﻿28 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  Sandy 
  soils 
  contain 
  more 
  abundant 
  air 
  spaces 
  than 
  compact 
  

   clays, 
  and 
  in 
  clayey 
  regim 
  is 
  one 
  important 
  reason 
  for 
  deep 
  and 
  

   thorough 
  cultivation 
  of 
  the 
  soil 
  is 
  t<> 
  insure 
  the 
  free 
  access 
  of 
  

  

  ah 
  1 
  to 
  the 
  roots 
  of 
  crops. 
  

  

  26. 
  Water 
  supply 
  of 
  earth 
  roots. 
  

   It 
  is 
  known 
  to 
  most 
  people 
  that 
  or- 
  

   dinary 
  plants 
  must 
  absorb 
  tlirough 
  

   their 
  roots 
  a 
  good 
  deal 
  of 
  water. 
  If 
  

   house 
  plants 
  are 
  left 
  un 
  watered 
  for 
  

   two 
  or 
  three 
  days, 
  they 
  begin 
  to 
  

   wilt. 
  Field 
  crops 
  and 
  sometimes 
  

   even 
  shade 
  trees 
  do 
  the 
  same 
  in 
  

   times 
  of 
  severe 
  drought. 
  Many 
  

   plants, 
  when 
  grown 
  in 
  dry 
  ground, 
  

   will 
  flower 
  and 
  seed 
  in 
  a 
  dwarfed 
  

   condition. 
  The 
  common 
  groundsel, 
  

   a 
  weed 
  not 
  infrequently 
  found 
  in 
  

   long-tilled 
  fields 
  and 
  about 
  door- 
  

   yards 
  ( 
  lig. 
  19), 
  under 
  favorable 
  

   conditions 
  grows 
  to 
  be 
  a 
  foot 
  01 
  

   more 
  in 
  height, 
  but 
  in 
  the 
  very 
  dry 
  

   sand 
  along 
  Mediterranean 
  beaches 
  

   this 
  plant 
  flowers 
  and 
  seeds 
  when 
  

   only 
  an 
  inch 
  high. 
  

  

  27. 
  Roots 
  of 
  desert 
  plants. 
  The 
  

   plants 
  of 
  desert 
  and 
  other 
  dry 
  

   regions 
  frequently 
  show 
  striking 
  

   peculiarities 
  of 
  form 
  and 
  structure, 
  

   and 
  among 
  these 
  is 
  an 
  unusual 
  

   development 
  of 
  the 
  root 
  system. 
  

   Plants 
  able 
  to 
  live 
  under 
  extremely 
  

   dry 
  conditions 
  are 
  known 
  as 
  xero- 
  

  

  phijtes. 
  Familiar 
  examples 
  of 
  these 
  are 
  century 
  plants 
  and 
  cacti. 
  

   Some 
  xerophytes, 
  as 
  the 
  cacti, 
  have 
  a 
  rather 
  widely 
  spreading 
  

   root 
  system 
  extending 
  quite 
  near 
  the 
  surface 
  of 
  the 
  earth 
  ; 
  such 
  

   a 
  root 
  system 
  makes 
  the 
  most 
  of 
  every 
  one 
  of 
  the 
  infrequent 
  

  

  FIG. 
  19. 
  Effect 
  of 
  deficient 
  

   water 
  supply 
  on 
  growth 
  

  

  Tin- 
  plant 
  is 
  ijroiindsel, 
  a 
  common 
  

   European 
  weed 
  \vliicli 
  uro\Ys 
  t<> 
  

   from 
  lli 
  to 
  18 
  indies 
  hivji. 
  At 
  l> 
  

   is 
  shown 
  the 
  relative 
  height 
  ..f 
  

   the 
  saiiu- 
  plant 
  \\hen 
  t;n>\vn 
  in 
  

   very 
  dry 
  sands 
  along 
  Mediter- 
  

   ranean 
  beaches. 
  Modified 
  alter 
  

   " 
  Flora 
  Daiiica 
  " 
  

  

  