434  Some  Remarks  on  Grape  Culture.  {A™'sl™T;Sh&rm' 
origin  of  so  many  seemingly  conflicting  opinions  relative  to  the  ex- 
emption of  varieties  of  grape  from  mildew,  owing  to  the  effects  pro- 
duced by  this  disease  being  attributed  to  other  supposed  causes. 
It  is  a  disputed  question  whether  or  not  mildew  will  attack  per- 
fectly healthy  vegetation.  By  many  persons  it  is  held  that  fungoid 
growths  only  appear  on  disorganized  vegetable  or  animal  matters ; 
that,  previous  to  the  appearance  of  the  mildew  on  leaves,  some  dis- 
turbing cause  has  been  at  work  on  the  plant,  and  the  partial  decompo- 
sition which  has  resulted  from  the  unhealthy  state  forms  proper  con- 
ditions for  the  development  of  the  fungus.  From  this  reasoning  it 
follows  that,  previous  to  the  appearance  of  mildew,  there  must  exist  a 
disorganization  of  vegetable  tissue ;  and  before  a  remedy  can  be  sug- 
gested we  must  first  endeavor  to  discover  the  cause  of  the  incipient 
disease  which  allows  the  development  of  the  fungoid  growths. 
The  peronospora  is  never  found  on  grape-leaves  which  are  always 
dry.  The  predisposing  cause  of  this  particular  species  of  fungus  is  an 
excess  of  retained  moisture  on  the  foliage,  either  from  continued  wet 
and  damp  weather,  or  from  heavy  night  dews  succeeded  by  calm  days. 
Grape-vines  trained  on  trellises  protected  by  a  covering  at  top,  so  as 
to  prevent  the  radiation  of  heat  from,  and  the  consequent  deposition 
of  dew  upon,  the  surfaces  of  the  leaves  are  never  troubled  by  this 
fungus. 
It  is  also  a  common  observation  that  grape-vines  growing  through 
and  over  trees  are  never  seriously  injured  by  mildew,  the  protection 
afforded  by  the  leaves  of  the  tree  preventing  it.  Branches  from  the 
same  root,  some  of  which  are  allowed  to  ramble  over  a  tree,  and 
others  trained  upon  an  ordinary  trellis,  will  afford  good  examples  as 
to  the  benefits  of  protection  in  preventing  mildew.  Hence  it  may  be 
inferred  that  a  good  locality  for  vineyards  is  one  where  there  is  ex- 
emption from  late  spring  frosts,  from  late  dews  during  summer  nights, 
and  from  early  frosts  in  autumn ;  and  the  best  results  will  be  found 
where  all  these  conditions  exist,  and  failures  will  follow  in  proportion 
to  their  deficiency.  So  far  as  concerns  entire  freedom  from  the  mil- 
dew under  consideration,  the  conditions  are  found  on  sloping  hillsides 
contiguous  to  well-defined  valleys.  It  has  long  been  observed  that 
in  clear,  still  nights  during  summer,  dews  are  less  frequent  upon  the 
sides  of  hills  than  they  are  in  the  neighboring  valleys. 
The  appearance  of  hoar-frost  in  valleys  during  the  early  winter 
and  spring  seasons  is  produced  by  conditions  of  temperature  similar  to 
