﻿FUNGI 
  AND 
  FUNGOUS 
  DISEASES 
  OF 
  PLANTS 
  241 
  

  

  fifteen 
  or 
  twenty 
  minutes, 
  and 
  then 
  lose 
  its 
  cilia 
  and 
  begin 
  to 
  

   grow 
  into 
  a 
  new 
  hypha 
  of 
  the 
  mildew. 
  These 
  new 
  hyphse 
  

   may 
  grow 
  through 
  the 
  stomata 
  of 
  leaves 
  and 
  start 
  a 
  new 
  

   growth 
  of 
  the 
  parasite. 
  

  

  Within 
  the 
  host 
  leaf 
  sexual 
  reproduction 
  of 
  the 
  parasite 
  

   occurs, 
  and 
  oospores 
  (fig. 
  186, 
  C') 
  are 
  formed. 
  These 
  oospores 
  

   are 
  thought 
  to 
  reproduce 
  the 
  parasite 
  in 
  the 
  following 
  spring, 
  

   when 
  the 
  decay 
  of 
  the 
  host 
  leaf 
  releases 
  them. 
  Our 
  knowledge 
  

   of 
  oospore 
  formation 
  in 
  grape 
  mildew 
  and 
  potato 
  blight 
  is 
  still 
  

   incomplete. 
  It 
  is 
  thought, 
  however, 
  by 
  some 
  special 
  students 
  

   of 
  fungi, 
  that 
  potato 
  blight 
  has 
  largely 
  lost 
  its 
  power 
  of 
  sexual 
  

   reproduction, 
  and 
  that 
  oospores 
  are 
  not 
  often 
  formed. 
  1 
  

  

  229. 
  Prevention 
  of 
  grape 
  mildew 
  and 
  potato 
  blight. 
  Potato 
  

   blight 
  is 
  a 
  common 
  and 
  extremely 
  destructive 
  potato 
  disease 
  

   caused 
  by 
  a 
  fungus 
  that 
  resembles 
  grape 
  mildew 
  in 
  its 
  structure 
  

   and 
  habits 
  of 
  growth. 
  It 
  is 
  readily 
  and 
  widely 
  distributed 
  and 
  

   often 
  causes 
  serious 
  losses 
  by 
  partially 
  or 
  almost 
  completely 
  

   preventing 
  the 
  growth 
  of 
  a 
  potato 
  crop. 
  Both 
  potato 
  blight 
  

   and 
  grape 
  mildew 
  are 
  prevented 
  from 
  reaching 
  their 
  normal 
  

   growth, 
  and 
  are 
  sometimes 
  completely 
  destroyed, 
  by 
  spraying 
  

   with 
  Bordeaux 
  mixture. 
  2 
  It 
  was 
  in 
  connection 
  with 
  a 
  study 
  of 
  

   grape 
  mildew 
  that 
  the 
  Frenchman 
  Millardet, 
  in 
  1881, 
  began 
  

   experimenting 
  with 
  Bordeaux 
  mixtures. 
  He 
  demonstrated 
  the 
  

   fact 
  that 
  this 
  mixture, 
  when 
  properly 
  used 
  as 
  a 
  spray, 
  will 
  pre- 
  

   vent 
  most 
  of 
  the 
  ill 
  effects 
  of 
  grape 
  mildew. 
  The 
  effect 
  of 
  

   using 
  this 
  spray 
  in 
  treating 
  potatoes 
  is 
  well 
  shown 
  in 
  figure 
  187. 
  

   Many 
  other 
  destructive 
  parasitic 
  diseases 
  of 
  plants, 
  though 
  by 
  

   no 
  means 
  all 
  of 
  them, 
  may 
  be 
  prevented 
  in 
  the 
  same 
  way. 
  3 
  

  

  1 
  G. 
  P. 
  Clinton, 
  "Oospores 
  of. 
  Potato 
  Blight," 
  Science, 
  744-747, 
  1911. 
  

  

  2 
  The 
  preparation 
  as 
  most 
  commonly 
  used 
  consists 
  of 
  materials 
  mixed 
  in 
  

   the 
  following 
  proportions 
  : 
  copper 
  sulphate, 
  5 
  pounds 
  ; 
  stone 
  lime, 
  5 
  pounds 
  ; 
  

   water, 
  50 
  gallons. 
  Other 
  proportions 
  are 
  often 
  used, 
  as 
  indicated 
  in 
  agri- 
  

   cultural 
  experiment 
  station 
  reports. 
  

  

  3 
  Duggar, 
  B. 
  M., 
  Fungous 
  Diseases 
  of 
  Plants. 
  Ginn 
  and 
  Company, 
  

   Boston, 
  1909. 
  

  

  " 
  Potato 
  Spraying 
  Experiments 
  in 
  1906," 
  Bulletin 
  279, 
  N.Y. 
  Agr. 
  Exp. 
  Sta. 
  

   "Certain 
  Potato 
  Diseases 
  and 
  their 
  Remedies," 
  Bulletin 
  72, 
  Vt. 
  Agr. 
  

   Exp. 
  Sta. 
  

  

  