﻿76 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  74. 
  Excessive 
  illumination. 
  While 
  the 
  leaves 
  of 
  plants 
  

   growing 
  in 
  the 
  shade 
  often 
  suffer 
  from 
  lack 
  of 
  sunlight 
  and 
  

   are 
  usually 
  so 
  arranged 
  as 
  to 
  utilize 
  most 
  fully 
  what 
  light 
  

   there 
  is, 
  it 
  is 
  possible 
  for 
  leaves 
  in 
  exposed 
  situations 
  to 
  have 
  

   too 
  much 
  light. 
  It 
  seems 
  certain 
  that 
  the 
  most 
  powerful 
  sunlight 
  

  

  may 
  injure 
  the 
  chloroplasts 
  

   and 
  therefore 
  cripple 
  the 
  

   power 
  of 
  the 
  leaf 
  to 
  do 
  its 
  

   work 
  of 
  photosynthesis. 
  

  

  Compass 
  plants, 
  such 
  as 
  the 
  

   common 
  prairie 
  rosinweed 
  

   (fti/ji/tiiini') 
  and 
  the 
  prickly 
  

   lettuce, 
  have 
  leaves 
  some- 
  

   what 
  erect, 
  with 
  edges 
  di- 
  

   rected 
  nearly 
  north 
  and 
  south, 
  

   so 
  that 
  they 
  secure 
  good 
  il- 
  

   lumination 
  during 
  the 
  cooler 
  

   morning 
  and 
  evening 
  hours 
  

   1 
  mt 
  present 
  the 
  leaves 
  nearly 
  

   edgeways 
  to 
  the 
  sun 
  at 
  noon. 
  

   Many 
  other 
  plants 
  maintain 
  

   some 
  or 
  all 
  of 
  their 
  leaves 
  in 
  a 
  

   nearly 
  vertical 
  position, 
  but 
  

   with 
  the 
  edges 
  not 
  directed 
  

   north 
  and 
  south. 
  In 
  the 
  olive 
  

  

  ia 
  creeper 
  (Psedem), 
  a 
  many 
  leaves 
  point 
  almost 
  ver- 
  

   U'ndril 
  climliiT 
  k 
  , 
  , 
  ., 
  . 
  , 
  

  

  tically 
  upward, 
  while 
  in 
  the 
  

  

  The 
  tendrils 
  are 
  modified 
  shoots. 
  At 
  a 
  they 
  . 
  f 
  

  

  are 
  seen 
  fast,n,,l 
  . 
  a 
  twig 
  and 
  at 
  I. 
  adher- 
  Commonest 
  SpCClCS 
  of 
  

   inj, 
  r 
  strongly 
  by 
  means 
  of 
  their 
  expanded, 
  JyjrfHS 
  (fig. 
  GO) 
  the 
  

  

  disk-like 
  tips 
  to 
  the 
  surface 
  of 
  a 
  wall 
  , 
  . 
  ,, 
  -i 
  i 
  

  

  hang 
  vertically 
  downward. 
  

  

  In 
  a 
  great 
  number 
  of 
  trees 
  the 
  young 
  leaves 
  from 
  recently 
  

   opened 
  buds 
  stand 
  erect 
  or 
  hang 
  straight 
  down. 
  In 
  one 
  

   tropical 
  species 
  1 
  the 
  illumination 
  received 
  by 
  these 
  young 
  

   drooping 
  leaves 
  is 
  not 
  more 
  than 
  one 
  five 
  hundredth 
  as 
  intense 
  

   as 
  that 
  received 
  by 
  the 
  most 
  exposed 
  of 
  the 
  mature 
  leaves. 
  

   1 
  Amherstia 
  nobilis, 
  from 
  Burma. 
  

  

  FIG. 
  r,<.. 
  

  

  