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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  by 
  the 
  grape 
  leaf, 
  until 
  the 
  fungus 
  permeates 
  the 
  entire 
  leaf. 
  

   If 
  the 
  leaf 
  is 
  not 
  able 
  to 
  make 
  a 
  surplus 
  of 
  food 
  material, 
  the 
  

   amount 
  taken 
  by 
  the 
  parasite 
  may 
  result 
  in 
  the 
  starvation 
  

  

  and 
  death 
  of 
  the 
  grape 
  leaf. 
  I'ossilily, 
  also, 
  the 
  parasite 
  may 
  

   excrete 
  substances 
  that 
  poison 
  the 
  host 
  plant. 
  

  

  Sprayed 
  

  

  every 
  

  

  2 
  Weeks 
  

  

  FIG. 
  187. 
  Experiments 
  in 
  destroying 
  potato 
  blight 
  

  

  Photograph 
  by 
  the 
  New 
  York 
  Agricultural 
  Experiment 
  Station 
  illustrating 
  the 
  

   results 
  of 
  spraying 
  potatoes 
  to 
  prevent 
  disease. 
  Those 
  that 
  were 
  not 
  sprayed 
  

   yielded 
  at 
  the 
  rate 
  of 
  ltd 
  bushels 
  per 
  acre 
  ; 
  those 
  sprayed 
  three 
  times 
  during 
  the 
  

   season 
  yielded 
  at 
  the 
  rate 
  of 
  .'!.">(>.} 
  bushels 
  per 
  acre 
  ; 
  those 
  sprayed 
  every 
  two 
  weeks 
  

   yielded 
  at 
  the 
  rale 
  of 
  I'.XO 
  bushels 
  per 
  acre. 
  In 
  other 
  experiments 
  the 
  results 
  are 
  

   even 
  better. 
  In 
  this 
  same 
  station, 
  during 
  the 
  year 
  I'.HU, 
  the 
  average 
  gain 
  per 
  aere 
  

   iu 
  the 
  yield 
  for 
  three 
  spray 
  in^s 
  is 
  I'.il 
  bushels, 
  and 
  the 
  gain 
  for 
  spraying 
  every 
  

  

  t 
  \\ 
  o 
  \\ 
  eel\S 
  is 
  lil'ill 
  bushels 
  

  

  228. 
  Reproduction 
  of 
  grape 
  mildew. 
  Sometimes 
  the 
  upright 
  

   brain-lies 
  of 
  aerial 
  hvph;e 
  of 
  grape 
  mildew 
  produce 
  rounded, 
  

   spore-like 
  bodies 
  (r<>n/<//it) 
  (tig. 
  186, 
  A). 
  When 
  these 
  eonidia 
  

   come 
  into 
  favorable 
  moisture 
  (rain 
  or 
  dew) 
  and 
  temperature, 
  

   they 
  divide, 
  each 
  one 
  forming 
  several 
  y.oospores 
  (Tig. 
  ISti, 
  /' 
  ). 
  

   The 
  eonidia, 
  therefore, 
  act 
  like 
  sporangia, 
  since 
  they 
  form 
  

   asexual 
  spores. 
  The 
  zoospore 
  may 
  swim 
  in 
  the 
  dew 
  or 
  rain 
  for 
  

  

  