﻿10 
  Mr. 
  R. 
  Beer 
  and 
  Dr. 
  A. 
  Arber. 
  On 
  the 
  

  

  and 
  vessel 
  rudiments 
  of 
  the 
  root 
  of 
  several 
  species 
  of 
  Euphorbia 
  and 
  Ricinus, 
  

   but 
  these 
  plants 
  were 
  regarded 
  as 
  exceptions 
  to 
  the 
  general 
  rule 
  according 
  to 
  

   which 
  multinucleate 
  cells 
  arise 
  by 
  amitotic 
  divisions 
  of 
  the 
  cell 
  nucleus. 
  

  

  We 
  have 
  gone 
  very 
  carefully 
  into 
  the 
  question 
  of 
  the 
  origin 
  of 
  the 
  plurality 
  

   of 
  nuclei 
  in 
  the 
  multinucleate 
  cells 
  and 
  in 
  more 
  than 
  100 
  species 
  we 
  have 
  

   been 
  able 
  to 
  satisfy 
  ourselves 
  beyond 
  doubt 
  that 
  the 
  several 
  nuclei 
  have 
  

   arisen 
  by 
  mitotic 
  division. 
  No 
  single 
  instance 
  of 
  direct 
  nuclear 
  division 
  has 
  

   ever 
  been 
  observed 
  by 
  us 
  in 
  these 
  young 
  active 
  tissues. 
  

  

  The 
  Formation 
  of 
  Phragmospheres. 
  

  

  Certain 
  peculiarities 
  are 
  found 
  in 
  the 
  course 
  of 
  these 
  mitotic 
  divisions 
  which 
  

   appear 
  to 
  be 
  characteristic 
  of 
  multinucleate 
  cells. 
  We 
  briefly 
  referred 
  to 
  

   these 
  peculiarities 
  in 
  our 
  preliminary 
  note, 
  when 
  we 
  described 
  them 
  as 
  

   giving 
  rise 
  to 
  an 
  appearance 
  of 
  a 
  cell 
  lying 
  within 
  another 
  cell. 
  We 
  have 
  

   now 
  observed 
  this 
  modified 
  form 
  of 
  mitosis 
  in 
  the 
  young 
  vegetative 
  tissues 
  of 
  

   some 
  120 
  species 
  belonging 
  to 
  more 
  than 
  50 
  families, 
  including 
  representatives 
  

   of 
  Vascular 
  Cryptogams, 
  Gymnosperms, 
  and 
  Angiosperms. 
  We 
  therefore 
  

   feel 
  that 
  we 
  are 
  justified 
  in 
  regarding 
  the 
  process 
  observed 
  as 
  being 
  possibly 
  

   almost 
  universal 
  in 
  these 
  young 
  tissues. 
  

  

  In 
  cells 
  which 
  are 
  about 
  to 
  become 
  binucleate, 
  the 
  mitosis 
  proceeds 
  normally 
  

   up 
  to 
  the 
  spindle 
  stage 
  and 
  the 
  cell 
  plate 
  makes 
  its 
  appearance 
  as 
  usual 
  ; 
  it 
  

   does 
  not, 
  however, 
  give 
  rise 
  to 
  any 
  cell 
  membrane.- 
  It 
  is 
  apparently 
  resorbed, 
  

   and 
  the 
  whole 
  phragmoplast* 
  with 
  the 
  associated 
  cytoplasm 
  becomes 
  trans- 
  

   formed 
  into 
  a 
  hollow 
  sphere 
  which 
  encloses 
  the 
  daughter 
  nuclei 
  ; 
  this 
  sphere 
  

   gradually 
  increases 
  in 
  diameter, 
  ultimately 
  becoming 
  co-extensive 
  with 
  the 
  

   cytoplasm 
  lining 
  the 
  cell 
  wall. 
  For 
  this 
  hollow 
  shell, 
  which 
  represents 
  the 
  

   later 
  development 
  of 
  the 
  phragmoplast, 
  and 
  which, 
  in 
  the 
  case 
  of 
  binucleate 
  

   cells, 
  replaces 
  the 
  normal 
  apparatus 
  of 
  wall 
  formation, 
  we 
  propose 
  the 
  term 
  

   " 
  phragmosphere."f 
  The 
  spherical 
  shape 
  is 
  not 
  fully 
  exhibited 
  unless 
  the 
  

   karyokinetic 
  figure 
  occurs 
  in 
  the 
  centre 
  of 
  the 
  cell. 
  If, 
  as 
  often 
  happens, 
  it 
  

   occupies 
  a 
  position 
  close 
  to 
  a 
  wall, 
  the 
  sphere 
  at 
  an 
  early 
  stage 
  of 
  its 
  expansion 
  

   fuses 
  on 
  one 
  side 
  with 
  the 
  primordial 
  utricle 
  and 
  thus 
  loses 
  its 
  symmetry. 
  

   As 
  the 
  phragmosphere 
  extends, 
  the 
  paired 
  nuclei 
  gradually 
  move 
  apart 
  from 
  

   one 
  another, 
  while 
  they 
  develop 
  in 
  normal 
  fashion 
  and 
  ultimately 
  assume 
  the 
  

   ordinary 
  characters 
  of 
  resting 
  nuclei. 
  

  

  The 
  young 
  inflorescence 
  axis 
  of 
  Anthriscus 
  sylvestris 
  has 
  furnished 
  some 
  of 
  

  

  * 
  See 
  Errera, 
  L., 
  " 
  Ueber 
  Zellformen 
  und 
  Seifenblasen 
  : 
  ' 
  (Versaniml. 
  Deutsch. 
  Naturfor. 
  

   u. 
  Aerzte 
  in 
  Wiesbaden), 
  ' 
  Bot. 
  Centralbl.,' 
  vol. 
  34, 
  pp. 
  395-398 
  (1888). 
  

   t 
  *pay/idy 
  = 
  hedge, 
  fence, 
  etc. 
  ; 
  crcpmpa 
  = 
  sphere. 
  

  

  