﻿260 
  Broayn: 
  The 
  refraction 
  of 
  light 
  in 
  plant 
  tissues 
  

  

  rarely 
  if 
  ever 
  have 
  a 
  single 
  refractive 
  index, 
  A 
  fair 
  average, 
  

   however, 
  would 
  be 
  about 
  1.53, 
  or 
  .01 
  above 
  that 
  of 
  Canada 
  balsam. 
  

  

  3. 
  Most 
  tissues 
  readily 
  absorb 
  water 
  and 
  other 
  refractive 
  

   liquids, 
  in 
  differing 
  amount 
  according 
  to 
  the 
  hygroscopic 
  qualities 
  

   of 
  the 
  tissue. 
  This 
  causes 
  the 
  refraction 
  of 
  the 
  mass 
  (tissue 
  

   substance 
  -f- 
  imbibition 
  liquid) 
  to 
  deviate 
  correspondingly 
  from 
  

   that 
  of 
  the 
  tissue 
  substance. 
  The 
  refractive 
  index 
  of 
  the 
  mem- 
  

   brane 
  mass 
  is 
  highly 
  sensitive 
  to 
  physical 
  changes 
  of 
  this 
  kind. 
  

  

  4. 
  The 
  laws 
  of 
  refraction 
  have 
  their 
  special 
  application 
  to 
  the 
  

   investigation 
  of 
  both 
  the 
  anatomical 
  characters 
  and 
  the 
  physical 
  

  

  * 
  and 
  chemical 
  properties 
  of 
  plant 
  tissues. 
  

  

  5. 
  With 
  average 
  sections, 
  clearer 
  definition 
  is 
  obtained 
  when 
  

   the 
  index 
  of 
  refraction 
  of 
  the 
  medium 
  is 
  below, 
  rather 
  than 
  above, 
  

   that 
  of 
  the 
  tissue 
  substance. 
  A 
  difference 
  of 
  at 
  least 
  ,05 
  between 
  

   tissue 
  mass 
  and 
  the 
  medium 
  in 
  which 
  it 
  is 
  mounted 
  is 
  desirable 
  to 
  

  

  m 
  

  

  obtain 
  clear 
  definition 
  of 
  small 
  perforations 
  and 
  similar 
  minute 
  

   details, 
  and 
  highly 
  refractive 
  media 
  such 
  as 
  styrax, 
  tolu, 
  and 
  

   quinidine 
  bring 
  out 
  such 
  details 
  with 
  the 
  greatest 
  possible 
  clear- 
  

   ness; 
  in 
  moderately 
  thin 
  sections, 
  a 
  difference 
  of 
  .005 
  is 
  sufficient 
  

   for 
  the 
  definition 
  of 
  general 
  outlines, 
  and 
  may 
  give 
  clearer 
  defini- 
  

   tion 
  for 
  general 
  features 
  than 
  a 
  greater 
  difference 
  in 
  refraction. 
  

  

  r 
  

  

  6. 
  In 
  selecting 
  a 
  medium, 
  to 
  obtain 
  a 
  given 
  difference 
  in 
  refrac- 
  

  

  ■ 
  

  

  tion 
  between 
  it 
  and 
  the 
  tissue 
  mass, 
  due 
  allowance 
  must 
  be 
  made 
  

   for 
  the 
  deviation 
  in 
  refraction 
  brought 
  about 
  by 
  the 
  imbibition 
  of 
  

   liquid 
  by 
  the 
  tissue. 
  

  

  Yale 
  University 
  

  

  Literature 
  cited 
  

  

  Brown, 
  F. 
  B. 
  H. 
  '19. 
  The 
  preparation 
  and 
  treatment 
  of 
  woods 
  for 
  

  

  microscopic 
  study.* 
  Bull. 
  Torrey 
  Club 
  46: 
  127-150./, 
  1-6. 
  

   Hastings, 
  C. 
  S. 
  '88. 
  On 
  the 
  law 
  of 
  double 
  refraction 
  in 
  Iceland 
  spar. 
  

  

  J 
  

  

  -y 
  

  

  McLean, 
  R. 
  C. 
  '14. 
  A 
  new 
  method 
  of 
  staining 
  Cyanophyceae. 
  

  

  New 
  Phytol. 
  13: 
  71-72. 
  

   Moeller, 
  J. 
  ^82. 
  Anatomie 
  der 
  Baumrinden. 
  Berlin. 
  

   Neefif, 
  F. 
  '14. 
  Uber 
  Zellumlagerung 
  — 
  Ein 
  Beitrag 
  zur 
  experimentellen 
  

  

  Anatomie. 
  

  

  / 
  

  

  Wright, 
  F, 
  E. 
  '11. 
  The 
  methods 
  of 
  petrographic-microscopic 
  

   research, 
  their 
  relative 
  accuracy 
  and 
  range 
  of 
  application, 
  Publ. 
  

   Carnegie 
  Inst. 
  Washington, 
  No, 
  158. 
  

  

  