﻿Inconstancy 
  of 
  Improved 
  Races 
  791 
  

  

  of 
  selection 
  here 
  finds 
  its 
  limit 
  and 
  that 
  cen- 
  

   turies 
  and 
  perhaps 
  geologic 
  periods 
  of 
  contin- 
  

   ued 
  effort 
  in 
  the 
  same 
  direction 
  are 
  not 
  capable 
  

   of 
  adding 
  anything 
  more 
  to 
  the 
  initial 
  effect. 
  

   Some 
  illustrative 
  examples 
  may 
  suffice 
  to 
  

   prove 
  the 
  validity 
  of 
  this 
  assertion. 
  Every 
  bot- 
  

   anist 
  who 
  has 
  studied 
  the 
  agricultural 
  practice 
  

   of 
  plant-breeding, 
  or 
  the 
  causes 
  of 
  the 
  geo- 
  

   graphic 
  distribution 
  of 
  plants, 
  will 
  easily 
  recall 
  

   to 
  his 
  mind 
  numerous 
  similar 
  cases. 
  Perhaps 
  

   the 
  most 
  striking 
  instance 
  is 
  afforded 
  by 
  culti- 
  

   vated 
  biennial 
  plants. 
  The 
  most 
  important 
  of 
  

   them 
  are 
  forage-beets 
  and 
  sugar-beets. 
  They 
  

   are, 
  of 
  course, 
  cultivated 
  only 
  as 
  biennials, 
  

   but 
  some 
  annual 
  specimens 
  may 
  be 
  seen 
  each 
  

   year 
  and 
  in 
  nearly 
  every 
  field. 
  They 
  arise 
  

   from 
  the 
  same 
  seed 
  as 
  the 
  normal 
  individuals, 
  . 
  

   and 
  their 
  number 
  is 
  obviously 
  dependent 
  on 
  

   external 
  conditions, 
  and 
  especially 
  on 
  the 
  time 
  

   of 
  sowing. 
  Ordinary 
  cultures 
  often 
  show 
  as 
  

   much 
  as 
  \% 
  of 
  these 
  useless 
  plants, 
  but 
  the 
  exi- 
  

   gencies 
  of 
  time 
  and 
  available 
  labor 
  often 
  com- 
  

   pel 
  the 
  cultivator 
  to 
  have 
  a 
  large 
  part 
  of 
  his 
  

   fields 
  sown 
  before 
  spring. 
  In 
  central 
  Eu- 
  

   rope, 
  where 
  the 
  climate 
  is 
  unfavorable 
  at 
  this 
  

   season, 
  the 
  beets 
  respond 
  by 
  the 
  production 
  of 
  

   far 
  larger 
  proportions 
  of 
  annual 
  specimens, 
  

   their 
  number 
  coming 
  often 
  up 
  to 
  20$ 
  or 
  more, 
  

   thus 
  constituting 
  noticeable 
  losses 
  in 
  the 
  prod- 
  

  

  