﻿Selection 
  of 
  Elementary 
  Species 
  99 
  

  

  In 
  order 
  to 
  get 
  a 
  closer 
  insight 
  into 
  the 
  

   causes 
  of 
  this 
  confused 
  condition 
  of 
  ordinary 
  

   races, 
  Rimpau 
  made 
  some 
  observations 
  on 
  

   Rivett's 
  wheat. 
  He 
  found 
  that 
  it 
  suffers 
  from 
  

   frost 
  during 
  winter 
  more 
  than 
  the 
  local 
  Ger- 
  

   man 
  varieties, 
  and 
  that 
  from 
  various 
  causes, 
  

   alien 
  seeds 
  may 
  accidentally, 
  and 
  not 
  rarely, 
  

   become 
  mixed 
  with 
  it. 
  The 
  threshing-machines 
  

   are 
  not 
  always 
  as 
  clean 
  as 
  they 
  should 
  be 
  and 
  

   may 
  be 
  the 
  cause 
  of 
  an 
  accidental 
  mixture. 
  

   The 
  manure 
  comes 
  from 
  stables, 
  where 
  straw 
  

   and 
  the 
  dust 
  from 
  many 
  varieties 
  are 
  thrown 
  

   together, 
  and 
  consequently 
  living 
  kernels 
  

   may 
  become 
  mixed 
  with 
  the 
  dung. 
  Such 
  stray 
  

   grains 
  will 
  easily 
  germinate 
  in 
  the 
  fields, 
  where 
  

   they 
  find 
  more 
  congenial 
  conditions 
  than 
  does 
  

   the 
  improved 
  variety. 
  If 
  winter 
  arrives 
  and 
  

   kills 
  quantities 
  of 
  this 
  latter, 
  the 
  accidental 
  local 
  

   races 
  will 
  find 
  ample 
  space 
  to 
  develop. 
  Once 
  

   started, 
  they 
  will 
  be 
  able 
  to 
  multiply 
  so 
  rapidly, 
  

   that 
  in 
  one 
  or 
  two 
  following 
  generations 
  they 
  

   will 
  constitute 
  a 
  very 
  considerable 
  portion 
  of 
  

   the 
  whole 
  harvest. 
  In 
  this 
  way 
  the 
  awnless 
  

   German 
  wheat 
  often 
  prevails 
  over 
  the 
  intro- 
  

   duced 
  English 
  variety, 
  if 
  the 
  latter 
  is 
  not 
  kept 
  

   pure 
  by 
  continuous 
  selection. 
  

  

  The 
  Swiss 
  wheat-breeder 
  Risler 
  made 
  an 
  ex- 
  

   periment 
  which 
  goes 
  to 
  prove 
  the 
  certainty 
  of 
  

   the 
  explanation 
  given 
  by 
  Rimpau. 
  He 
  ob- 
  

  

  