﻿THE 
  SEED 
  PLANTS 
  

  

  303 
  

  

  sir 
  

  

  While 
  these 
  developments 
  have 
  been 
  taking 
  place 
  in 
  the 
  

   embryo 
  sac, 
  the 
  integument 
  walls 
  have 
  become 
  dry 
  and 
  hard, 
  

   so 
  that, 
  by 
  the 
  time 
  the 
  young 
  plant 
  has 
  differentiated 
  the 
  

   root, 
  stem, 
  and 
  leaf 
  regions, 
  it 
  is 
  usually 
  inclosed 
  by 
  hard 
  

   and 
  dry 
  walls, 
  and 
  the 
  whole 
  structure 
  is 
  a 
  seed. 
  In 
  some 
  

   cases 
  the 
  seed 
  is 
  dropped 
  

   from 
  the 
  parent 
  plant 
  at 
  

   once, 
  and 
  may 
  begin 
  its 
  

   growth 
  immediately. 
  Seeds 
  

   may 
  lie 
  dormant 
  on 
  the 
  

   ground 
  until 
  the 
  return 
  

   of 
  spring, 
  or 
  may 
  in 
  some 
  

   cases 
  lie 
  dormant 
  for 
  sev- 
  

   eral 
  years, 
  and 
  still 
  retain 
  

   their 
  vitality. 
  The 
  seeds 
  of 
  

   the 
  cocklebur 
  and 
  of 
  some 
  

   desert 
  plants 
  may 
  lie 
  in 
  the 
  

   ground 
  for 
  several 
  years 
  

   and 
  then 
  grow. 
  The 
  seed 
  

   coats 
  sometimes 
  become 
  so 
  

   dry 
  and 
  hard 
  that 
  the 
  water 
  

   and 
  air 
  necessary 
  for 
  ger- 
  

   mination 
  cannot 
  penetrate, 
  

   and 
  this 
  condition 
  remains 
  

   until, 
  through 
  decay 
  of 
  the 
  

   wall 
  or 
  through 
  injury 
  to 
  

   it, 
  the 
  needed 
  materials 
  can 
  

   get 
  into 
  the 
  seed. 
  Most 
  

   seeds, 
  such 
  as 
  wheat, 
  corn, 
  

   and 
  oats, 
  lose 
  their 
  vitality 
  within 
  a 
  few 
  years 
  at 
  the 
  most. 
  

  

  288. 
  The 
  fruit. 
  The 
  relations 
  between 
  seed 
  and 
  fruit 
  are 
  

   not 
  easily 
  denned, 
  for 
  the 
  reason 
  that 
  the 
  fruit 
  may 
  include 
  

   a 
  few 
  or 
  many 
  structures. 
  The 
  ripened 
  ovule 
  containing 
  the 
  

   embryo 
  is 
  the 
  seed. 
  Sometimes 
  structures 
  other 
  than 
  the 
  seed 
  

   ripen 
  with 
  it 
  ; 
  regardless 
  of 
  how 
  many 
  things 
  ripen 
  with 
  the 
  

   seed, 
  all 
  are 
  included 
  in 
  the 
  term 
  fruit. 
  In 
  the 
  sunflower 
  the 
  

  

  -esw 
  

  

  suspc 
  

  

  - 
  in 
  int 
  

  

  ou 
  int 
  

  

  FIG. 
  232. 
  Diagram 
  of 
  the 
  ovule, 
  embryo 
  

  

  sac, 
  and 
  embryo 
  of 
  the 
  shepherd's-purse 
  

  

  (Capsella 
  Bursa-pastoris) 
  

  

  The 
  parts 
  shown 
  are 
  the 
  outer 
  integument 
  

   (ou 
  int), 
  inner 
  integument 
  (in 
  int), 
  embryo- 
  

   sac 
  wall 
  (e 
  s 
  w), 
  suspensor 
  cells 
  (susj) 
  c), 
  

   root 
  region 
  (r 
  r), 
  stem 
  region 
  (st 
  r), 
  and 
  

   seed 
  leaves 
  (s 
  I) 
  

  

  