Diseases  of  Potatoes. 
265 
rough  and  rugged  appearance,  of  little  value  in  the  market. 
Scabby  potatoes  should  not  under  any  circumstances  be  used 
for  “seed,”  as  the  disease  is  sure  to  reappear  in  the  new  crop. 
The  land  where  these  potatoes  have  been  grown  should  be 
liberally  dressed  with  gas  lime  to  kill  the  organisms  in  the 
soil,  and  the  cultivation  of  potatoes  should  be  discontinued  for 
some  time. 
Potato  canker,  described  in  detail  and  figured  in  the  Report 
for  1902,  has  appeared  again  this  year  and  continues  under 
observation.  I may  add  that  this  year  I found  the  fungus 
attacking  the  roots  of  the  plants  themselves  and  forming  the 
same  cankerous  gi’owth  as  on  the  tuber.  I would  not  advise 
the  use  for  seed  of  any  of  the  diseased  tubers.  Mr.  Worthington 
G.  Smith  has  written  a note  in  the  Gardeners'  Chronicle  of 
October  19, 1904,  to  the  effect  that  he  had  cut  a potato,  affected 
by  this  canker,  in  two,  and  planted  the  pieces  in  an  isolated 
position,  with  the  result  that  two  perfectly  healthy  plants 
appeai’ed,  and  the  crop  was  a heavy  one,  every  tuber  being 
perfectly  sound.  Happily  potato  canker  is  not  yet  often  met 
with,  and  it  may  be  exterminated  or  kept  down  considerably 
by  not  leaving  any  diseased  tubers  on  the  field,  but  removing 
or  burying  them,  and  growing  for  some  time  crops  which 
would  not  be  attacked  by  this  disease. 
Fruit  trees.— 1\\  the  early  part  of  the  year  cases  of  canker 
on  cherry  and  apple  trees  were  sent,  and  the  sender  informed 
as  to  the  best  methods  to  prevent  a spread  of  the  injury.  The 
canker  of  fruit  trees  is  caused  by  a fungus  {Nectria  ditissima), 
which  is,  however,  considered  a wound  parasite,  that  is,  a fungus 
that  attacks  only  tissues  previously  damaged.  These  wounds 
may  be  due  to  frost,  wet,  abrasion  l)y  animals,  bad  pruning,  &c. 
When  a wound  is  observed  it  should  at  once  be  painted  with 
tar,  to  prevent  the  spreading  of  the  infection.  Old  wounds  on 
diseased  trees  should  be  cut  out  with  a sharp  knife,  leaving 
only  healthy  tissue,  and  then  painted  in  the  same  manner. 
Three  cases  of  an  attack  of  the  fungus.  Monilia  fructigena 
Pers.^  have  been  reported  from  different  localities.  This 
fungus  causes  serious  injury  in  orchards  through  its  vei’y 
Explanation  of  Fig.  2. — Warts  on  Potato  (see  pages  261  and  264). 
A,  Half  of  a potato,  showing  the  size  and  distribution  of  the  warts,  b, 
Quarter  of  a potato  with  the  skin  pared  off,  showing  the  dark-brown  patches 
produced  by  the  fungus.  C,  Another  portion  with  the  skin  pared  off,  showing 
the  patches  confluent,  d,  Section  through  a portion  of  a potato,  showing  the 
warts  penetrating  the  substance  of  the  potato  and  raising  up  the  surface  of 
the  skin,  e.  Magnified  section  through  a wart ; — 1 . The  cells  killed  by  the 
fungus  being  pushed  through  the  epidermis.  2.  The  epidermal  layer.  3.  The 
empty  compressed  cells  full  of  the  mycelium  of  the  fungus.  4.  The  uninjured 
cells  of  the  potato  containing  starch  grains. 
> Journal  R.A.S.E.,  Vol.  63,  1902,  pp.  289,  290. 
