﻿INTRODUCTION 
  TO 
  BOTANY 
  

  

  Frequently 
  each 
  stoma 
  is 
  at 
  the 
  bottom 
  of 
  a 
  depression, 
  or 
  

   pit, 
  in 
  the 
  epidermis, 
  and 
  is 
  thus 
  somewhat 
  protected 
  from 
  

   drying 
  currents 
  of 
  air. 
  

  

  80. 
  Xerophytes. 
  Hants 
  like 
  the 
  cactus 
  (fig. 
  66), 
  the 
  desert 
  

   Pelargonium 
  (fig. 
  20), 
  the 
  crowbeny 
  (fig. 
  64), 
  and 
  a 
  multitude 
  

   of 
  others 
  (many 
  of 
  them 
  not 
  marked 
  by 
  any 
  such 
  peculiarities 
  

   of 
  form 
  and 
  structure 
  as 
  these 
  are), 
  which 
  can 
  resist 
  con- 
  

   ditions 
  of 
  extreme 
  drought, 
  are 
  called 
  ./<r<y<////^'.s'. 
  The 
  onlv 
  wav 
  

  

  in 
  which 
  one 
  can 
  get 
  

   a 
  good 
  idea 
  of 
  the 
  

  

  o 
  

  

  difference 
  between 
  

   xerophytes 
  and 
  ordi- 
  

   nary 
  plants, 
  or 
  meso- 
  

   jiliiitf*. 
  intheirpower 
  

   to 
  endure 
  a 
  combi- 
  

   nation 
  of 
  high 
  tem- 
  

   perature 
  and 
  scanty 
  

   Avater 
  supply 
  is 
  to 
  

   compare 
  their 
  behav- 
  

   ior 
  under 
  conditions 
  

   of 
  drought. 
  A 
  potted 
  

   plant 
  such 
  as 
  a 
  cactus 
  

   or 
  a 
  houseleek 
  for 
  a 
  

   representative 
  xero- 
  

   pliyte, 
  and 
  a 
  young 
  

   bean 
  plant 
  or 
  mus- 
  

   tard 
  plant 
  for 
  a 
  typical 
  mesophyte, 
  it' 
  left 
  unwatered, 
  will 
  afford 
  

   material 
  for 
  a 
  highly 
  profitable 
  comparison 
  of 
  types. 
  

  

  Are 
  any 
  xerophytes 
  of 
  economic 
  value? 
  any 
  mesophytes? 
  

   any 
  water 
  or 
  marsh 
  plants? 
  (Jive 
  as 
  many 
  examples 
  as 
  

   possible. 
  

  

  81. 
  Advantage 
  of 
  shedding 
  leaves. 
  When 
  the 
  soil 
  tempera- 
  

   ture 
  is 
  nearly 
  at 
  the 
  freezing 
  point, 
  most 
  plants 
  are 
  unable 
  to 
  

   absorb 
  much 
  water 
  by 
  their 
  roots. 
  It 
  is 
  probably 
  owing 
  mainly 
  

   to 
  this 
  fact 
  that 
  our 
  ordinary 
  irintcr 
  <l<;-'nlnnnx 
  trees 
  have 
  their 
  

   habit 
  of 
  shedding 
  their 
  leaves 
  at 
  the 
  approach 
  of 
  winter. 
  If 
  

  

  Euphorbia 
  splendciis 
  

  

  Hit 
  is 
  rather 
  leafy 
  when 
  well 
  

   applied 
  with 
  water 
  hut 
  nearly 
  leaf- 
  

   when 
  forced 
  to 
  live 
  with 
  a 
  

   very 
  scanty 
  water 
  supply 
  

  

  less 
  

  

  