Report  on  Wheat-Mildew. 
641 
velops  into  mycelium,  which  in  the  course,  &c.,  of  about  eight 
clays  produces  rusty  patches  on  both  the  upper  and  under  sides 
of  the  barberry -leaf.  From  these  spots  of  rust  two  different  kinds 
of  spore  are  shed,  CEcidinm-spores  from  the  under,  and  Sper- 
mogonia  from  the  upper  side  of  the  leaf ; and  it  is  supposed  by 
Mr.  Plowright  that  they  are  of  different  sexes,  the  smaller 
spores  or  Spermogonia  playing  the  part  of  the  male.  The 
CEcidium-spores  (perhaps  fertilized  by  the  Spermogonia ) are 
distributed  in  the  air  in  incalculable  numbers,  and  those  which 
fall  on  plants  adapted  to  fulfil  the  office  of  host-plants,  germinate 
under  favourable  atmospheric  conditions, — that  is  to  say,  in  damp 
weather, — and  throw  out  a germ  tube  which  enters  the  host- 
plant  through  one  of  its  stomata  or  breathing  pores.  Having 
effected  an  entrance,  mycelium  is  again  developed  in  the  tissue 
of  the  plant  (wheat  or  grass),  and  the  fungus  has  now  obtained 
possession  of  a home  in  which  it  can  complete  its  life  cycle.  In 
the  course  of  ten  or  twelve  days  Uredo-spores  are  produced  on 
the  outside  of  the  leaf.  These  are  distributed,  and  germinate 
and  reproduce  their  kind.  The  reproduction  of  Uredo  is  repeated 
generation  after  generation  until  the  host-plant  approaches 
maturity,  when  the  mycelium  throws  out  Teleuto-spores  or 
mildew,  and  the  life  cycle  is  completed. 
In  the  foregoing  account  the  identity  of  the  fungus  which 
produces  barberry-rust  with  that  which  afterwards  produces 
a rust  on  wheat,  and  eventually  mildew,  is  assumed  as  indis- 
putably proved.  There  are,  however,  circumstances  which  lead 
some  to  doubt  whether  the  barberry-tree  is  indispensable  for  the 
development  of  mildew.  Let  it  be  admitted  that  the  mildew- 
spores  will  germinate  on  the  barberry  and  produce  oecidium- 
spores,  which  will  germinate  on  wheat  and  other  grasses,  and 
there  generate  Uredo  and  Puccinia , does  it  follow  that  the  bar- 
berry is  the  only  plant  which  can  act  as  a foster-parent  ? 
The  advocates  of  the  barberry  theory  adduce  facts  to  prove 
that  mildew  is  particularly  prevalent  in  the  immediate  vicinity 
of  such  trees,  and  that  the  removal  of  them  has  at  once  caused 
a diminution  of  the  disease.* 
* Sir  Joseph  Banks,  in  the  ‘Annals  of  Agriculture,’  tells  of  a village  in  Norfolk 
“ where  barberries  abound  and  wheat  seldom  succeeds,  called  by  the  opprobrious 
appellation  of  Mildew  Eollesby  ” (xliii.  p 521) ; and  Cooke  and  Berkeley  in  their 
work  on ‘Fungi’  (King’s  Int.  Scientific  Series)  say  There  is  a village  in 
Norfolk,  called  Mildew  Rollesby,  because  of  its  unenviable  notoriety  in  days 
past  for  mildewed  corn,  produced  it  was  said  by  the  barberry  bushes,  which  were 
cut  down,  and  then  mildew  disappeared  from  the  corn  fields,  so  that  Rollesby  no 
longer  merited  its  sobriquet"  (p.  199).  The  Rev.  R.  I.  Tacon,  the  present  Rector 
of  Rollesby,  in  reply  to  some  inquiries  which  I made,  says  that  “ there  are  no 
remains  of  the  ditease,  as  Rollesby  is  especially  noted  for  its  good  land  and  fine 
crops."  Then  there  is  the  famous  case,  so  frequently  quoted,  of  the  barberry 
