﻿I 
  

  

  Brown: 
  The 
  refraction 
  of 
  light 
  in 
  plant 
  tissues 
  257 
  

  

  Tola. 
  — 
  This 
  oleo-resin 
  (balsam), 
  obtained 
  from 
  the 
  bark 
  of 
  a 
  

  

  ' 
  F 
  

  

  leguminous 
  tree, 
  Myroxylon 
  tohtijera 
  H. 
  B. 
  K., 
  of 
  South 
  America, 
  

   brings 
  out 
  satisfactorily 
  the 
  pitting 
  and 
  other 
  details 
  of 
  unstained 
  

   macerated 
  preparations. 
  

  

  Naphthalene 
  a 
  monobromated. 
  — 
  If 
  sections 
  are 
  thin, 
  naphthalene 
  

   a 
  monobromated 
  defines 
  clearly 
  all 
  tissues 
  of 
  the 
  stem. 
  Where 
  

   dehydration 
  can 
  be 
  accomplished 
  without 
  too 
  great 
  shrinkage 
  of 
  

   the 
  tissue, 
  details 
  such 
  as 
  the 
  pits 
  in 
  hypodermal 
  collenchyma 
  

   appear 
  very 
  distinctly. 
  This 
  oil 
  is 
  also 
  one 
  of 
  the 
  best 
  for 
  use 
  in 
  

   measuring 
  refraction 
  of 
  tissues 
  by 
  the 
  microscopic 
  method. 
  

  

  Quinidine.— 
  This 
  is 
  perhaps 
  the 
  most 
  satisfactory 
  medium 
  of 
  

   all 
  for 
  the 
  definition 
  of 
  minu^te 
  details. 
  Also, 
  all 
  tissues 
  of 
  the 
  

   bark 
  appear 
  clear 
  and 
  well 
  defined 
  except 
  for 
  details 
  affected 
  by 
  

   shrinkage 
  or 
  high 
  temperature. 
  In 
  using 
  this 
  organic 
  substance, 
  

   it 
  is 
  liquified 
  on 
  the 
  slide 
  at 
  a 
  temperature 
  above 
  that 
  of 
  boiling 
  

   water. 
  Professor 
  Hastings 
  states 
  that 
  quinidine 
  crystallizes 
  or 
  

   spoils 
  with 
  time 
  and, 
  further, 
  that 
  highly 
  refractive. 
  media, 
  such 
  

   as 
  quinidine, 
  tolu, 
  and 
  styrax, 
  define 
  with 
  great 
  clearness 
  the 
  

   minute 
  details 
  of 
  diatom 
  cysts. 
  

  

  2. 
  Pits 
  and 
  middle 
  lamella 
  in 
  collenchyma 
  

  

  The 
  part 
  played 
  by 
  refraction 
  in 
  bringing 
  out 
  details 
  may 
  be 
  

  

  F 
  

  

  'demonstrated 
  by 
  comparing 
  cross-sections 
  of 
  the 
  collenchyma 
  of 
  

   some 
  woody 
  stem, 
  such 
  as 
  Pyrus 
  communis 
  L. 
  or 
  Anctiba 
  japonica 
  

   Thunbg., 
  mounted 
  in 
  Canada 
  balsam 
  with 
  sections 
  mounted 
  in 
  

   other 
  media. 
  In 
  balsam 
  mounts 
  the 
  prominent 
  system 
  of 
  pits 
  

   connecting 
  the 
  cells 
  is 
  usually 
  obscured 
  (Fig. 
  3, 
  A), 
  whether 
  

   stained 
  or 
  not, 
  and 
  it 
  is 
  worthy 
  of 
  note, 
  in 
  this 
  connection, 
  that 
  

   the 
  presence 
  of 
  such 
  pits 
  in 
  the 
  collenchyma 
  of 
  woody 
  stems, 
  

   though 
  a 
  characteristic 
  feature 
  of 
  this 
  tissue 
  in 
  nearly 
  all 
  dicoty- 
  

   ledonous 
  trees 
  and 
  in 
  many 
  other 
  woody 
  plants, 
  has 
  seldom 
  been 
  

  

  r 
  

  

  noted 
  in 
  anatomical 
  drawings 
  or 
  descriptions, 
  even 
  in 
  such 
  stan- 
  

   dard 
  texts 
  as 
  that 
  of 
  Moeller 
  ('82), 
  although 
  it 
  can 
  be 
  readily 
  seen 
  

   when 
  in 
  sections 
  which 
  have 
  been 
  mounted 
  in 
  suitable 
  media 
  (Fig. 
  

   3, 
  B). 
  Thus, 
  this 
  pittingsystembecomes 
  very 
  clear 
  in 
  naphthalene 
  

  

  I 
  

  

  a 
  monobromated, 
  invisible 
  or 
  nearly 
  so 
  in 
  potassium 
  iodide-mercury 
  

   biniodlde, 
  and 
  visible 
  again 
  in 
  glycerine 
  (FiG. 
  3 
  B) 
  or 
  water. 
  

   The 
  middle 
  lamella, 
  however, 
  is 
  not 
  clearly 
  defined 
  in 
  any 
  of 
  these 
  

  

  