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  Fluctuations 
  

  

  growing, 
  but 
  sooner 
  or 
  later 
  reaches 
  a 
  maximum 
  

   and 
  may 
  afterwards 
  decrease. 
  

  

  This 
  periodic 
  augmentation 
  and 
  declination 
  is 
  

   often 
  boldly 
  manifest, 
  though 
  in 
  other 
  cases 
  it- 
  

   may 
  be 
  hidden 
  by 
  the 
  effect 
  of 
  alternate 
  influ- 
  

   ences. 
  Pinnate 
  leaves 
  generally 
  have 
  their 
  

   lower 
  blades 
  smaller 
  than 
  the 
  upper 
  ones, 
  the 
  

   longest 
  being 
  seen 
  sometimes 
  near 
  the 
  apex 
  

   and 
  sometimes 
  at 
  a 
  distance 
  from 
  it. 
  Branches 
  

   bearing 
  their 
  leaves 
  in 
  two 
  rows 
  often 
  afford 
  

   quite 
  as 
  obvious 
  examples, 
  and 
  shoots 
  in 
  gen- 
  

   eral 
  comply 
  with 
  the 
  same 
  rule. 
  Germinating 
  

   plants 
  are 
  very 
  easy 
  of 
  observation 
  on 
  this 
  

   point. 
  When 
  they 
  are 
  very 
  weak 
  they 
  produce 
  

   only 
  small 
  leaves. 
  But 
  their 
  strength 
  gradually 
  

   increases 
  and 
  the 
  subsequent 
  organs 
  reach 
  

   fuller 
  dimensions 
  until 
  the 
  maximum 
  is 
  at- 
  

   tained. 
  The 
  phenomenon 
  is 
  so 
  common 
  that 
  its 
  

   importance 
  is 
  usually 
  overlooked. 
  It 
  should 
  be 
  

   considered 
  as 
  only 
  one 
  instance 
  of 
  a 
  rule, 
  which 
  

   holds 
  good 
  for 
  all 
  stems 
  and 
  all 
  branches, 
  and 
  

   which 
  is 
  everywhere 
  dependent 
  on 
  the 
  relation 
  

   of 
  growth 
  to 
  nutrition. 
  

  

  The 
  rule 
  of 
  periodicity 
  not 
  only 
  affects 
  the 
  

   size 
  of 
  the 
  organs, 
  but 
  also 
  their 
  number, 
  when- 
  

   ever 
  these 
  are 
  largely 
  variable. 
  Umbellate 
  

   plants 
  have 
  numerous 
  rays 
  on 
  the 
  umbels 
  of 
  

   strong 
  stems, 
  but 
  the 
  number 
  is 
  seen 
  to 
  decrease 
  

   and 
  to 
  become 
  very 
  small 
  on 
  the 
  weakest 
  lateral 
  

  

  