﻿428 
  Rusk: 
  Protoplasmic 
  streaming 
  

  

  magnification 
  used 
  this 
  was 
  a 
  distance 
  of 
  595 
  microns, 
  (For 
  one 
  

   concentration 
  a 
  distance 
  of 
  420 
  microns 
  was 
  used.) 
  From 
  fifteen 
  

   to 
  eighteen 
  cells 
  were 
  tested 
  for 
  each 
  concentration. 
  For 
  the 
  

   sake 
  of 
  comparison 
  the 
  averages 
  were 
  reduced 
  to 
  seconds 
  per 
  100 
  

   microns, 
  and 
  as 
  for 
  Elodea, 
  results 
  are 
  also 
  given 
  in 
  terms 
  of 
  per 
  

  

  cent 
  acceleration 
  of 
  the 
  normal. 
  

  

  Since 
  the 
  test 
  and 
  control 
  observations 
  were 
  made 
  on 
  the 
  same 
  

   cells 
  in 
  every 
  case, 
  no 
  base 
  normal 
  rate 
  was 
  calculated; 
  the 
  average 
  

   of 
  the 
  normal 
  timings 
  of 
  the 
  particular 
  cells 
  tested 
  for 
  each 
  con- 
  

   centration, 
  was 
  used 
  as 
  the 
  normal 
  for 
  that 
  concentration. 
  

  

  The 
  work 
  with 
  Chara 
  was 
  more 
  satisfactory 
  than 
  that 
  with 
  

   Elodea 
  in 
  several 
  ways. 
  Because 
  of 
  the 
  larger 
  size 
  of 
  the 
  cells, 
  it 
  

   was 
  possible 
  to 
  time 
  the 
  movement 
  through 
  a 
  much 
  greater 
  

   distance, 
  thus 
  lessening 
  the 
  magnitnde 
  of 
  error. 
  It 
  was 
  

   possible 
  to 
  obtain 
  the 
  normal 
  rate 
  for 
  the 
  same 
  cells 
  that 
  were 
  

   tested, 
  thus 
  limiting 
  the 
  factor 
  of 
  individual 
  variation. 
  Because 
  

   of 
  the 
  greater 
  ease 
  of 
  making 
  observations 
  and 
  of 
  finding 
  suitable 
  

   cells, 
  it 
  was 
  possible, 
  with 
  the 
  same 
  expenditure 
  of 
  time, 
  to 
  make 
  

   tw^lce 
  as 
  many 
  observations 
  on 
  each 
  cell, 
  thus 
  again 
  lessening 
  

   the 
  magnitude 
  of 
  error. 
  

  

  To 
  prevent 
  the 
  crushing 
  of 
  Chara 
  cells, 
  the 
  cover-glass 
  was 
  

   supported 
  on 
  two 
  narrow 
  strips 
  of 
  glass, 
  cut 
  from 
  an 
  ordinary 
  

   slide. 
  In 
  general, 
  in 
  all 
  this 
  work, 
  observations 
  were 
  made 
  imme- 
  

   diately 
  upon 
  placing 
  the 
  material 
  under 
  the 
  microscope, 
  and 
  imme- 
  

   diately 
  after 
  placing 
  the 
  material 
  in 
  test 
  solutions. 
  However, 
  in 
  

   case 
  a 
  cell 
  showed 
  a 
  steady 
  rise 
  or 
  fall 
  in 
  its 
  rate, 
  observations 
  

   were 
  continued 
  until 
  the 
  rate 
  became 
  fairly 
  uniform 
  for 
  the 
  five 
  

   or 
  ten 
  necessary 
  consecutive 
  observations. 
  Uniformity 
  was 
  

   usually 
  reached 
  in 
  a 
  few 
  minutes. 
  

  

  By 
  reference 
  to 
  Table 
  I 
  and 
  Fig. 
  i, 
  it 
  will 
  be 
  seen 
  that 
  very 
  

   weak 
  zinc 
  sulphate 
  solutions, 
  0.0002 
  N 
  to 
  o.ooi 
  iV, 
  do 
  accelerate 
  

   the 
  movement 
  in 
  Elodea 
  cells. 
  The 
  concentration 
  at 
  which 
  the 
  

   greatest 
  acceleration 
  was 
  observed 
  was 
  0.0003 
  Ny 
  the 
  acceleration 
  

   being 
  14.85 
  per 
  cent 
  of 
  the 
  normal 
  rate. 
  Acceleration 
  becomes 
  

   less 
  blow 
  this 
  concentration, 
  and 
  also 
  falls 
  off 
  as 
  the 
  concentration 
  

   rises. 
  At 
  0.0015 
  ^ 
  retardation 
  is 
  seen. 
  There 
  appears 
  to 
  be 
  some 
  

   irregularity 
  in 
  the 
  retardation, 
  but 
  that 
  was 
  not 
  the 
  phenomenon 
  

   of 
  special 
  interest 
  in 
  this 
  study. 
  By 
  reference 
  to 
  Table 
  II 
  and 
  

  

  