﻿■ 
  Rickett: 
  Sphaerocarpos 
  Doxnellii 
  353 
  

  

  This 
  history 
  bears 
  a 
  striking 
  resemblance 
  to 
  that 
  of 
  the 
  spore- 
  

   lings 
  described 
  in 
  a 
  previous 
  paper 
  (5), 
  which 
  developed 
  from 
  spores 
  

   sown 
  in 
  a 
  nutrient 
  solution. 
  These 
  sporelings 
  were 
  marked 
  by 
  

   the 
  production 
  of 
  an 
  excessively 
  long 
  germ-tube, 
  which, 
  when 
  

   conditions 
  were 
  favorable, 
  gradually 
  broadened 
  out 
  into 
  the 
  

  

  thallus-plate. 
  

  

  / 
  

  

  were 
  formed 
  which 
  were 
  almost 
  identical 
  in 
  appearance 
  with 
  those 
  

   just 
  described 
  as 
  arising 
  by 
  regeneration. 
  Obviously 
  the 
  unusual 
  

   form 
  in 
  each 
  case 
  bears 
  much 
  the 
  same 
  relation 
  to 
  the 
  normal 
  or 
  

   common 
  method 
  of 
  development. 
  All 
  gradations 
  are 
  found 
  

   between 
  the 
  two 
  methods 
  among 
  both 
  sporelings 
  and 
  adventitious 
  

   shoots, 
  the 
  latter, 
  however, 
  being, 
  so 
  far 
  as 
  my 
  observations 
  have 
  

   shown, 
  by 
  far 
  the 
  more 
  variable. 
  

  

  In 
  cases 
  in 
  which 
  several 
  adjoining 
  cells 
  start 
  regeneration, 
  it 
  

   seems 
  that 
  the 
  growths 
  produced 
  by 
  each 
  may 
  become 
  fused 
  

   together 
  into 
  one 
  new 
  plant. 
  This 
  is 
  rather 
  difficult 
  to 
  determine, 
  

   but 
  it 
  is 
  certain 
  that 
  one 
  often 
  sees 
  many 
  contiguous 
  cells 
  starting 
  

   to 
  divide, 
  while 
  there 
  are 
  rarely 
  as 
  many 
  plants 
  formed 
  on 
  a 
  

   single 
  portion 
  of 
  tissue 
  as 
  would 
  represent 
  the 
  development 
  of 
  all 
  

   these 
  cells 
  into 
  separate 
  plants. 
  The 
  possibilities 
  suggested 
  are 
  

   that 
  fusion 
  may 
  occur, 
  two 
  or 
  more 
  cell 
  masses 
  growing 
  together 
  

   into 
  one 
  structure, 
  or 
  that 
  the 
  development 
  of 
  some 
  of 
  these 
  cell 
  

   masses 
  may 
  be 
  checked. 
  Fig. 
  14 
  shows 
  adventitious 
  growths 
  

   resulting 
  from 
  the 
  division 
  of 
  groups 
  of 
  adjacent 
  cells. 
  In 
  Figs. 
  

   15, 
  16, 
  and 
  19, 
  the 
  young 
  plants 
  seem 
  to 
  have 
  developed 
  each 
  

   from 
  a 
  single 
  marginal 
  cell 
  of 
  a 
  lobe, 
  the 
  base 
  of 
  the 
  shoot 
  not 
  

   being 
  much 
  wider 
  than 
  a 
  single 
  marginal 
  cell. 
  Fig. 
  18 
  represents 
  

   several 
  plants 
  arising 
  by 
  regeneration 
  from 
  the 
  margin 
  of 
  the 
  

   opening 
  of 
  an 
  involucre. 
  Here 
  also 
  each 
  plant 
  

   developed 
  from 
  a 
  single 
  cell. 
  Figs. 
  5 
  and 
  6 
  show 
  similar 
  groups 
  

   of 
  marginal 
  cells 
  at 
  an 
  earlier 
  stage 
  in 
  regeneration. 
  The 
  cell 
  

   masses 
  resulting 
  from 
  the 
  division 
  of 
  individual 
  marginal 
  cells 
  

   can 
  be 
  fairly 
  readily 
  distinguished, 
  and 
  seern 
  to 
  be 
  each 
  in 
  process 
  

   of 
  forming 
  independent 
  shoots; 
  but 
  there 
  are 
  other 
  cells 
  (x) 
  

   adjoining 
  these 
  which 
  have 
  also 
  divided, 
  and 
  it 
  is 
  impossible 
  to 
  

   say 
  whether 
  the 
  cell 
  groups 
  thus 
  formed 
  will 
  also 
  give 
  rise 
  each 
  to 
  

   a 
  separate 
  plant 
  or 
  whether 
  they 
  will 
  merely 
  contribute 
  to 
  the 
  

   cell 
  masses 
  formed 
  from 
  the 
  marginal 
  cells. 
  

  

  seems 
  

  

  