In  many  of  the  lower  plants,  the  cells  and  organs  of  which
are  only  slightly  differentiated,  all,  or  at  any  rate  many,  of  the
cells  can  individually  give  rise  to  a  new  plant  under  certain  cir-
cumstances. In  such  cases  we  might  be  inclined  to  suppose  that
each  cell  contained  originally,  i.e.  at  the  time  of  its  phyletic
origin,  the  entire  mass  of  determinants  of  the  species,  or,  in  other
words,  contained  germ-plasm.  The  various  differentiations  of
the  cells  on  the  upper  and  lower  surfaces,  for  instance,  would
consequently  depend  on  the  different  determinants  becoming
active  in  response  to  different  external  stimuli:  some,  for  in-
stance, might  be  stimulated  by  a  bright  light,  and  others  by  a
dim  light.
This  explanation  would  hardly  suffice  in  the  case  of  the  higher
plants,  the  differentiation  of  which  is  far  too  complicated  to  be
due  to  the  effect  of  external  causes.  A  large  number  of  the
cells  must  nevertheless  contain  germ-plasm,  which,  however,  is
in  the  unalterable  (*  gebundenen ')  state,  —  that  is  to  say,  it  is
not  merely  inactive,  but  is  incapable  at  the  time  of  undergoing
disintegration.  This  stage  in  the  phylogeny  of  gemmation  may
be  derived  from  the  earliest  stage.  As  the  plant  underwent  an
increasing  differentiation,  cells  appeared  which  only  contained
special  determinants,  in  addition  to  those  with  germ-plasm
proper ;  and  this  may  have  led  to  the  condition  which  we  now
find  in  the  highest  plants,  and  which  is  distinguished  by  the
fact  that  many  cells  only  contain  specific  determinants,  while  a
large  number  of  others  possess  in  addition  germ-plasm  in  the
unalterable  condition,  which  only  becomes  active  under  certain
influences.  I  shall  have  occasion  to  return  to  this  subject
later  on.
