﻿352 
  Dr. 
  S. 
  R. 
  Milner 
  on 
  the 
  Effect 
  of 
  

  

  reduced 
  to 
  a 
  very 
  small 
  amount. 
  Each 
  stoma 
  is 
  fully 
  efficient 
  

   in 
  proportion 
  to 
  its 
  radius 
  ; 
  but 
  the 
  output 
  will 
  be 
  diminished 
  

   for 
  all 
  sizes 
  of 
  stoma 
  because 
  it 
  has 
  to 
  transpire 
  into 
  a 
  

   nearly 
  saturated 
  space. 
  When 
  the 
  stoma 
  becomes 
  constricted 
  

   it 
  operates 
  more 
  feebly, 
  but 
  under 
  better 
  conditions 
  ; 
  if 
  a 
  

   circular 
  stomatal 
  aperture 
  of 
  dimensions 
  as 
  above 
  is 
  con- 
  

   stricted 
  to 
  -f 
  of 
  its 
  radius, 
  its 
  own 
  resistance 
  will 
  be 
  half 
  the 
  

   total 
  resistance 
  to 
  transpiration 
  instead 
  of 
  only 
  J 
  ; 
  if 
  it 
  is 
  

   constricted 
  to 
  -gL-, 
  the 
  resistance 
  of 
  the 
  stoma 
  itself 
  will 
  be 
  

   | 
  of 
  the 
  whole, 
  and 
  the 
  layer 
  of 
  moist 
  air 
  outside 
  will 
  hardly 
  

   count. 
  The 
  question 
  is 
  whether 
  we 
  can 
  assume 
  a 
  still 
  layer 
  

   of 
  air 
  anything 
  like 
  I 
  mm. 
  thick. 
  As 
  moist 
  air 
  is 
  sensibly 
  

   lighter 
  than 
  dry, 
  such 
  a 
  layer 
  could 
  hardly 
  be 
  established 
  if 
  

   the 
  leaf 
  itself 
  is 
  not 
  quite 
  still, 
  unless 
  possibly 
  to 
  some 
  degree 
  

   on 
  the 
  lower 
  surface 
  of 
  a 
  horizontal 
  leaf. 
  

  

  The 
  problem 
  whether 
  a 
  cause 
  like 
  this, 
  which 
  I 
  take 
  to 
  be 
  

   the 
  essence 
  of 
  Dr. 
  Jeffreys^ 
  important 
  suggestion, 
  has 
  really 
  

   intervened 
  in 
  observations 
  such 
  as 
  those 
  quoted 
  by 
  Darwin 
  

   from 
  F. 
  E. 
  Lloyd 
  (p. 
  277) 
  could 
  only 
  be 
  probed 
  by 
  further 
  

   experiment 
  under 
  suitable 
  precautions. 
  

  

  The 
  question 
  whether 
  the 
  sap-current 
  in 
  trees 
  is 
  reduced 
  

   on 
  still 
  days 
  is 
  much 
  simpler, 
  for 
  the 
  whole 
  region 
  of 
  the 
  

   tree-top 
  may 
  become 
  nearly 
  saturated. 
  

  

  These 
  considerations, 
  which 
  apply 
  to 
  the 
  transpiration 
  of 
  

   vapour 
  from 
  the 
  stomata, 
  are 
  pertinent, 
  of 
  course, 
  equally 
  

   to 
  the 
  diffusion 
  of 
  carbon 
  dioxide 
  into 
  them. 
  They 
  seem 
  

   directly 
  to 
  confirm, 
  from 
  a 
  different 
  aspect, 
  the 
  conclusions 
  

   of 
  Brown 
  and 
  Escombe 
  that 
  the 
  stomatal 
  cavities 
  are 
  

   capable 
  of 
  much 
  more 
  absorption 
  than 
  they 
  are 
  called 
  upon 
  

   to 
  perform. 
  

  

  Cambridge, 
  March 
  9. 
  

  

  XXXIX. 
  The 
  Effect 
  of 
  Interionic 
  Force 
  in 
  Electrolytes. 
  

   By 
  S. 
  R. 
  Milner, 
  D.Sc* 
  

  

  Part 
  II. 
  

   Ionic 
  Mobility 
  and 
  Osmotic 
  Pressure. 
  

  

  THE 
  first 
  attempt 
  to 
  determine 
  the 
  effect 
  of 
  interionic 
  

   force 
  on 
  the 
  ionic 
  mobility 
  is 
  due 
  to 
  Sutherland 
  f, 
  

   whose 
  method 
  is 
  based 
  on 
  the 
  following 
  idea 
  : 
  — 
  The 
  effect 
  of 
  

   the 
  forces 
  will 
  approximate 
  to 
  what 
  would 
  be 
  obtained 
  if 
  the 
  

   ions 
  were 
  regularly 
  distributed 
  throughout 
  the 
  liquid, 
  say 
  

   at 
  the 
  centres 
  of 
  equal 
  cubes. 
  When 
  they 
  are 
  displaced 
  

  

  * 
  Communicated 
  by 
  the 
  Author, 
  

   t 
  Phil. 
  Mag. 
  xiv. 
  p. 
  1 
  (1907). 
  

  

  