﻿Experimental 
  Pedigree-Cultures 
  565 
  

  

  considered 
  to 
  constitute 
  only 
  retrograde 
  steps, 
  

   and 
  no 
  advance. 
  This 
  conclusion 
  has 
  been 
  fully 
  

   justified 
  by 
  some 
  crossing 
  experiments 
  with 
  

   brevistylis, 
  which 
  wholly 
  complies 
  with 
  Men- 
  

   del's 
  law, 
  and 
  in 
  one 
  instance 
  with 
  nanella, 
  

   which 
  behaves 
  in 
  the 
  same 
  manner, 
  if 
  crossed 
  

   with 
  rubrinervis. 
  

  

  On 
  the 
  other 
  hand, 
  gigas 
  and 
  rubrinervis, 
  ob- 
  

   longa 
  and 
  albida 
  obviously 
  bear 
  the 
  characters 
  

   of 
  progressive 
  elementary 
  species. 
  They 
  are 
  

   not 
  differentiated 
  from 
  lamarcklana 
  by 
  one 
  or 
  

   two 
  main 
  features. 
  They 
  diverge 
  from 
  it 
  in 
  

   nearly 
  all 
  organs, 
  and 
  in 
  all 
  in 
  a 
  definite 
  though 
  

   small 
  degree. 
  They 
  may 
  be 
  recognized 
  as 
  soon 
  

   as 
  they 
  have 
  developed 
  their 
  first 
  leaves 
  and 
  re- 
  

   main 
  discernible 
  throughout 
  life. 
  Their 
  char- 
  

   acters 
  refer 
  chiefly 
  to 
  the 
  foliage, 
  but 
  no 
  less 
  to 
  

   the 
  stature, 
  and 
  even 
  the 
  seeds 
  have 
  peculiari- 
  

   ties. 
  There 
  can 
  be 
  little 
  doubt 
  but 
  that 
  all 
  the 
  

   attributes 
  of 
  every 
  new 
  species 
  are 
  derived 
  from 
  

   one 
  principal 
  change. 
  But 
  why 
  this 
  should 
  af- 
  

   fect 
  the 
  foliage 
  in 
  one 
  manner, 
  the 
  flowers 
  in 
  

   another 
  and 
  the 
  fruits 
  in 
  a 
  third 
  direction, 
  re- 
  

   mains 
  obscure. 
  To 
  gain 
  ever 
  so 
  little 
  an 
  insight 
  

   into 
  the 
  nature 
  of 
  these 
  changes, 
  we 
  may 
  best 
  

   compare 
  the 
  differences 
  of 
  our 
  evening-prim- 
  

   roses 
  with 
  those 
  between 
  the 
  two 
  hundred 
  ele- 
  

   mentary 
  species 
  of 
  Draba 
  and 
  other 
  similar 
  

   instances. 
  In 
  doing 
  so 
  we 
  find 
  the 
  same 
  main 
  

  

  