﻿iii 
  

  

  In 
  1832 
  he 
  also 
  described 
  the 
  movements 
  due 
  to 
  irritability 
  in 
  various 
  

   species 
  of 
  Robinia. 
  In 
  a 
  paper 
  on 
  Lenticels 
  he 
  disproved 
  the 
  theory 
  of 
  

   De 
  Candolle 
  that 
  these 
  structures 
  were 
  in 
  any 
  way 
  dependent 
  on 
  the 
  

   production 
  of 
  adventitious 
  roots. 
  His 
  memoir 
  on 
  the 
  stems 
  of 
  Cycads 
  

   appeared 
  also 
  this 
  year. 
  

  

  In 
  1833 
  he 
  worked 
  out 
  the 
  anomalous 
  structure 
  of 
  the 
  stomata 
  in 
  the 
  

   Proteaceae, 
  which 
  Robert 
  Brown 
  had 
  regarded 
  as 
  imperforate 
  and 
  had 
  

   described 
  simply 
  as 
  " 
  glandulse 
  cutaneae." 
  He 
  contributed 
  to 
  the 
  ' 
  Icones 
  

   Plantarum 
  Cryptogamicarum 
  Brasiliae 
  ' 
  of 
  Yon 
  Martius 
  a 
  description 
  of 
  

   the 
  anatomy 
  of 
  the 
  stem 
  of 
  tree 
  ferns. 
  Hitherto 
  the 
  course 
  of 
  their 
  

   vascular 
  bundles 
  had 
  been 
  supposed 
  to 
  be 
  very 
  similar 
  to 
  that 
  of 
  Mono- 
  

   cotyledons. 
  Yon 
  Mohl 
  was 
  the 
  first 
  to 
  explain 
  the 
  structure 
  of 
  the 
  hollow 
  

   fenestrated 
  cylinder 
  into 
  which 
  the 
  bundles 
  are 
  combined, 
  and 
  subsequent 
  

   observers 
  have 
  added 
  little 
  to 
  his 
  account. 
  In 
  a 
  memoir 
  published 
  in 
  

   the 
  ' 
  Flora 
  ' 
  he 
  described 
  the 
  development 
  of 
  the 
  spores 
  in 
  various 
  of 
  the 
  

   higher 
  Cryptogams. 
  He 
  gave 
  the 
  first 
  accurate 
  account 
  of 
  the 
  develop- 
  

   ment 
  of 
  the 
  moss-capsule, 
  pointed 
  out 
  the 
  development 
  of 
  the 
  spores 
  in 
  

   fours 
  in 
  one 
  mother-cell, 
  explained 
  the 
  development 
  of 
  the 
  elaters 
  of 
  

   Jungermannias, 
  and 
  gave 
  a 
  correct 
  account 
  of 
  those 
  of 
  Equisetum. 
  

  

  In 
  1834 
  he 
  published 
  an 
  elaborate 
  paper 
  on 
  pollen, 
  in 
  which 
  he 
  detailed 
  

   an 
  immense 
  number 
  of 
  observations. 
  It 
  is 
  true 
  he 
  fell 
  into 
  error 
  in 
  

   regarding 
  the 
  external 
  coat 
  as 
  in 
  some 
  cases 
  itself 
  cellular. 
  On 
  the 
  other 
  

   hand, 
  he 
  was 
  able 
  to 
  correct 
  Robert 
  Brown, 
  who, 
  in 
  describing 
  the 
  pecu- 
  

   liar 
  movements 
  (which 
  have 
  been 
  called 
  after 
  him) 
  in 
  the 
  granules 
  of 
  the 
  

   fovilla 
  of 
  pollen, 
  attributed 
  to 
  the 
  granules 
  at 
  the 
  same 
  time 
  a 
  change 
  of 
  

   form. 
  Yon 
  Mohl 
  also 
  established 
  the 
  development 
  of 
  the 
  pollen-grains 
  

   in 
  fours 
  within 
  each 
  mother-cell, 
  thus 
  indicating 
  an 
  analogy 
  with 
  the 
  

   development 
  of 
  spores 
  in 
  Cryptogams. 
  

  

  The 
  publication 
  by 
  Yon 
  Mohl 
  in 
  1835 
  of 
  his 
  discovery 
  of 
  the 
  multiplica- 
  

   tion 
  of 
  cells 
  by 
  division 
  (' 
  Ueber 
  die 
  Yermehrung 
  der 
  Pflanzenzellen 
  durch 
  

   Theilung') 
  in 
  Claclophora 
  glomerata 
  has 
  been 
  the 
  starting-point 
  of 
  all 
  

   subsequent 
  investigations 
  into 
  the 
  development 
  of 
  the 
  tissues 
  and 
  organs 
  

   of 
  plants. 
  It 
  revealed, 
  in 
  fact, 
  the 
  precise 
  mode 
  by 
  which 
  vegetative 
  

   growth 
  is 
  accomplished. 
  Mirbel, 
  in 
  his 
  memoir 
  on 
  the 
  development 
  of 
  

   Marchantia, 
  communicated 
  to 
  the 
  Academie 
  des 
  Sciences 
  in 
  1831 
  and 
  

   1832, 
  but 
  not 
  published 
  till 
  1836, 
  had 
  described 
  the 
  formation 
  of 
  pollen- 
  

   grains 
  by 
  the 
  quadripartite 
  division 
  of 
  a 
  mother-cell. 
  This, 
  however, 
  

   though 
  an 
  extremely 
  important 
  observation, 
  is 
  not 
  a 
  case 
  of 
  growth, 
  pro- 
  

   perly 
  speaking, 
  and 
  does 
  not 
  affect 
  Mohl's 
  historical 
  position 
  in 
  the 
  matter. 
  

   In 
  1838 
  Schleiden 
  announced 
  the 
  multiplication 
  of 
  cells 
  by 
  the 
  formation 
  

   of 
  new 
  cells 
  in 
  their 
  interior 
  as 
  a 
  general 
  law 
  in 
  the 
  vegetable 
  kingdom. 
  

   He 
  was 
  supported 
  by 
  Nageli. 
  The 
  views 
  of 
  Yon 
  Mohl, 
  developed 
  as 
  they 
  

   were 
  by 
  Meyen 
  and 
  Unger, 
  eventually 
  established 
  themselves. 
  In 
  a 
  

   paper 
  on 
  the 
  structure 
  of 
  cork 
  and 
  bark, 
  Yon 
  Mohl 
  described 
  the 
  nature 
  

   of 
  the 
  tissues 
  which 
  enter 
  into 
  their 
  composition, 
  and 
  accounted 
  for 
  the 
  

  

  a 
  2 
  

  

  