﻿SPECIAL 
  FUNCTIONS 
  AND 
  FORMS 
  OF 
  STEMS 
  89 
  

  

  Underground 
  stems 
  of 
  various 
  kinds 
  are 
  so 
  common 
  as 
  

   means 
  of 
  reproduction 
  that 
  only 
  a 
  very 
  few 
  of 
  them 
  need 
  be 
  

   mentioned. 
  Some 
  of 
  the 
  worst 
  weeds 
  are 
  those 
  which 
  have 
  

   running 
  rootstocks, 
  

   like 
  the 
  nut 
  grass 
  

   {Cyperus), 
  which 
  

   produces 
  many 
  lit- 
  

   tle 
  tubers, 
  each 
  of 
  

   which 
  may 
  grow 
  

   into 
  a 
  new 
  plant, 
  

   and 
  the 
  couch 
  

   grass 
  (Chapter 
  XX) 
  

   and 
  Canada 
  thistle, 
  

   which 
  may 
  be 
  cut 
  

   up 
  by 
  the 
  hoe 
  

   and 
  produce 
  a 
  new 
  

   plant 
  from 
  every 
  

   node. 
  Among 
  cul- 
  

   tivated 
  plants 
  a 
  

   great 
  number 
  of 
  the 
  

   earliest 
  blooming 
  

   herbaceous 
  kinds, 
  

   such 
  as 
  squills, 
  

   hyacinths, 
  tulips, 
  

   crocuses, 
  and 
  snow- 
  

   drops, 
  are 
  grown 
  

   from 
  bulbs 
  or 
  other 
  

   forms 
  of 
  under- 
  

   ground 
  stem. 
  The 
  

   commonest 
  of 
  all 
  

   instances 
  of 
  propa- 
  

   gation 
  by 
  this 
  kind 
  

   of 
  stem 
  is 
  that 
  of 
  the 
  potato 
  (figs. 
  70 
  and 
  71), 
  which 
  is 
  never 
  

   grown 
  from 
  seed 
  except 
  for 
  the 
  production 
  of 
  new 
  varieties. 
  

   As 
  every 
  farmer 
  and 
  market 
  gardener 
  knows, 
  each 
  potato 
  

   will 
  produce 
  as 
  many 
  new 
  plants 
  as 
  it 
  has 
  buds, 
  or 
  eyes, 
  

  

  FIG. 
  72. 
  A 
  black 
  raspberry 
  plant 
  reproducing 
  by 
  

   a 
  natural 
  stolon 
  

  

  At 
  A, 
  the 
  original 
  root 
  system 
  ; 
  at 
  B, 
  a 
  newly 
  formed 
  

   root 
  system 
  with 
  a 
  young 
  shoot 
  sh. 
  Much 
  reduced 
  and 
  

   somewhat 
  diagrammatic. 
  The 
  arch 
  is 
  really 
  much 
  

   flatter 
  and 
  the 
  dying 
  portion 
  of 
  the 
  stem, 
  aa' 
  ', 
  propor- 
  

   tionally 
  five 
  or 
  ten 
  times 
  as 
  long 
  as 
  here 
  shown 
  

  

  