﻿20 
  Descent 
  

  

  local 
  adaptations 
  with 
  slight 
  changes 
  of 
  the 
  

   average 
  character 
  in 
  separate 
  localities, 
  seem 
  

   to 
  be 
  of 
  quite 
  normal 
  occurrence. 
  

  

  A 
  new 
  method 
  of 
  individual 
  selection 
  has 
  

   been 
  used 
  in 
  recent 
  years 
  in 
  America, 
  especially 
  

   by 
  W. 
  M. 
  Hays. 
  It 
  consists 
  in 
  judging 
  the 
  

   hereditary 
  worth 
  of 
  a 
  plant 
  by 
  the 
  average 
  con- 
  

   dition 
  of 
  its 
  offspring, 
  instead 
  of 
  by 
  its 
  own 
  

   visible 
  characters. 
  If 
  this 
  determination 
  of 
  the 
  

   11 
  centgener 
  power, 
  " 
  as 
  Hays 
  calls 
  it, 
  should 
  

   prove 
  to 
  be 
  the 
  true 
  principle 
  of 
  selection, 
  then 
  

   indeed 
  the 
  analogy 
  between 
  natural 
  and 
  artifi- 
  

   cial 
  selection 
  would 
  lose 
  a 
  large 
  part 
  of 
  its 
  im- 
  

   portance. 
  We 
  will 
  reserve 
  this 
  question 
  for 
  the 
  

   last 
  lecture, 
  as 
  it 
  pertains 
  more 
  to 
  the 
  future, 
  

   than 
  to 
  our 
  present 
  stock 
  of 
  knowledge. 
  

  

  Something 
  should 
  be 
  said 
  here 
  concerning 
  

   hybrids 
  and 
  hybridism. 
  This 
  problem 
  has 
  of 
  

   late 
  reached 
  such 
  large 
  proportions 
  that 
  it 
  can- 
  

   not 
  be 
  dealt 
  with 
  adequately 
  in 
  a 
  short 
  survey 
  

   of 
  the 
  phenomena 
  of 
  heredity 
  in 
  general. 
  It 
  

   requires 
  a 
  separate 
  treatment. 
  For 
  this 
  reason 
  

   I 
  shall 
  limit 
  myself 
  to 
  a 
  single 
  phase 
  of 
  the 
  prob- 
  

   lem, 
  which 
  seems 
  to 
  be 
  indispensable 
  for 
  a 
  true 
  

   and 
  at 
  the 
  same 
  time 
  easy 
  distinction 
  between 
  

   elementary 
  species 
  and 
  retrograde 
  varieties. 
  Ac- 
  

   cording 
  to 
  accepted 
  terminology, 
  some 
  crosses 
  

   are 
  to 
  be 
  considered 
  as 
  unsymmetrical, 
  while 
  

   others 
  are 
  symmetrical. 
  The 
  first 
  are 
  one-sided, 
  

  

  