﻿242 
  Retrograde 
  Varieties 
  

  

  flowers, 
  which 
  are 
  not 
  liable 
  to 
  produce 
  yellow 
  

   variations, 
  as 
  in 
  Salvia, 
  Aster, 
  Centaurea, 
  

   Vinca, 
  Polygala 
  and 
  many 
  others. 
  Even 
  the 
  

   rare 
  pale 
  yellowish 
  species 
  of 
  some 
  of 
  these 
  

   genera 
  have 
  no 
  tendency 
  in 
  this 
  direction. 
  The 
  

   hyacinths 
  are 
  the 
  most 
  remarkable, 
  if 
  not 
  the 
  

   sole 
  known 
  instance 
  of 
  a 
  species 
  having 
  red 
  and 
  

   blue 
  and 
  white 
  and 
  yellow 
  varieties, 
  but 
  here 
  the 
  

   yellow 
  is 
  not 
  the 
  bright 
  golden 
  color 
  of 
  the 
  but- 
  

   tercups. 
  

  

  The 
  existence 
  of 
  varietal 
  colors 
  in 
  allied 
  spe- 
  

   cies 
  obviously 
  points 
  to 
  a 
  common 
  cause, 
  and 
  

   this 
  cause 
  can 
  be 
  no 
  other 
  than 
  the 
  latency 
  of 
  

   the 
  pigment 
  in 
  the 
  species 
  that 
  do 
  not 
  show 
  it. 
  

  

  The 
  conception 
  of 
  latency 
  of 
  characters 
  as 
  the 
  

   common 
  source 
  of 
  the 
  origination 
  of 
  varieties, 
  

   either 
  in 
  the 
  positive 
  or 
  in 
  the 
  negative 
  way, 
  

   leads 
  to 
  some 
  rules 
  on 
  variability, 
  which 
  are 
  

   known 
  under 
  the 
  names 
  given 
  to 
  them 
  by 
  Dar- 
  

   win. 
  They 
  are 
  the 
  rules 
  of 
  repeated, 
  homolog- 
  

   ous, 
  parallel 
  and 
  analogous 
  variability. 
  Each 
  

   of 
  them 
  is 
  quite 
  general, 
  and 
  may 
  be 
  recog- 
  

   nized 
  in 
  instances 
  from 
  the 
  most 
  widely 
  dis- 
  

   tant 
  families. 
  Each 
  of 
  them 
  is 
  quite 
  evident 
  

   and 
  easily 
  understood 
  on 
  the 
  principle 
  of 
  

   latency. 
  

  

  By 
  the 
  term 
  of 
  repeated 
  variability 
  is 
  meant 
  

   the 
  well-known 
  phenomenon, 
  that 
  the 
  same 
  va- 
  

   riety 
  has 
  sprung 
  at 
  different 
  times 
  and 
  in 
  dif- 
  

  

  