﻿308 
  Retrograde 
  Varieties 
  

  

  do 
  so 
  in 
  nearly 
  all 
  the 
  crosses 
  made 
  for 
  prac- 
  

   tical 
  purposes, 
  and 
  in 
  very 
  many 
  scientific 
  ex- 
  

   periments. 
  Even 
  Mendel's 
  peas 
  were 
  not 
  pure 
  

   in 
  this 
  respect, 
  much 
  less 
  do 
  the 
  campions 
  noted 
  

   above 
  differ 
  only 
  in 
  Mendelian 
  characters. 
  

  

  Comparative 
  and 
  systematic 
  studies 
  must 
  be 
  

   made 
  to 
  ascertain 
  the 
  true 
  nature 
  of 
  every 
  unit 
  

   in 
  every 
  single 
  plant, 
  and 
  crossing 
  experiments 
  

   must 
  be 
  based 
  on 
  these 
  distinctions 
  in 
  order 
  to 
  

   decide 
  what 
  laws 
  are 
  applicable 
  in 
  any 
  case. 
  

  

  