344 
MendeVs  Laws  of  Heredity. 
chaffed  parent  or  it  may  be  hardly  discernible.  Similarly,  one 
cross  between  a hooded  and  bearded  barley  may  give  a cross- 
bred which  is  hooded,  whilst  by  using  another  bearded  barley 
a cross-bred  with  hoods  borne  on  awns  may  result.  One 
example  of  interest  from  several  points  of  view  is  afforded 
by  a cross  between  Rivet  wheat  and  Polish  (macaroni)  wheat. 
The  latter  has  very  long  glumes  (chaff).  The  glumes  of  the 
cross-bred  are  intermediate  in  size  between  the  two  parents,  so 
that  neither  the  large  type  of  glume  or  the  small  can  possibly 
be  called  dominant  or  recessive.  Nevertheless  the  progeny 
consists  of  the  following  tj'pes : large,  intermediate,  and  small 
glumes  in  the  proportion  of  1 : 2 : 1.  Evidently,  therefore,  the 
cross-bred  produces  large  and  small  gametes  in  approximately 
equal  proi)ortions.  If  the  gametes  carrying  the  large  glume 
character  meet  we  obtain  the  large  glumed  type,  if  the  small 
the  small,  if  large  and  small  meet,  as  in  the  original  operation 
of  crossing,  the  intermediate  type  results. 
All  the  evidence  which  has  accumulated  then  goes  to  show 
that  the  characters  of  the  plant  or  animal  are  distributed  among 
the  sex-cells  according  to  a definite  system,  and  the  possible 
combinations  of  these  characters  can  be  foretold  with  consider- 
able accuracy.  To  the  breeder  the  value  of  this  knowledge 
can  hardly  be  estimated.  Once  he  knows  the  behaviour  of 
particular  characters  of  the  varieties  he  is  working  with,  he 
can  definitely  choose  the  parents  which  will  give  him  the 
coml)ination  he  desires,  and  obtain  it,  fixed,  in  the  first  or 
at  the  latest  in  the  second  generation  from  the  cross-bred. 
This  is  worth  comparing  with  one’s  expectations  in  the  dark 
pre-Mendelian  days.  Then  one  might  by  chance  find  the 
required  tyi)e  among  the  mixture  resulting  from  the  cross-breds ; 
more  often  it  was  a case  of  the  selection  we  hear  so  much  of — 
the  picking  out  of  such  a form  as  the  rough-chaffed  red  wheat 
which  in  the  following  generation  might  breed  true,  or  with 
far  greater  probability  (the  chances  can  be  easily  calculated) 
would  break  iqj  into  a number  of  forms  similar  to  those  from 
which  it  was  originally  chosen.  A further  selection  from  the 
mass  would  in  all  probability  give  the  same  result.  Small 
wonder  is  it  then  that  competent  breeders  have  given  up  as 
hopeless  i)roblems  the  solution  of  which  we  now  know  to  be 
simple. 
One  concrete  case  will  show  the  value  of  Mendel’s  discoveries 
in  this  direction.  In  1875  Rimpau  crossed  together  a lax  red- 
chaffed  wheat  with  a dense  white-chaffed  wheat.  The  four 
types  of  red  and  white  lax  or  dense  ears  were  not  fixed  until 
1886.  Now  three  seasons  would  be  ample.  So  far  though  we 
know  little  of  the  i)ossil)ilities  of  introducing  absolutely  fresh 
characters  into  our  crops  and  stock ; we  are  simply  in  a position 
