Observations  on  Parasitic  Fungi.  449 
seldom  fails  to  destroy  the  foliage  and  stems,  and  more  or  less  of 
the  tubers. 
If  these  also  are  examined  carefully  under  a strong  lens,  as 
soon  as  they  are  dug  up,  even  healthy  looking  potatoes  will  be 
found  supporting  scattered  plants  and  tufts  of  Botrytis,  as  I have 
frequently  proved  by  finding  them  myself  in  the  above  manner, 
and  afterwards  submitting  them  to  a higher  power  of  the  micro- 
scope ; and  wherever  this  fungus  grows  a blotch  always  succeeds 
it.  Manv  small  white  spots  may  be  seen  on  new  potatoes  at  this 
time,  partially  diseased.  These  spots  consist  of  the  plants  of 
Botrvtis  which  have  fructified  and  fallen  into  a heap,  closely 
adhering  together  by  their  glutinous  surfaces.  If  these  little 
tufts  are  moistened,  innumerable  spores  will  burst  forth  cor- 
responding with  those  of  the  Botrvtis,  and  often  mixed  with 
others,  which  seem  to  follow  closely  in  its  wake,  both  in  the 
ground  and  after  the  crop  is  stored. 
Of  these,  Verticillium  and  Dactvlium  are  conspicuous  ; and 
Botrytis  lateritia  succeeds  them.  The  fact  that  the  Botrytis 
infestans  will  live  and  fructify  on  the  tuber  underground  is  an- 
other important  link  in  the  chain  of  evidence  on  which  this 
question  depends,  and  some  idea  of  its  penetrating  powers  mav 
be  formed  from  the  following  fact.  On  one  occasion,  when  my 
potatoes  were  being  dug,  I noticed  a greyish  appearance  on  a 
portion  of  earth  closely  pressed  into  one  of  the  eyes  of  a potato, 
and  on  submitting  it  to  my  microscope,  I found  it  to  be  the 
Botrvtis  infestans,  which  had  passed  from  the  tuber  nearly  a quar- 
ter of  an  inch  through  the  earth,  and  was  fructifying  on  its  sur- 
face. 
I am  of  opinion  that  the  roots  or  mycelium  of  this  and  similar 
parasites  permeate  the  tissues  of  the  potato  and  other  plants  to 
a considerable  extent,  without  being  able,  under  certain  condi- 
tions of  the  plants,  to  protrude  through  their  skins.  In  one  or 
two  instances  I have  had  ocular  demonstration  that  such  is  the 
fact. 
Having  thus  shown  that  the  Botrytis  infestans  is  the  imme- 
diate instrument  whereby  the  potato  is  destroyed,  I will  endea- 
vour to  trace  the  condition  of  the  plant  from  the  earliest  period 
up  to  the  time  of  its  attack  by  that  fungus. 
I commence  with  an  examination  of  the  young  shoots  pre» 
viouslv  to  planting  the  sets  ; for  in  most  cases  they  sprout  in 
the  places  where  they  are  stored ; and  I can  state  most  positively 
that  these  are  nearly  all  in  a diseased  state,  being  blotched  in 
the  same  manner  as  the  roots  are  found  to  be  after  they  are 
planted.  Accompanying  these  blotches  I find  a small  white 
mildew  composed  of  slender  moniliform  branched  threads  situate 
between  the  healthy  and  diseased  portions.  On  placing  thin 
