  

   and 
  distinct 
  from 
  its 
  allies 
  in 
  the 
  garden 
  is 
  to 
  

   be 
  considered 
  as 
  an 
  elementary 
  species. 
  

  

  In 
  the 
  following 
  lectures 
  we 
  shall 
  con- 
  

   sider 
  this 
  point 
  at 
  length, 
  to 
  show 
  the 
  compound 
  

   nature 
  of 
  systematic 
  species 
  in 
  wild 
  and 
  in 
  culti- 
  

   vated 
  plants. 
  In 
  both 
  cases, 
  the 
  principle 
  is 
  

   becoming 
  of 
  great 
  importance, 
  and 
  many 
  pa- 
  

   pers 
  published 
  recently 
  indicate 
  its 
  almost 
  uni- 
  

   versal 
  acceptation. 
  

  

  Among 
  the 
  systematic 
  subdivisions 
  of 
  species, 
  

   not 
  all 
  have 
  the 
  same 
  claim 
  to 
  the 
  title 
  of 
  ele- 
  

   mentary 
  species. 
  In 
  the 
  first 
  place 
  the 
  cases 
  

   in 
  which 
  the 
  differences 
  may 
  occur 
  between 
  

   parts 
  of 
  the 
  same 
  individual 
  are 
  to 
  be 
  excluded. 
  

   Dividing 
  an 
  alpine 
  plant 
  into 
  two 
  halves 
  and 
  

  

  