﻿Rusk: 
  Protoplasmic 
  streaming 
  427 
  

  

  water 
  was 
  mounted 
  and 
  observed 
  similarly. 
  This 
  whole 
  proceed- 
  

   ing 
  was 
  carried 
  on 
  within 
  two 
  hours 
  and 
  a 
  half. 
  

  

  ■ 
  M 
  

  

  For 
  the 
  last 
  part 
  of 
  the 
  work 
  with 
  Elodea, 
  the 
  method 
  was 
  

   changed 
  in 
  the 
  following 
  way: 
  The 
  control 
  observ^ations 
  were 
  

   made 
  first. 
  Then 
  the 
  same 
  leaf 
  was 
  put 
  into 
  the 
  zinc 
  sulphate 
  

   solution 
  and 
  observed 
  again. 
  It 
  was 
  impossible, 
  however, 
  to 
  

   test 
  the 
  same 
  cells 
  again. 
  The 
  whole 
  observation 
  was 
  made 
  

   within 
  an 
  hour 
  and 
  a 
  half; 
  and 
  the 
  specimens 
  were 
  left 
  in 
  the 
  zinc 
  

  

  ^ 
  

  

  sulphate 
  solution 
  not 
  more 
  than 
  an 
  hour. 
  

  

  The 
  time 
  required 
  for 
  a 
  chloroplast 
  to 
  be 
  carried 
  the 
  length 
  of 
  

  

  L 
  

  

  the 
  cell 
  was 
  determined 
  with 
  a 
  stop-watch 
  that 
  could 
  be 
  read 
  to 
  

   tenths 
  of 
  a 
  second. 
  Five 
  such 
  observatons 
  were 
  made 
  for 
  each 
  

   cell 
  and 
  averaged. 
  The 
  length 
  of 
  the 
  cell 
  was 
  then 
  measured 
  with 
  

   a 
  micrometer 
  eyepiece. 
  From 
  twelve 
  to 
  twenty-five 
  cells 
  were 
  

   tested 
  for 
  each 
  concentration 
  used. 
  The 
  lengths 
  of 
  the 
  cells 
  

   timed 
  in 
  one 
  concentration 
  were 
  averaged; 
  the 
  average 
  timings 
  

   for 
  the 
  cells 
  timed 
  in 
  one 
  concentration 
  were 
  averaged; 
  and 
  the 
  

   results 
  were 
  reduced 
  so 
  as 
  to 
  express 
  the 
  rate 
  of 
  movement 
  for 
  

   the 
  concentration 
  in 
  terms 
  of 
  seconds 
  per 
  lOO 
  microns. 
  The 
  

   results 
  are 
  also 
  expressed 
  in 
  terms 
  of 
  per 
  cent 
  acceleration 
  or 
  retar- 
  

   dation 
  of 
  the 
  normal, 
  or 
  control, 
  rate. 
  

  

  Most 
  of 
  the 
  zinc 
  sulphate 
  test 
  observations 
  were 
  made 
  on 
  

   different 
  leaves 
  from 
  the 
  controls, 
  and 
  all 
  were 
  made 
  on 
  different 
  

   cells 
  from 
  the 
  controls. 
  On 
  this 
  account, 
  a 
  general 
  average 
  of 
  all 
  

   the 
  normal 
  observations 
  was 
  considered 
  the 
  best 
  control 
  to 
  use 
  for 
  

  

  m 
  

  

  all 
  concentrations. 
  This 
  base 
  normal 
  rate 
  was 
  an 
  average 
  of 
  the 
  

   timings 
  of 
  137 
  cells. 
  

  

  For 
  all 
  the 
  work 
  with 
  Chara 
  the 
  following 
  method 
  was 
  used; 
  

   A 
  healthy-looking 
  piece 
  was 
  taken 
  from 
  the 
  tip 
  of 
  a 
  plant, 
  and 
  

  

  observation 
  

  

  The 
  

  

  piece 
  was 
  then 
  put 
  into 
  the 
  test 
  solution, 
  and 
  new 
  observations 
  

   were 
  made 
  on 
  the 
  same 
  cells. 
  Ten 
  normal 
  and 
  ten 
  test 
  observa- 
  

   tions 
  were 
  made 
  for 
  each 
  cell. 
  All 
  the 
  observations 
  on 
  one 
  piece 
  

   w^ere 
  made 
  within 
  an 
  hour 
  and 
  a 
  half; 
  and, 
  for 
  the 
  most 
  part, 
  one 
  

   piece 
  was 
  left 
  in 
  the 
  test 
  solution 
  not 
  longer 
  than 
  three 
  quarters 
  

   of 
  an 
  hour. 
  

  

  The 
  time 
  required 
  for 
  a 
  particle 
  in 
  the 
  cytoplasm 
  to 
  be 
  carried 
  

   the 
  whole 
  length 
  of 
  the 
  micrometer 
  scale 
  was 
  determined 
  ; 
  under 
  the 
  

  

  