﻿264 
  MacDougal: 
  Growth 
  of 
  the 
  tomato 
  

  

  on 
  maturity. 
  In 
  both 
  types 
  of 
  growth 
  the 
  rate 
  depends 
  upon, 
  or 
  

   is 
  influenced 
  by, 
  the 
  amount 
  of 
  growth 
  that 
  has 
  previously 
  taken 
  

   place, 
  as 
  has 
  been 
  demonstrated 
  by 
  Reed 
  in 
  his 
  measurements 
  of 
  

  

  ■ 
  

  

  growth 
  of 
  the 
  stems 
  of 
  apricot 
  trees. 
  

  

  The 
  stems 
  of 
  the 
  tomato 
  are 
  enlarging 
  during 
  the 
  growth 
  of 
  

   the 
  fruits, 
  the 
  leaf 
  surfaces 
  are 
  increasing 
  and 
  the 
  pedicels 
  of 
  the 
  

   fruits 
  show 
  an 
  increasing 
  cross 
  section, 
  so 
  that 
  not 
  only 
  is 
  an 
  

  

  ■ 
  

  

  additional 
  amount 
  of 
  water 
  and 
  material 
  available 
  but 
  its 
  trans- 
  

   location 
  may 
  be 
  facilitated. 
  

  

  It 
  would 
  be 
  erroneous 
  however 
  to 
  consider 
  the 
  fruits 
  as 
  reser- 
  

   voirs 
  which 
  passively 
  receive 
  the 
  solutions 
  poured 
  into 
  them 
  

   through 
  the 
  stems. 
  The 
  fruits 
  are 
  in 
  fact 
  largely 
  made 
  up 
  of 
  

   rapidly 
  enlarging 
  masses 
  of 
  thin-walled 
  cells 
  which 
  control 
  absorp- 
  

   tion 
  of 
  material 
  as 
  occurs 
  in 
  living 
  tissues. 
  Liquids 
  are 
  drawn 
  

   into 
  these 
  cells, 
  not 
  forced. 
  

  

  The 
  forces 
  which 
  operate 
  to 
  carry 
  water 
  and 
  solid 
  material 
  

   into 
  a 
  fruit 
  may 
  be 
  grouped 
  under 
  osmosis 
  and 
  imbibition. 
  

  

  The 
  freely 
  soluble 
  sugars 
  which 
  constitute 
  about 
  9 
  per 
  cent 
  of 
  

   the 
  dry 
  weight 
  of 
  young 
  fruits 
  and 
  38 
  per 
  cent 
  of 
  ripe 
  fruits, 
  

   according 
  to 
  the 
  analyses 
  of 
  Albahary, 
  would 
  operate 
  to 
  set 
  up 
  and 
  

   maintain 
  a 
  turgidity 
  that 
  would 
  probably 
  reach 
  eight 
  to 
  twelve 
  

  

  r 
  

  

  atmospheres, 
  and 
  the 
  attractive 
  force 
  of 
  these 
  substances 
  would 
  

   be 
  one 
  of 
  the 
  main 
  factors 
  in 
  drawing 
  material 
  into 
  the 
  fruits. 
  

  

  t 
  

  

  It 
  is 
  well 
  known, 
  however, 
  that 
  fruits 
  may 
  withdraw 
  water 
  

   from 
  stems 
  that 
  are 
  relatively 
  drier, 
  and 
  that 
  roots 
  may 
  take 
  up 
  

   water 
  from 
  soils 
  in 
  which 
  the 
  osmotic 
  action 
  would 
  be 
  greater. 
  

   To 
  account 
  for 
  such 
  action 
  we 
  must 
  look 
  to 
  imbibition, 
  the 
  phe- 
  

   nomena 
  by 
  which 
  colloidal 
  matter, 
  such 
  as 
  jelly 
  or 
  wood, 
  absorbs 
  

   water 
  or 
  solutions 
  and 
  swells 
  as 
  a 
  consequence 
  of 
  the 
  hydration 
  or 
  

   addition 
  of 
  molecules 
  of 
  water 
  to 
  the 
  aggregates 
  of 
  molecules 
  of 
  

   solid 
  matter 
  in 
  their 
  intimate 
  structure, 
  for 
  growth 
  under 
  such 
  

   circumstances. 
  

  

  Extensive 
  investigations 
  at 
  the 
  Desert 
  Laboratory 
  show 
  that 
  

   the 
  living 
  matter 
  of 
  plants 
  is 
  a 
  mixture 
  of 
  albuminous 
  substances 
  

  

  ( 
  

  

  and 
  of 
  pentosans 
  or 
  mucilages. 
  Furthermore, 
  parallel 
  experiments 
  

  

  with 
  mixtures 
  made 
  In 
  the 
  laboratory 
  show 
  that 
  in 
  taking 
  up 
  water 
  

  

  the 
  plant 
  behaves 
  like 
  a 
  sac 
  containing 
  albumin 
  and 
  mucilages. 
  

  

  * 
  It 
  IS 
  necessary 
  for 
  a 
  clear 
  understanding 
  of 
  the 
  action 
  of 
  the 
  

  

  