According  to  our  theory,  the  transmission  of  a  variation  by
seeds  depends  on  the  presence  of  a  corresponding  modification
in  the  majority  of  the  determinants  in  the  germ-plasm  of  the
seeds.  If  the  germ-plasm  contains  a  hundred  ids,  the  con-
trolling forces  of  which  are  equal,-  more  than  fifty  determinants
N  must  be  transformed  into  N^  before  the  modification  would
be  perceptible  in  the  seedling.  Since  therefore,  as  was  re-
marked above,  new  variations  probably  never  appear  simultane-
ously in  all  the  determinants,  but  only  in  a  varying  percentage
of  the  ids,  the  chances  are  greatly  against  all  the  seedlings
produced  by  the  transformed  plant  exhibiting  this  modification.
For  every  germ-cell  has  undergone  a  *  reducing  division,'  and
hence  many  of  them  will  always  only  possess  a  minority  of  the
modified  determinants  N^,  and  this  may  even  be  a  very  small
one  if  the  majority  in  the  germ-plasm  of  the  parent-plant  was
small.  When  two  such  cells  unite  in  the  process  of  amphimixis,
the  resulting  germ-plasm  contains  only  a  small  minority  of
modified  determinants  N^  and  the  modification  is  inappreciable.
This  accounts  for  the  fact  that  the  seedlings  of  a  variety  hardly
ever  reproduce  the  variety  in  all  cases;  and  that  in  rarer  in-
stances, such  as  that  of  the  weeping  oak  already  mentioned,
all  the  seedlings  may  exhibit  the  corresponding  variation,  al-
though in  varying  degrees.  For  the  composition  of  the  germ-
plasm  must  differ  in  each  of  them  in  consequence  of  the
processes  of  ^  reducing  division '  and  amphimixis,  even  when  the
parent-plant  contains  only  a  small  but  ever  varying  minority  of
ancestral  determinants.
