Report  on  Wheat- Mildew. 
663 
first  observation  of  the  disease,  I have  no  further  information,  and 
I must  conclude  this  paper,  which  has  already  exceeded  its  fair 
limits,  by  a few  general  observations  on  the  results  of  the  inquiry. 
1.  It  would  appear  that  seasons  are  the  chief  cause  of  mildew, 
and  that  sudden  changes  of  temperature  and  rain,  accompanied 
with  close  still  weather,  are  favourable  to  the  spread  of  the  disease. 
2.  That  low-lying  rich  soils  are  most  subject  to  attack. 
3.  That  high  farming  and  too  generous  manuring,  particu- 
larly with  nitrogenous  manures,  promote  mildew. 
4.  That  early  sowing  is  desirable  on  all  lands  subject  to 
mildew. 
5.  That  a thin  and  gathering  crop  runs  more  risk  of  the 
disease  than  an  evenly  planted  crop. 
6.  That  while  no  description  of  wheat  is  proof  against  disease, 
red  wheats  are  generally  less  injured  by  it  than  white  wheats. 
There  are  some  points  on  which  further  inquiry  seems 
desirable,  and  amongst  these  I would  particularly  urge  that 
observations  should  be  made  as  to  the  relative  amount  of 
evaporation  from  soils  of  different  descriptions.  While  I have 
been  most  anxious  to  prove  that  atmospheric  conditions  are  not 
the  sole  governing  cause  of  mildew,  I must  not  be  supposed  to 
deny  for  one  moment  that  a condition  of  humidity  and  saturation 
of  the  air  is  required  to  develop  the  disease.  It  may  be  that 
upon  this  depends  some  of  the  difference  between  soils  which 
are  similarly  situated  and  farmed  in  the  same  manner ; and  that 
a gross  and  luxuriant  growth  may  occur  here  without  inducing 
mildew,  while  there  a similar  crop,  growing  on  land  which 
rapidly  cools  the  lower  stratum  of  air  and  thus  produces  mist,  is 
fatally  injured. 
Again,  I think  that  the  exact  influence  of  particular  chemical 
constituents  on  the  tissues  of  the  plant  is  deserving  further  inquiry. 
I have  already  intimated  in  the  early  part  of  this  paper  that 
perhaps  we  have  yet  more  to  learn  as  to  the  life-history  of 
the  mildew  fungus,  and  I trust  that  our  mycologists  will  pursue 
their  inquiries  with  unabated  ardour. 
Although  I have  not  been  successful  in  elucidating  all  the 
facts  connected  with  this  mysterious  and  baneful  disease,  I trust 
that  I may  have  been  able  to  collect  some  information  which  may 
be  useful  to  other  inquirers. 
I have,  in  conclusion,  to  offer  my  very  sincere  thanks  to  all 
those  who  have  assisted  me,  including  the  correspondents  who 
favoured  me  with  replies  to  my  inquiries.  My  thanks  are 
specially  due  to  Mr.  H.  M.  Jenkins,  the  Secretary  of  the 
Society  ; to  Mr.  Plowright,  to  whom  I owe  most  of  what  I know 
of  the  mildew  fungus  ; and  also  to  Dr.  Voelcker  and  Sir  John 
Lawes  for  their  contributions. 
