﻿Botany. 
  77 
  

  

  had 
  a 
  temperature 
  of 
  S00° 
  C, 
  the 
  difference 
  in 
  temperature 
  

   between 
  the 
  two 
  being 
  1000° 
  C. 
  . 
  . 
  . 
  

  

  It 
  is 
  probable 
  that 
  plant 
  structures 
  are 
  deficient 
  in 
  thermal 
  

   transparency, 
  and 
  they 
  are 
  notoriously 
  indifferent 
  conductors. 
  

   Nevertheless 
  it 
  is 
  difficult 
  to 
  believe 
  that 
  in 
  the 
  case 
  of 
  such 
  small 
  

   bodies 
  as 
  seeds, 
  their 
  being 
  brought 
  to 
  the 
  temperature 
  with 
  

   which 
  they 
  are 
  surrounded 
  can 
  be 
  more 
  than 
  a 
  question 
  of 
  time. 
  

  

  That 
  the 
  thermal 
  opacity 
  of 
  at 
  least 
  the 
  seed-coats, 
  may 
  be 
  

   really 
  considerable 
  is 
  not^ 
  however, 
  impossible, 
  even 
  at 
  low 
  tem- 
  

   peratures. 
  The 
  following 
  remarks 
  by 
  Professor 
  Dewar 
  have 
  an 
  

   obvious 
  bearing 
  on 
  this 
  point 
  : 
  — 
  

  

  1 
  Pictet, 
  after 
  an 
  elaborate 
  investigation, 
  concluded 
  that 
  below 
  

   a 
  certain 
  temperature 
  all 
  substances 
  had 
  practically 
  the 
  same 
  

   thermal 
  transparency, 
  and 
  that 
  a 
  non-conducting 
  body 
  became 
  

   ineffective 
  at 
  low 
  temperatures 
  iu 
  shielding 
  a 
  vessel 
  from 
  the 
  

   influx 
  of 
  heat. 
  Experiments, 
  however, 
  prove 
  that 
  such 
  is 
  not 
  the 
  

   ease, 
  the 
  transference 
  of 
  heat 
  observed 
  by 
  Pictet 
  appearing 
  to 
  be 
  

   due, 
  not 
  so 
  much 
  to 
  the 
  materials 
  themselves, 
  as 
  to 
  the 
  air 
  con- 
  

   tained 
  in 
  their 
  interstices. 
  Good 
  exhaustion 
  in 
  the 
  ordinary 
  

   vacuum 
  vessels 
  used 
  in 
  low 
  temperature 
  work, 
  reduces 
  the 
  influx 
  

   of 
  heat 
  to 
  one-filth 
  of 
  what 
  is 
  conveyed 
  when 
  the 
  annular 
  space 
  of 
  

   such 
  double-walled 
  vessels 
  is 
  filled 
  with 
  air.' 
  * 
  

  

  It 
  is 
  to 
  be 
  noticed 
  that 
  in 
  Professor 
  Dewar's 
  first 
  experiment 
  

   the 
  seeds 
  were 
  practically 
  in 
  a 
  vacuum. 
  It 
  is 
  obvious 
  from 
  what 
  

   has 
  been 
  quoted 
  above, 
  that 
  this 
  would 
  help 
  them 
  to 
  retain 
  their 
  

   heat. 
  Any 
  hesitation 
  in 
  accepting 
  the 
  results 
  of 
  the 
  experiment 
  

   on 
  this 
  ground 
  is, 
  however, 
  swept 
  away 
  by 
  the 
  second 
  experi- 
  

   ment, 
  in 
  which 
  the 
  seeds, 
  with 
  absolutely 
  no 
  protection 
  at 
  all, 
  were 
  

   actually 
  soaked 
  in 
  liquid 
  hydrogen 
  for 
  six 
  hours. 
  The 
  extremity 
  

   of 
  caution 
  can 
  hardly 
  resist 
  the 
  conclusion 
  that 
  they 
  must 
  have 
  

   been 
  brought 
  to 
  the 
  same 
  temperature. 
  

  

  Professor 
  Dewar 
  finds 
  ' 
  that 
  silica, 
  charcoal, 
  lampblack, 
  and 
  

   oxide 
  of 
  bismuth, 
  all 
  increase 
  the 
  insulation 
  to 
  four, 
  five 
  and 
  six 
  

   times 
  that 
  of 
  the 
  empty 
  vacuum 
  space.' 
  It 
  might 
  possibly 
  be 
  

   worth 
  while 
  to 
  try 
  how 
  far 
  a 
  packing 
  of 
  small 
  air-dry 
  seeds 
  

   would 
  compare, 
  say 
  with 
  charcoal. 
  And 
  this 
  would 
  in 
  some 
  

   degree 
  be 
  a 
  measure 
  of 
  the 
  thermal 
  transparency 
  of 
  seed 
  

   structures." 
  

  

  2. 
  Praxis 
  unci 
  Theorie 
  der 
  Zellen- 
  und 
  Befruchtungslehre 
  ; 
  von 
  

   Dr. 
  V. 
  Hacker 
  (Freiburg 
  i. 
  Br.) 
  Jena, 
  Gustav 
  Fischer, 
  1899. 
  

  

  Fixirung, 
  Fdrbung, 
  und 
  JBau 
  des 
  Protoplasmas 
  ,' 
  von 
  Dr. 
  A. 
  

   Fischer 
  (Leipzig), 
  Jena, 
  Gustav 
  Fischer 
  7 
  1899. 
  — 
  We 
  have 
  

   brought 
  these 
  two 
  books 
  together 
  under 
  observation 
  in 
  the 
  

   present 
  notice, 
  as 
  interesting 
  examples 
  of 
  the 
  exhaustive 
  charac- 
  

   ter 
  of 
  the 
  work 
  which 
  is 
  now 
  going 
  on 
  in 
  that 
  department 
  of 
  

   investigation 
  which 
  deals 
  with 
  the 
  cell. 
  These 
  studies 
  sweep 
  

   through 
  the 
  whole 
  range 
  from 
  the 
  suggestive 
  resemblances 
  to 
  

   organized 
  substances 
  which 
  are 
  found 
  in 
  or 
  can 
  be 
  produced 
  in 
  

  

  *'• 
  On 
  Liquid 
  Air 
  as 
  an 
  Analytic 
  Agent," 
  Roy. 
  Inst 
  , 
  April 
  1, 
  1898, 
  pp. 
  7 
  and 
  8. 
  

  

  