﻿778 
  Fluctuations 
  

  

  selection 
  is 
  not 
  limited 
  to 
  a 
  single 
  choice, 
  but 
  

   may 
  be 
  applied 
  in 
  two 
  or 
  more 
  succeeding 
  gen- 
  

   erations. 
  Obviously 
  such 
  a 
  repetition 
  affords 
  

   a 
  better 
  chance 
  of 
  increasing 
  the 
  progression 
  of 
  

   the 
  average 
  and 
  of 
  ameliorating 
  the 
  race 
  to 
  a 
  

   greater 
  degree 
  than 
  would 
  be 
  possible 
  by 
  a 
  sin- 
  

   gle 
  choice. 
  This 
  principle 
  of 
  repeated 
  selection 
  

   is 
  at 
  present 
  the 
  prominent 
  feature 
  of 
  race- 
  

   improvement. 
  Next 
  to 
  variety-testing 
  and 
  

   hybridizing 
  it 
  is 
  the 
  great 
  source 
  of 
  the 
  steady 
  

   progression 
  of 
  agricultural 
  crops. 
  From 
  a 
  

   practical 
  standpoint 
  the 
  method 
  is 
  clear 
  and 
  as 
  

   perfect 
  as 
  might 
  be 
  expected, 
  but 
  this 
  is 
  not 
  the 
  

   side 
  of 
  the 
  problem 
  with 
  which 
  we 
  are 
  concerned 
  

   here. 
  The 
  theoretical 
  analysis 
  and 
  explana- 
  

   tion 
  of 
  the 
  results 
  obtained, 
  however, 
  is 
  sub- 
  

   ject 
  to 
  much 
  doubt, 
  and 
  to 
  a 
  great 
  divergence 
  

   of 
  conceptions. 
  So 
  it 
  is 
  also 
  with 
  the 
  applica- 
  

   tion 
  of 
  the 
  practical 
  processes 
  to 
  those 
  occur- 
  

   ring 
  in 
  nature. 
  Some 
  assume 
  that 
  here 
  repeated 
  

   selection 
  is 
  only 
  of 
  subordinate 
  importance, 
  

   while 
  others 
  declare 
  that 
  the 
  whole 
  process 
  of 
  

   evolution 
  is 
  due 
  to 
  this 
  agency. 
  This 
  very 
  im- 
  

   portant 
  point 
  however, 
  will 
  be 
  reserved 
  for 
  the 
  

   next 
  lecture, 
  and 
  only 
  the 
  facts 
  available 
  at 
  pres- 
  

   ent 
  will 
  be 
  considered 
  here. 
  

  

  As 
  a 
  first 
  example 
  we 
  may 
  take 
  the 
  ray-florets 
  

   of 
  the 
  composites. 
  On 
  a 
  former 
  occasion 
  we 
  

   have 
  dealt 
  with 
  their 
  fluctuation 
  in 
  number 
  and 
  

  

  