﻿352 
  Rickett: 
  Sphaerocarpos 
  Doxxellii 
  

  

  After 
  the 
  young 
  plant 
  has 
  thus 
  become 
  a 
  distinct 
  outgrowth 
  

   from 
  the 
  parent 
  tissue, 
  cell 
  divisions 
  occur 
  in 
  many 
  planes, 
  so 
  

   that 
  there 
  is 
  formed 
  a 
  compact 
  mass 
  of 
  cells 
  several 
  cells 
  thick 
  in 
  

   each 
  dimension. 
  The 
  form 
  of 
  this 
  mass 
  is 
  globular 
  or 
  cylindrical, 
  

   and 
  there 
  is 
  no 
  longer 
  any 
  evidence 
  of 
  the 
  existence 
  of 
  an 
  apical 
  

  

  cell 
  (Figs. 
  5, 
  6). 
  

  

  The 
  only 
  exceptions 
  found 
  to 
  this 
  history 
  were 
  in 
  the 
  first 
  

   cases 
  of 
  regeneration 
  noted, 
  mentioned 
  above, 
  in 
  which 
  each 
  

   young 
  plant 
  grew 
  out 
  as 
  a 
  long 
  ribbon. 
  Presumably 
  this 
  took 
  

   place 
  by 
  the 
  continuation, 
  after 
  the 
  cell 
  mass 
  had 
  once 
  bulged 
  

   out 
  from 
  the 
  original 
  containing 
  wall, 
  of 
  divisions 
  similar 
  to 
  those 
  

   which 
  had 
  cut 
  up 
  the 
  original 
  mother 
  cell. 
  The 
  cell 
  at 
  the 
  tip 
  of 
  

  

  Figs. 
  7-12. 
  The 
  tips 
  of 
  filamentous 
  adventitious 
  shoots. 
  Figs. 
  8-10. 
  Develop- 
  

   ment 
  by 
  means 
  of 
  a 
  two-sided 
  apical 
  cell. 
  Figs, 
  ii, 
  12. 
  Broadening 
  of 
  the 
  apical 
  

   region 
  into 
  the 
  thallus-plate. 
  All, 
  X 
  150. 
  

  

  ; 
  

  

  such 
  a 
  ribbon-shaped 
  growth 
  had 
  in 
  most 
  cases 
  exactly 
  the 
  appear- 
  

   ance 
  of 
  a 
  two-sided 
  apical 
  cell, 
  cutting 
  off 
  segments 
  alternately 
  

   to 
  right 
  and 
  to 
  left. 
  The 
  segments 
  themselves 
  redivided 
  only 
  

   occasionally, 
  so 
  that 
  a 
  narrow 
  shoot, 
  two 
  cells 
  wide 
  and 
  one 
  cell 
  

   thick, 
  resulted. 
  The 
  tips 
  of 
  such 
  shoots 
  are 
  illustrated 
  in 
  Figs. 
  

   7, 
  8, 
  9, 
  10. 
  These 
  young 
  plants 
  finally 
  broadened 
  out 
  at 
  the 
  tip 
  

   (possibly 
  in 
  response 
  to 
  more 
  favorable 
  light 
  conditions), 
  and 
  the 
  

   ordinary 
  flat 
  plate-shaped 
  thallus 
  resulted. 
  As 
  soon 
  as 
  the 
  broad- 
  

   ening 
  had 
  occurred, 
  an 
  apical 
  cell 
  could 
  no 
  longer 
  be 
  distinguished, 
  

   further 
  growth 
  being 
  due 
  to 
  a 
  group 
  of 
  small 
  meristematic 
  cells 
  on 
  

   the 
  margm 
  of 
  the 
  plate, 
  either 
  in 
  an 
  apical 
  or 
  in 
  a 
  lateral 
  position 
  

  

  (Figs, 
  ii, 
  12, 
  19). 
  

  

  