Pedigree  Seed  Corn. 
127 
earlier,  either  in  respect  of  the  characters  of  the  grain,  or  of 
prolificacy,  or  any  other  racial  character. 
We  may  now  briefiy  consider  the  effects  likely  to  be 
produced  by  natural  selection  in  the  case  of  mixed  races,  pure 
races,  and  hybrid  races  of  cereals  respectively. 
Take  first  the  case  of  a mixed  race  introduced  into  and 
grown  on  for  several  years  in  a particular  locality  and  under 
approximately  similar  conditions  from  year  to  year  without 
further  admixture.  One  or  more  of  the  types  of  which  the 
aggregate  is  composed  will  probably  be  better  suited  than  the 
others  and  survive  under  the  average  conditions,  and,  with 
three  out  of  the  four  of  the  seeds  sown  in  each  year  failing  to 
repioduce  grain,  there  may  accrue  a considerable  difference  in 
the  character  of  the  aggiegate  even  within  a few  years,  whilst 
after  several  years  the  aggregate  may  be  of  quite  a different 
racial  character  to  the  original  bulk.  The  general  tendency, 
however,  would  be  towards  homogeneity  in  consequence  of 
some  types  disappearing. 
Let  a stock  of  this  modified  aggregate  be  transferred  to 
another  district  with  quite  different  soil,  climatic  and  cultural 
conditions  ; then  if  there  is  left  out  of  consideration  for  the 
moment  the  immediate  effect  due  directly  to  change  of  locality, 
the  particular  race  or  races  which  have  best  survived  the 
previous  conditions,  and  which  make  up  the  greater  part  of 
the  aggregate,  may  or  may  not  be  better  suited  to  the  new 
conditions  than  some  which  have  nearly  died  out,  and  after 
a few  years  the  new  conditions  may  remould  the  racial 
characters  of  the  aggregate  either  in  the  direction  of  greater 
homogeneity,  or  at  first  (if  only  the  smaller  proportion  of  the 
aggregate  in  that  best  suited  to  the  new  conditions)  towards 
greater  heterogeneity.  Ultimately,  however,  the  tendency  will 
be  again  towards  a more  or  less  homogeneous  aggregate,  differing 
however,  probably  in  general  character,  both  from  the  original 
and  from  the  transferred  aggregates.  All  this  agrees  with  the 
observed  fact  that  a “ change  of  seed  ” sometimes  gives  good 
results  at  once,  sometimes  after  a year  or  two,  and  sometimes 
not  at  all. 
Consider  now  the  case  of  a “ pure  race  ” — the  progeny  of 
an  individual  plant — introduced  into  cultivation  in  a particular 
locality.  So  long  as  this  stock  is  kept  free  from  admixture 
and  neglecting  “ sports,”  and  also  accidental  cross-fertilisation, 
both  of  which  are  very  rare  with  wheat,  barley,  and  oats,  the 
aggregate  will  remain  homogeneous.  The  yield  and  quality 
will  of  course  vary  from  year  to  year,  but  such  crowding 
out  of  individuals  as  takes  place  will  not  affect  the  racial 
characters,  and  it  is  obvious  that  if  these  are  constant,  the 
question  whether  this  particular  race  is  suited  to  the  average 
