﻿Balanced 
  Crosses 
  307 
  

  

  True 
  elementary 
  species 
  differ 
  from 
  each 
  

   other 
  in 
  a 
  number 
  of 
  unit-characters, 
  which 
  do 
  

   not 
  contrast. 
  They 
  have 
  arisen 
  by 
  progressive 
  

   mutation. 
  One 
  species 
  has 
  one 
  kind 
  of 
  unit, 
  

   another 
  species 
  has 
  another 
  kind. 
  On 
  com- 
  

   bining 
  these, 
  there 
  can 
  be 
  no 
  interchange. 
  

   Mendelism 
  assumes 
  such 
  an 
  interchange 
  be- 
  

   tween 
  units 
  of 
  the 
  same 
  character, 
  but 
  in 
  a 
  

   different 
  condition. 
  Activity 
  and 
  latency 
  are 
  

   such 
  conditions, 
  and 
  therefore 
  Mendel's 
  law 
  

   obviously 
  applies 
  to 
  them. 
  They 
  require 
  pairs 
  

   of 
  antagonistic 
  qualities, 
  and 
  have 
  no 
  connec- 
  

   tion 
  whatever 
  with 
  those 
  qualities 
  which 
  do 
  not 
  

   find 
  an 
  opponent 
  in 
  the 
  other 
  parent. 
  Now, 
  

   only 
  pure 
  varieties 
  afford 
  such 
  pure 
  conditions. 
  

   When 
  undergoing 
  further 
  modifications, 
  some 
  

   of 
  them 
  may 
  be 
  in 
  the 
  progressive 
  line 
  and 
  

   others 
  in 
  the 
  retrogressive. 
  Progressive 
  modi- 
  

   fications 
  give 
  new 
  units, 
  which 
  are 
  not 
  in 
  con- 
  

   trast 
  with 
  any 
  other, 
  retrograde 
  changes 
  turn 
  

   active 
  units 
  into 
  the 
  latent 
  condition 
  and 
  so 
  give 
  

   rise 
  to 
  pairs. 
  Ordinary 
  species 
  generally 
  

   originate 
  in 
  this 
  way, 
  and 
  hence 
  differ 
  from 
  

   each 
  other 
  partly 
  in 
  specific, 
  partly 
  in 
  varietal 
  

   characters. 
  As 
  to 
  the 
  first, 
  they 
  give 
  in 
  their 
  

   hybrids 
  stable 
  peculiarities, 
  while 
  as 
  to 
  the 
  

   latter, 
  they 
  split 
  up 
  according 
  to 
  Mendel's 
  law. 
  

  

  Unpaired 
  or 
  unbalanced 
  characters 
  lie 
  side 
  by 
  

   side 
  with 
  paired 
  or 
  balanced 
  qualities, 
  and 
  they 
  

  

  