﻿294 
  Retrograde 
  Varieties 
  

  

  ity. 
  Read 
  in 
  the 
  light 
  of 
  modern 
  ideas 
  on 
  unit- 
  

   characters 
  it 
  is 
  now 
  one 
  of 
  the 
  most 
  important 
  

   works 
  on 
  heredity 
  and 
  has 
  already 
  widespread 
  

   and 
  abiding 
  influence 
  on 
  the 
  philosophy 
  of 
  hy- 
  

   bridism 
  in 
  general. 
  

  

  But 
  from 
  its 
  very 
  nature 
  and 
  from 
  the 
  choice 
  

   of 
  the 
  material 
  made 
  by 
  Mendel, 
  it 
  is 
  restricted 
  

   to 
  balanced 
  or 
  varietal 
  crosses. 
  It 
  assumes 
  

   pairs 
  of 
  characters 
  and 
  calls 
  the 
  active 
  unit 
  of 
  

   the 
  pair 
  dominant, 
  and 
  the 
  latent 
  recessive, 
  

   without 
  further 
  investigations 
  of 
  the 
  question 
  

   of 
  latency. 
  It 
  was 
  worked 
  out 
  by 
  Mendel 
  for 
  a 
  

   large 
  group 
  of 
  varieties 
  of 
  peas, 
  but 
  it 
  holds 
  

   good, 
  with 
  only 
  apparent 
  exceptions, 
  for 
  a 
  wide 
  

   range 
  of 
  cases 
  of 
  crosses 
  of 
  varietal 
  characters. 
  

   Recently 
  many 
  instances 
  have 
  been 
  tested, 
  and 
  

   even 
  in 
  many 
  cases 
  third 
  and 
  later 
  generations 
  

   have 
  been 
  counted, 
  and 
  whenever 
  the 
  evidence 
  

   was 
  complete 
  enough 
  to 
  be 
  trusted, 
  Mendel's 
  

   prophecy 
  has 
  been 
  found 
  to 
  be 
  right. 
  

  

  According 
  to 
  this 
  law 
  of 
  Mendel's 
  the 
  pairs 
  

   of 
  antagonistic 
  characters 
  in 
  the 
  hybrid 
  split 
  up 
  

   in 
  their 
  progeny, 
  some 
  individuals 
  reverting 
  to 
  

   the 
  pure 
  parental 
  types, 
  some 
  crossing 
  with 
  

   each 
  other 
  anew, 
  and 
  so 
  giving 
  rise 
  to 
  a 
  new 
  

   generation 
  of 
  hybrids. 
  Mendel 
  has 
  given 
  a 
  

   very 
  suggestive 
  and 
  simple 
  explanation 
  of 
  his 
  

   formula. 
  Putting 
  this 
  in 
  the 
  terminology 
  of 
  

   to-day, 
  and 
  limiting 
  it 
  to 
  the 
  occurrence 
  of 
  only 
  

  

  