﻿Brown: 
  

  

  REFRACTION 
  

  

  259 
  

  

  dilute 
  solution 
  of 
  xylol 
  dammar 
  (mounting 
  consistency 
  diluted 
  

   about 
  twenty 
  times) 
  on 
  the 
  transverse 
  face 
  of 
  the 
  dry 
  woody 
  

   tissue 
  to 
  be 
  tested. 
  Section 
  immediately 
  to 
  lO/x 
  and 
  mount 
  in 
  

   glycerine. 
  The 
  perforations 
  (Fig. 
  4) 
  each 
  with 
  a 
  small 
  globule 
  of 
  

   dammar 
  in 
  or 
  attached 
  to 
  It, 
  are 
  then 
  easily 
  visible 
  in 
  the 
  glycerine 
  

   medium. 
  The 
  cover 
  glass 
  may 
  be 
  cemented 
  with 
  gold 
  size, 
  after 
  

   the 
  manner 
  of 
  glycerine 
  permanent 
  mounts, 
  and 
  the 
  preparation 
  

   will 
  keep 
  for 
  at 
  least 
  several 
  weeks, 
  often 
  Improving 
  on 
  standing 
  a 
  

   few 
  days; 
  but 
  the 
  slide 
  should 
  always 
  be 
  kept 
  face 
  upward. 
  

  

  In 
  mounting 
  tissues 
  In 
  highly 
  refractive 
  media, 
  care 
  should 
  

   be 
  taken 
  to 
  press 
  the 
  cover 
  slip 
  \ 
  

  

  ^ 
  

  

  down 
  tightly 
  against 
  the 
  tissue, 
  

   to 
  exclude 
  any 
  excess 
  liquid 
  

   from 
  above 
  the 
  section. 
  With 
  

  

  quinidine, 
  for 
  example, 
  an 
  ef- 
  

   fect 
  of 
  chromatic 
  aberration 
  

   may 
  be 
  produced 
  by 
  a 
  film 
  of 
  

   the 
  liquid 
  between 
  the 
  lignified 
  

   membranes 
  of 
  the 
  section 
  and 
  

   the 
  cover 
  slip. 
  

  

  o 
  

  

  4 
  X 
  

  

  /-h.QOS 
  

  

  P 
  

  

  o 
  

  

  G 
  

  

  V. 
  SUMMARY 
  

  

  I. 
  In 
  the 
  fully 
  developed 
  

   tissues 
  examined, 
  the 
  refrac- 
  

   tive 
  Index 
  of 
  the 
  material 
  of 
  

  

  01 
  2 
  3 
  4- 
  5 
  L 
  

  

  to 
  fJ- 
  

  

  Fig. 
  4- 
  Bordered 
  pit 
  of 
  sugar 
  pine, 
  

   Pintis 
  Lamber 
  liana, 
  after 
  treatment 
  with 
  

   dammar 
  to 
  bring 
  out 
  perforations; 
  Z). 
  a 
  

  

  which 
  any 
  given 
  cell-membrane 
  large 
  globule 
  of 
  dammar 
  floating 
  partially 
  

  

  or 
  cell-content 
  Is 
  composed 
  is 
  ^^ee 
  in 
  the 
  glycerine 
  within 
  the 
  border 
  

   r 
  . 
  I 
  , 
  , 
  .1 
  -r 
  (5); 
  P, 
  perforations 
  through 
  the 
  closing 
  

  

  fairly 
  constant 
  with 
  uniiorm 
  \ 
  ,. 
  ., 
  . 
  , 
  

  

  ■^ 
  membrane, 
  arranged 
  in 
  a 
  circle 
  at 
  the 
  edge 
  

  

  conditions 
  of 
  temperature; 
  but 
  of 
  the 
  torus 
  and 
  visible 
  through 
  the 
  trans- 
  

  

  during 
  the 
  growth 
  of 
  a 
  tissue 
  parent 
  border; 
  G. 
  globules 
  of 
  dammar 
  de- 
  

  

  the 
  refraction 
  of 
  its 
  constituent 
  '^'^'^^^ 
  ^^°'" 
  perforation 
  at 
  edge 
  of 
  torus 
  

  

  and 
  floating 
  free 
  in 
  the 
  glycerine; 
  0, 
  

  

  materials 
  may 
  change 
  enorm- 
  orifice, 
  

   ously. 
  Such 
  changes 
  in 
  refrac- 
  

   tion 
  are 
  evidently 
  associated 
  with 
  corresponding 
  changes 
  in 
  the 
  

   chemical 
  composition. 
  

  

  2. 
  The 
  indices 
  of 
  refraction 
  of 
  the 
  various 
  membranes 
  and 
  

   other 
  elements, 
  of 
  which 
  mature 
  plant 
  tissues 
  are 
  composed, 
  

   differ 
  greatly 
  from 
  one 
  another, 
  and 
  a 
  given 
  tissue 
  complex 
  will 
  

  

  