﻿Brown: 
  The 
  refraction 
  of 
  light 
  in 
  plant 
  tissues 
  255 
  

  

  TABLE 
  II 
  

  

  Refraction 
  of 
  media 
  

  

  Index 
  of 
  refrattion 
  

  

  1. 
  Water. 
  133^ 
  

  

  2. 
  Alcohol 
  1.37 
  

  

  3. 
  Fluorite 
  1.433 
  

  

  4. 
  Glycerine 
  jelly 
  " 
  1.44 
  

  

  5. 
  Glycerine 
  .' 
  1.46-1.47 
  

  

  6. 
  Castor 
  oil 
  1.49 
  

  

  7. 
  Xylol 
  '. 
  . 
  . 
  . 
  1.50 
  

  

  8. 
  Oil 
  of 
  red 
  cedar 
  {Jiiniperus 
  procera) 
  ' 
  1.512 
  

  

  9. 
  Crown 
  glass 
  i-5i8 
  

  

  JO. 
  Dammar; 
  Canada 
  balsam 
  ; 
  1.52 
  

  

  11. 
  Clove 
  oil 
  1.535 
  

  

  12. 
  Quartz 
  ^-544 
  

  

  13. 
  Stj-rax 
  1.58 
  

  

  14. 
  McLean's 
  solution; 
  flint 
  glass 
  - 
  1.621 
  

  

  15. 
  Balsam 
  of 
  Tolu 
  T 
  1.628 
  

  

  16. 
  Naphthalene 
  a 
  monobromated 
  1.65 
  

  

  w 
  

  

  17. 
  Iceland 
  spar 
  (calcium 
  carbonate) 
  (Hastings 
  '88) 
  . 
  .,...1.658 
  and 
  1.48 
  

  

  w 
  

  

  18. 
  Tolu 
  dissolved 
  in 
  naphthalene 
  a 
  monobromated 
  " 
  1.72 
  

  

  19. 
  Quinidine 
  i.S? 
  

  

  A 
  few 
  comments 
  on 
  some 
  of 
  the 
  various 
  media 
  listed 
  may 
  be 
  

   made: 
  

  

  Water; 
  alcohol. 
  — 
  These 
  media 
  have 
  an 
  index 
  of 
  refraction 
  far 
  

   below 
  (a 
  difference 
  of 
  about 
  —0.20) 
  that 
  of 
  the 
  average 
  for 
  plant 
  

   tissues. 
  If 
  the 
  section 
  is 
  thin, 
  these 
  media 
  have 
  no 
  superior 
  for 
  

   the 
  definition 
  of 
  minute 
  details 
  in 
  tissues 
  which 
  shrink 
  on 
  dehy- 
  

   dration. 
  But, 
  on 
  the 
  other 
  hand, 
  a 
  section 
  of 
  ordinary 
  thickness 
  

   (20-70 
  p) 
  lacks 
  transparency 
  in 
  these 
  mefiia 
  and 
  the 
  outlines 
  

   are 
  confused. 
  In 
  such 
  sections, 
  greater 
  transparency 
  and 
  there- 
  

   fore 
  clearer 
  definition 
  may 
  be 
  obtained 
  by 
  mounting 
  in 
  some 
  

   medium 
  such 
  as 
  xylol, 
  whose 
  index 
  of 
  refraction 
  differs 
  but 
  little 
  

  

  (about 
  0.02) 
  from 
  that 
  of 
  the 
  tissue. 
  , 
  * 
  

  

  Glycerine; 
  glycerine 
  jelly.— 
  Vnstalncd 
  sections 
  of 
  stem 
  tissues, 
  

  

  from 
  which 
  air 
  has 
  been 
  removed 
  by 
  standing 
  in 
  alcohol, 
  mounted 
  

   in 
  glycerine 
  and 
  permanently 
  cemented 
  with 
  Brunswick 
  black 
  or 
  

   gold 
  size, 
  require 
  little 
  time 
  to 
  prepare 
  and 
  are 
  frequently 
  superior 
  

   to 
  stained 
  sections 
  for 
  observing 
  minute 
  details 
  such 
  as 
  the 
  pitting 
  

   of 
  fibers 
  or 
  vessels^ 
  as 
  well 
  as 
  the 
  broader 
  details 
  of 
  outline. 
  Gly- 
  

   cerine 
  jelly 
  is 
  particularly 
  to 
  be 
  recommended 
  for 
  unstained 
  

   sections 
  of 
  woody 
  tissues. 
  

  

  