﻿250 
  Browx: 
  The 
  refraction 
  of 
  light 
  in 
  plant 
  tissues 
  

  

  seen 
  

  

  given 
  membrane 
  may 
  deviate 
  widely 
  from 
  the 
  average 
  or 
  may 
  

   actually 
  change 
  during 
  growth. 
  

  

  I. 
  Relative 
  refraction 
  

  

  As 
  shown 
  in 
  Table 
  I, 
  there 
  is 
  no 
  single 
  index 
  of 
  refraction 
  which 
  

   is 
  common 
  to 
  even 
  the 
  different 
  membranes 
  of 
  a 
  tissue. 
  A 
  fair 
  

   average 
  for 
  dehydrated 
  tissues 
  would 
  be 
  1.53, 
  or 
  .01 
  above 
  that 
  

   of 
  Canada 
  balsam 
  or 
  dammar 
  (1.52); 
  but 
  the 
  refraction 
  of 
  many 
  

   bodies, 
  particularly 
  the 
  cell 
  contents, 
  differs 
  widely 
  from 
  the 
  mean. 
  

   For 
  the 
  dehydrated 
  tissues 
  examined 
  by 
  the 
  writer, 
  n 
  (the 
  index 
  

   of 
  refraction) 
  varies 
  from 
  1.50 
  to 
  1.59; 
  but 
  had 
  protoplasm 
  and 
  

   other 
  living 
  bodies 
  with 
  high 
  water 
  content 
  been 
  included, 
  far 
  

   lower 
  refractions 
  would 
  doubtless 
  have 
  been 
  found, 
  and 
  the 
  range 
  in 
  

   refraction 
  would 
  probably 
  have 
  been 
  about 
  three 
  times 
  as 
  great. 
  ' 
  

  

  2. 
  Deviation 
  in 
  refraction 
  with 
  imbibition 
  

  

  Certain 
  crystalline 
  bodies 
  found 
  in 
  plant 
  tissues, 
  such 
  as 
  the 
  

   crystals 
  of 
  calcium 
  oxalate, 
  do 
  not 
  become 
  invisible 
  in 
  any 
  of 
  the 
  

   refractive 
  liquids: 
  no 
  physical 
  change 
  takes 
  place 
  when 
  they 
  are 
  

   brought 
  in 
  contact 
  with 
  the 
  oil 
  mixtures 
  and 
  no 
  deviation 
  or 
  

   change 
  in 
  refraction 
  occurs. 
  An 
  organic 
  membrane 
  on 
  the 
  other 
  

   hand, 
  as 
  already 
  noted, 
  imbibes 
  the 
  liquid 
  in 
  which 
  it 
  is 
  mounted. 
  

   As 
  a 
  result 
  of 
  the 
  physical 
  change 
  which 
  thus 
  results 
  in 
  the 
  

   mass 
  of 
  the 
  membrane, 
  the 
  latter 
  becomes 
  invisible, 
  or 
  nearly 
  

   so, 
  in 
  two 
  or 
  more 
  consecutive 
  liquids 
  of 
  the 
  refractive 
  series, 
  

   namely, 
  in 
  those 
  whose 
  index 
  of 
  refraction 
  approaches 
  most 
  

   closely 
  that 
  of 
  the 
  membrane 
  after 
  it 
  has 
  absorbed 
  as 
  much 
  as 
  it 
  

   will 
  of 
  the 
  refractive 
  liquid 
  in 
  which 
  it 
  is 
  mounted. 
  In 
  other 
  

   words, 
  the 
  refraction 
  of 
  the 
  membrane 
  mass, 
  after 
  imbibition, 
  

   deviates 
  from 
  that 
  of 
  the 
  tissue 
  substance 
  according 
  to 
  the 
  volume 
  

   and 
  refractive 
  index 
  of 
  liquid 
  taken 
  up. 
  the 
  principle 
  involved 
  

   bemg 
  nearly 
  the 
  same 
  as 
  that 
  observed 
  in 
  preparing 
  the 
  series 
  

   of 
  refractive 
  liquids. 
  

  

  great 
  

  

  deviation 
  of 
  refraction. 
  Cuticle, 
  cork, 
  true 
  wood 
  fibers, 
  and 
  middle 
  

   lamella, 
  for 
  example, 
  show 
  relatively 
  little 
  deviation; 
  collenchyma 
  

   primary 
  cortex, 
  and 
  mucilaginous 
  membranes, 
  on 
  the 
  other 
  hand' 
  

  

  