﻿SPECIAL 
  FUNCTIONS 
  AND 
  FORMS 
  OF 
  STEMS 
  87 
  

  

  like 
  that 
  of 
  the 
  May 
  apple 
  (fig. 
  69), 
  the 
  mints, 
  couch 
  grass, 
  and 
  

   many 
  other 
  plants, 
  and 
  some 
  stouter 
  kinds, 
  like 
  that 
  of 
  the 
  tril- 
  

   lium 
  and 
  Solomon's-seal, 
  are 
  known 
  as 
  rootstocks, 
  or 
  rhizomes. 
  

   The 
  very 
  short 
  shoots 
  with 
  disk-like 
  stems 
  and 
  a 
  covering 
  of 
  

   scales, 
  or 
  of 
  coatings 
  formed 
  by 
  thickened 
  bases 
  of 
  leaves 
  (famil- 
  

   iar 
  in 
  some 
  lilies, 
  the 
  tulip, 
  and 
  the 
  onion), 
  are 
  called 
  bulbs. 
  

   Much 
  like 
  bulbs, 
  except 
  that 
  the 
  stem 
  is 
  more 
  developed 
  and 
  that 
  

   the 
  scales 
  are 
  almost 
  lacking, 
  are 
  tubers, 
  like 
  those 
  of 
  the 
  Jeru- 
  

   salem 
  artichoke, 
  the 
  potato, 
  and 
  the 
  crocus. 
  1 
  The 
  potato 
  is 
  a 
  

   particularly 
  good 
  tuber 
  for 
  study, 
  as 
  it 
  has 
  well-defined 
  nodes 
  

   and 
  internodes 
  ; 
  the 
  buds 
  (eyes) 
  are 
  arranged 
  in 
  a 
  distinctly 
  

   spiral 
  manner 
  and 
  are 
  borne 
  in 
  the 
  axils 
  

   of 
  little 
  scales 
  which 
  represent 
  leaves, 
  

   and 
  not 
  infrequently 
  the 
  tuber 
  is 
  con- 
  

   siderably 
  branched. 
  

  

  85. 
  Reproduction 
  by 
  portions 
  of 
  the 
  

   stem. 
  Some 
  plants 
  naturally 
  reproduce 
  

   themselves 
  mainly 
  by 
  more 
  or 
  less 
  spe- 
  

   cialized 
  portions 
  of 
  the 
  stem, 
  and 
  in 
  a 
  

   cultivated 
  state 
  many 
  others 
  are 
  made 
  

   to 
  do 
  so. 
  There 
  are 
  numerous 
  kinds, 
  

   such 
  as 
  the 
  potato, 
  the 
  strawberry, 
  the 
  

   banana, 
  and 
  most 
  lilies, 
  that 
  are 
  almost 
  

   always 
  propagated 
  by 
  some 
  sort 
  of 
  stem 
  

   or 
  shoot. 
  

  

  Many 
  plants 
  bear 
  small 
  aerial 
  bulbs 
  

   or 
  tubers 
  on 
  some 
  portion 
  of 
  the 
  stem 
  

   and 
  are 
  commonly 
  reproduced 
  by 
  these. 
  

   Familiar 
  examples 
  among 
  cultivated 
  

   plants 
  are 
  the 
  onion 
  and 
  the 
  tiger 
  lily. 
  

  

  The 
  bulblets 
  known 
  as 
  onion 
  sets 
  are 
  for 
  sale 
  at 
  every 
  seed 
  

   store, 
  and 
  in 
  some 
  parts 
  of 
  the 
  country 
  are 
  almost 
  exclusively 
  

   planted 
  by 
  onion 
  growers, 
  while 
  in 
  other 
  sections 
  the 
  seed 
  is 
  

   more 
  generally 
  planted. 
  The 
  black 
  bulblets 
  of 
  the 
  tiger 
  lily 
  

  

  1 
  Such 
  very 
  short 
  underground 
  stems 
  as 
  that 
  of 
  the 
  jack-in-the-pulpit 
  and 
  

   the 
  crocus 
  are 
  often 
  called 
  corms. 
  

  

  FIG. 
  70. 
  A 
  potato 
  seed- 
  

   ling 
  ten 
  weeks 
  old 
  

  

  cot, 
  cotyledons; 
  .s<, 
  tuber- 
  

   bearing 
  underground 
  stems 
  ; 
  

   t, 
  very 
  small 
  tubers 
  ; 
  r, 
  

   root. 
  Three 
  fourths 
  natu- 
  

   ral 
  size. 
  After 
  Percival 
  

  

  