﻿7.— 
  SOME 
  NOTES 
  ON 
  ATTEMPTS 
  TO 
  PRODUCE 
  IMMUNITY 
  FROM 
  

   INSECT 
  ATTACK 
  ON 
  TEA. 
  

  

  By 
  E. 
  A. 
  Andrews, 
  B.A., 
  Entomologist 
  to 
  the 
  Indian 
  Tea 
  Association, 
  

  

  Mention 
  has 
  been 
  made, 
  at 
  previous 
  Meetings, 
  of 
  the 
  correlations 
  

   which 
  have 
  been 
  found 
  to 
  exist, 
  in 
  the 
  case 
  of 
  tea, 
  between 
  the 
  nature 
  

   of 
  the 
  environment 
  and 
  the 
  degree 
  of 
  liability 
  to 
  attack 
  by 
  insect 
  pests, 
  

   and 
  by 
  Helopeltis 
  theivora, 
  the 
  tea 
  mosquito, 
  in 
  particular. 
  The 
  apparent 
  

   importance 
  of 
  the 
  relative 
  amounts 
  of 
  potash 
  and 
  phosphoric 
  acid, 
  pre- 
  

   sent 
  in 
  the 
  soil 
  in 
  an 
  available 
  form, 
  and 
  of 
  the 
  relative 
  amounts 
  of 
  the 
  

   same 
  substances 
  in 
  the 
  leaves 
  before 
  and 
  after 
  Helopeltis 
  attack 
  has 
  also 
  

   been 
  discussed 
  and 
  accounts 
  have 
  been 
  given 
  of 
  various 
  manuring 
  experi- 
  

   ments 
  carried 
  out 
  with 
  a 
  view 
  to 
  increasing 
  the 
  relative 
  proportion 
  of 
  

   available 
  potash 
  in 
  the 
  soil 
  as 
  compared 
  with 
  phosphoric 
  acid, 
  in 
  the 
  

   hope 
  that 
  the 
  plants 
  would 
  thereby 
  absorb 
  a 
  larger 
  proportion 
  of 
  potash, 
  

   and 
  acquire 
  an 
  increased 
  resistance 
  to 
  attack 
  by 
  the 
  pest. 
  

  

  This 
  work 
  has 
  been 
  carried 
  further 
  since 
  the 
  last 
  Meeting, 
  both 
  

   in 
  the 
  direction 
  of 
  accumulating 
  evidence 
  to 
  corroborate 
  our 
  ideas 
  and 
  

   of 
  carrying 
  out 
  experiments 
  designed 
  to 
  increase 
  the 
  resistance 
  of 
  the 
  

   plants 
  to 
  attack 
  by 
  the 
  insect. 
  

  

  We 
  commence 
  with 
  the 
  fact, 
  founded 
  on 
  extensive 
  observation 
  and 
  

   experience, 
  that 
  comparative 
  immunity 
  from 
  Helopeltis 
  attack 
  not 
  only 
  

   can, 
  but 
  does, 
  occur 
  in 
  nature. 
  In 
  our 
  attempts 
  to 
  produce 
  immunity, 
  

   we 
  are 
  attempting 
  to 
  discover 
  and 
  reproduce 
  the 
  conditions 
  under 
  which 
  

   this 
  immunity 
  occurs 
  in 
  nature. 
  The 
  conditions 
  affecting 
  the 
  question 
  

   are 
  considerably 
  complicated, 
  but 
  would 
  appear 
  to 
  be 
  bound 
  up 
  with 
  the 
  

   relative 
  proportions 
  of 
  potash 
  and 
  phosphoric 
  acid 
  taken 
  up 
  from 
  the 
  

   soil 
  by 
  the 
  plant. 
  This 
  is 
  controlled, 
  not 
  merely 
  by 
  a 
  difference 
  in 
  the 
  

   type 
  of 
  soil, 
  but 
  by 
  difference 
  in 
  the 
  physical 
  and 
  chemical 
  condition 
  of 
  

   the 
  same 
  soil. 
  Cases 
  have 
  been 
  investigated 
  in 
  which 
  the 
  same 
  soil, 
  

   under 
  different 
  treatment 
  with 
  regard 
  to 
  cultivation, 
  etc., 
  has 
  produced 
  

   bushes 
  which 
  show 
  differences 
  in 
  degree 
  of 
  liability 
  to 
  atta»k 
  by 
  

   Helopeltis. 
  These 
  investigations 
  have 
  so 
  far 
  shown 
  very 
  little, 
  but 
  the 
  

   importance 
  of 
  the 
  potash 
  phosphoric 
  acid 
  ratio 
  has 
  been 
  emphasized 
  by 
  

   the 
  results 
  of 
  analysis 
  of 
  leaf 
  plucked 
  from 
  bushes 
  which 
  were 
  throwing 
  

   off 
  the 
  attack 
  of 
  the 
  pest. 
  Cases 
  were 
  observed, 
  in 
  districts 
  as 
  remote 
  

   as 
  Sylhet 
  and 
  the 
  Duars, 
  in 
  which 
  bushes, 
  which 
  had 
  been 
  absolutely 
  

  

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