﻿72 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  shrubs 
  and 
  trees, 
  besides 
  those 
  already 
  mentioned, 
  are 
  the 
  

   lilacs, 
  the 
  ashes, 
  the 
  horse-chestnut, 
  and 
  the 
  buckeyes. 
  Many 
  

   kinds 
  of 
  spirals 
  occur, 
  the 
  simplest 
  being 
  that 
  of 
  Indian 
  corn, 
  

   in 
  which 
  the 
  leaves 
  stand 
  in 
  two 
  rows 
  along 
  the 
  stem, 
  the 
  

  

  third 
  directly 
  above 
  the 
  first, 
  the 
  second 
  

   a 
  hove 
  the 
  fourth, 
  and 
  so 
  on. 
  

  

  70. 
  Importance 
  of 
  leaf 
  arrangement. 
  

   The 
  photosynthetic 
  work 
  of 
  ordinary 
  

   leafy 
  plants 
  is 
  run 
  by 
  sun 
  power, 
  or 
  (to 
  

   put 
  it 
  more 
  technically) 
  is 
  due 
  to 
  the 
  

   energy 
  derived 
  from 
  the 
  sun 
  and 
  acting 
  

  

  FIG. 
  54. 
  Entire 
  plant 
  of 
  dog- 
  

   tooth 
  violet 
  (Erythroiihitn 
  ) 
  

  

  Hardly 
  any 
  aerial 
  stem 
  ap- 
  

   pears, 
  the 
  flower 
  stalk 
  bring 
  

   sheathed 
  by 
  the 
  leafstalks 
  

   and 
  arising 
  from 
  a 
  deeply 
  

   buried 
  bulb. 
  One 
  fourth 
  

   natural 
  size 
  

  

  FIG. 
  55. 
  Rosette 
  of 
  leaves 
  of 
  the 
  common 
  

  

  evening 
  primrose, 
  as 
  seen 
  at 
  the 
  end 
  of 
  the 
  

  

  first 
  year's 
  growth 
  of 
  the 
  plant 
  

  

  on 
  the 
  green 
  cells 
  of 
  the 
  leaf. 
  Clearly, 
  therefore, 
  it 
  is 
  usually 
  

   as 
  important 
  for 
  sugar- 
  and 
  starch-making 
  that 
  the 
  leaf 
  should 
  

   catch 
  all 
  the 
  sunlight 
  it 
  can 
  get, 
  as 
  it 
  is 
  for 
  rapid 
  sailing 
  that 
  

   a 
  sailboat 
  should 
  expose 
  its 
  sails 
  as 
  fairly 
  as 
  possible 
  to 
  the 
  

   wind. 
  1 
  The 
  student 
  will 
  find 
  it 
  well 
  worth 
  while 
  to 
  observe 
  

   the 
  arrangement 
  of 
  alternate 
  leaves, 
  which 
  are 
  so 
  placed, 
  both 
  

  

  1 
  Leaves 
  just 
  unfolding 
  from 
  the 
  bud. 
  some 
  of 
  those 
  exposed 
  to 
  tropical 
  

   suns, 
  and 
  certain 
  others 
  (sect. 
  51) 
  are 
  exceptions. 
  

  

  