Report  on  Wheat-Mildew. 
653 
consistency  of  the  soil,  are  as  important  as  the  chemical  constitu- 
tion of  it,  whether  natural  or  artificial.  At  this  point  it  will  be 
desirable  to  inquire  whether  the  popular  opinion  which  I have 
recorded  has  any  scientific  basis.  I am  fortunate  enough  to 
have  communications  from  two  recognised  authorities  to  lay 
before  my  readers,  which,  if  they  are  not  absolutely  in  accord  in 
detail,  are  thoroughly  in  support  of  the  idea  that  the  chemical 
constituents  of  the  soil  have  an  important  effect  in  promoting 
and  encouraging  attacks  of  mildew.  The  first  of  these  is  from 
Sir  J.  B.  Lawes,  Bart.,  who  writes  to  me  as  follows  : — 
“ Kothamsted,  St.  Albans,  Nov.  22,  1882. 
“ Dear  Mr.  Little, 
“ tJpon  reading  over  your  questions  respecting  mildew,  I felt  really  so 
■ashamed  of  myself  for  having  so  little  to  say  upon  the  subject,  that  I kept 
your  circular  before  me,  hoping  that  I might  have  something  to  say  on  the 
subject.  Your  letter,  however,  puts  a question  to  me  upon  which  I have  a 
very  decided  opinion,  although  I am  bound  to  say  that  it  has  reference  to 
diseases  of  all  sorts  which  attack  our  crops,  and  not  in  reference  to  mildew 
alone.  I consider  that  plants  are  liable  to  he  attacked  by  fungi,  parasites, 
insects,  &c.,  in  proportion  as  the  soil  is  deficient  in  available  mineral  food. 
I happened  to  pass  through  the  fen  district  in  the  summer  of  1881,  and  I par- 
ticularly noticed  the  dreadful  state  of  the  wlieat.in  that  district ; and  as  my 
I own  wheat,  although  not  a good  crop,  had  not  suffered  from  mildew,  I was 
anxious  to  know  whether  the  season  in  that  district  possessed  any  special 
•character  differing  from  my  own.  According  to  my  view,  fen-land  wheat 
should  be  specially  liable  to  mildew,  as  the  hr  lance  of  the  soil  constituents  is 
organic  and  not  mineral.  Ordinary  arable  land,  such  as  mine,  contains  about 
97  per  cent,  of  mineral  matter  and  3 per  cent,  of  vegetable  substance  • some  of 
the  fen  land  must  have  these  proportions  almost  reversed.  It  is  quite  possible 
that  when  the  climate  favours  mildew  it  will  prevail  more  or  less,  but  that 
the  extent  to  which  it  will  prevail  will  greatly  depend  upon  the  relation 
between  the  mineral  and  organic  matter  in  the  soil ; and  I should  be  disposed 
to  say  that  the  greater  the  amount  of  available  mineral  matter  (potash,  lime, 
silica,  phosphate)  at  the  disposal  of  the  plant,  the  greater  would  be  its  power  of 
resistance.  I have  taken  out  from  our  wheat  experiments  two  experiments, 
on  one  of  which  only  mineral  manures  were  used,  and  on  the  other  only 
ammonia.  You  will  observe  that  the  crop  receiving  ammonia  is  generally  the 
larger,  which  means  that  the  crop  is  more  capable  of  finding  minerals  in  the 
soil  than  ammonia.  You  will  see,  however,  that  the  weight  of  the  bushel  is 
generally  lower  where  ammonia  is  used,  and  that  the  proportion  of  offal  com 
to  dressed  com,  which  is  a measure  of  disease  of  all  sorts,  is  very  high  in  the 
•ammonia  plots. 
“ Yours  truly, 
“ J.  B.  Lawes.” 
The  table  showing  the  results  of  the  experiments  to  which 
Sir  J.  B.  Lawes  refers  in  the  preceding  letter  is  given  in 
•an  Appendix  to  this  Report.*  It  will  be  sufficient  if  I give  in 
this  place  the  average  results  of  the  thirty-one  years,  and  some 
■of  the  extraordinary  variations  from  this  average. 
* App.  V.,  p.  690. 
