342 
MendeVi^  Lair.s  of  Hereditjf. 
The  following  generation  showed  that  these  extracted  re- 
cessives  and  dominants  again  bred  true  whilst  the  cross-bred 
forms  broke  up  as  before.  In  more  complex  cases,  such  as 
crosses  between  races  differing  in  more  than  one  pair  of 
characters,  Mendel’s  Laws  were  again  found  to  hold  with  the 
same  accuracy.  As  an  example  we  may  (]uote  the  case  of  a 
cross  between  Rough  Chaff  and  Golden  Drop,  i.e.,  a white, 
rough-chaffed  wheat  x a red  smooth-chaffed  wheat.  Here  the 
rough  chaff  (A)  and  the  red  colour  {B)  are  dominant,  the 
smooth  chaff  (a)  and  the  white  coloui'  {h)  recessive. 
The  cross-bred  was  rough-chaffed  and  red.  Its  progeny, 
after  self-fertilisation,  consisted  of  four  types  of  individuals  : — 
rough-chaffed  red  {AB),  rough-chaffed  white  (A^»),  smooth- 
chaffed  red  {aB),  and  smooth-chaffed  white  (ah),  in  the  pro- 
portion of  9 : 3 : 3 : I.  In  this  generation,  therefore,  we  have 
two  new  types  appearing  AB  and  ah — as  well  as  the  parental 
forms  Ah  and  aB. 
After  self-fertilisation  the  individuals  of  this  generation 
behaved  as  follows  : — 
Rough-cliatFed  red. 
AB. 
Rough-chaffed  white. 
Sniooth-ctiaffed  red. 
/ AR  rough-chaffed  red,  AB. 
I Rough-chaffed  red  and  white,  .47?  and  Ah. 
Rough-cliaffed  red  and  smooth-ciiaffed  red,  AB 
■<  and  aB. 
Rough-chaffed  red,  rough-ciiaffed  wliite,  smooth- 
ctiafled  red,  smooth-chaffed  white,  -47^,  Ah, 
\ aB,  and  ah. 
j AU  rough-chaffed  wliite.  Ah. 
I Rough-  and  smooth-chaffed  white,  Ah  and  ah. 
I All  smooth-chaffed  red,  a B. 
\ Smooth-chaffed  red  and  white,  aB  and  ah. 
Smooth-chaffed  white.  All  smooth-chaffed  white,  ah. 
From  this  it  is  evident  that  the  rough-chaffed  red  indi- 
viduals were  gametically  either  AB,  ABh,  AaB,  or  AaBh  ; 
the  rough-chaffed  white  either  Ah  or  Aah  ; the  smooth-chaffed 
red  either  aB  or  ah  ; the  smooth-chaffed  white  all  ah. 
The  next  generation  from  the  plots  which  had  produced 
the  one  type  only,  that  is  where  the  individuals  composing 
them  were  all  rough-chaffed  and  red  (A/?),  or  all  smooth- 
chaffed  and  white  (ah),  &c.,  showed  that  these  types  were 
fixed,  for  they  bred  true  without  exception. 
As  the  result  of  this  cross  we  have  therefore  four  fixed 
types,  two  of  which — the  rough-chaffed  red  and  the  smooth- 
chaffed  white — are  new,  and  two — the  rough-chaffed  white  and 
the  smooth-chaffed  red — which  cannot  be  distinguished  from 
the  iiarental  forms.  By  in-breeding  from  cross-lireds  we  have 
therefore  reproduced  the  parent  types.  In  the  same  way  from 
other  crosses  where  Rivet  wheat  was  one  parent  a pure  Rivet 
