August  13,  1903. 
JOUBlsAL  OF  HORTICULTURE  AED  COTTAGE  GARDEEER. 
157 
Spot  on  Sweet  Pea  Plants. 
Eecently  specimens  of  diseased  Sweet  Pea  plants  reached  me 
through  the  Editor  of  the  Journal  of  IJorticuliure,  tlie  plants 
l.eing  a  complete  failure,  some  of  the  seeds  rotting  in  the  ground, 
others  of  the  young  plants  collapsing  when  only  a  few  inches 
high,  one  shown  in  the  figure  at  A,  and  others  again  flowering 
very  indifferently,  the  foliage  withering  (part  of  such  plant 
shown  at  C),  and  the  flowers  puny  and  spotted  in  the  petals. 
On  investigation  the  plants  ^Yere  found  quite  healthy  at  the 
roots,  there  not  being  any  evidence  of  eelvvorm,  and  there  were 
few  nitrogenic  nodosities  (c),  only  a  little  cankerous  affection  on 
the  root-stem  of  the  plant  A  at  d,  and  this  not  sufficient  to 
account  for  the  leafless  condition  of  the  young  plant.  The 
leaflet  {g)  had  several  pale 
spots,  much  more  so  than 
the  rest  of  the  sere  and 
dry  tissue,  and  there  were 
a  few  pallid  and  dry  spots 
on  the  stem  (/),  otherwdse 
not  any  traces  of  disease, 
no  “fruits”  being  dis¬ 
coverable  in  the  tissues  of 
the  leaf  spots,  or  iu  those 
of  the  stem,  though  a  few 
very  minute  dark  dots 
were  observable  iu  a  spot 
on  the  stem  when  ex¬ 
amined  by  a  pocket  lens, 
shown  in  B  at  h. 
The  older  plants,  a 
portion  of  one  at  flowering 
age  shown  iu  C,  had  the 
leaves  very  sickly  looking, 
and  with  many  pale  spots 
{ml)  on  the  whole,  from 
the  base  upward.  An 
affected  leaf  from  the 
flowering  part  of  the  plant 
is  shown  at  D,  the  spots 
being  very  pale,  almost 
white,  and  the  leaf  tissue 
yellowish  and  ,  sickly  - 
looking.  The  spots  ap¬ 
pear  on  green,  healthy 
leaflet  {E  t),  and  the  re¬ 
mainder  of  the  leaflet  (;/) 
soou  assumes  a  yellowish 
hue,  quickly  becomes  sere 
and  withering,  and  not 
any  “fruits”  of  the  fun¬ 
gus  were  discernible  iu 
the  diseased  spots,  these 
drying  up  and  falling  out. 
On  the  older  leaves  that 
had  retained  a  certain 
amount  of  freshness, 
some  of  the  spots  con¬ 
tained  minute  blackish 
specks,  shown  in  F  at  v, 
and  a  section  examined 
under  a  low  power  of  the 
microscope  showed  these 
to  be  perithecia,  or  cou- 
ceptacles  of  the  fungus, 
two  immature  and  em¬ 
bedded  iu  the  diseased 
leaf  tissue,  G  at  ir,  and 
one  mature  perithecium 
(x)  discharging  spores. 
The  spores  are  shown  at 
H,  and  are  referable  to 
Sweet  Pea  plants  affected  \vith  Pea  spot,  Ascochyta  pisi. 
A,  tliseaseil  young  plant,  two-thirds  natural  size  ;  a,  radicle  or  tap-root  STund  ;  b,  side 
roots  and  tibrelets  clean  ;  c,  nitrogenic  nodosities  ;  d,  small  cankerous  spe;  ks  on  root-stem  ; 
e,  collar  of  plant  or  ground  level ;  /,  pale  (disease)  spots  on  stem  ;  g,  only  leaflet  on  plant, 
quite  sere,  and  with  tissue  dropped  out  of  disease  spots. 
B,  portion  of  stem  of  plant  A,  enlarged  two  diameters  :  h,  diseased  spot  that  has  partly 
girdled  stem  ;  i,  sound  tissue. 
C,  root  and  portion  of  top  of  a  plant  arrived  at  flowering  stage,  two-thirds  natural  size  : 
j,  roots  quite  clean  ;  .t,  nitrogenic  nedosities  ;  I,  root-stem  soun  i  ;  in,  stem  above  ground  not 
spotted;  tal,  leaves  diseased  (with  spots  as  shown). 
D,  leaf  from  upper  p.art  of  plant,  two-thirds  natural  size  :  n,  stipules  o,  petiole  ;  j>, 
leaflets  ;  q,  tendril ;  r,  disease  spots  ;  s,  pale  yellowish  green  leaf  tissue. 
E,  leaflet  in  early  but  decisive  stage  of  disease,  natural  size  :  t,  pale  spots  ;  »,  apparently 
sound  but  sickly-looking  portion  of  leaflet,  the  whole  ultimately  withering 
F,  small  leaflet  from  lower  part  of  plant  C  seen  from  under  side,  nacur.  1  size  :  v,  disease 
spots  slightly  raised  at  circumfeience,  and  showing  minute  dark  dots  in  tissue— the  fruits 
(perithecia)  of  fungus. 
(i,  section  through  portion  of  a  diseased  spot,  F,  v:  w,  immature  conceptacles  or  peri¬ 
thecia  of  fungus ;  x,  mature  perithecium  discharging  spores,  X  60. 
H,  conidia  (spores)  of  fungus,  Ascochyta  pisi,  x  200. 
Pea  spot  (Ascochyta  pisi). 
According  to  Massee’s 
“Text  Book  of  Plant  Diseases,”  Pea  spot  is  “sometimes 
injurious  to  cultivated  Peas  (Pisum  sativum),  Haricot  Beans 
(Phaseolus  vulgaris),  and  species  of  Vicia  and  Cercis.”  It  is 
also  sometimes  very  prevalent  on  Everlasting  Peas  (Lathyrus 
sylvestris  platyphyllus,  syn.  L.  latifolius),  completely  withering 
up  large  portions  of  the  leaves  ;  but  in  these  there  seldom  are  any 
“  fruits,”  and  the  same  occurs  in  the  bolder  and  fulsome  leafage 
of  Sweet  Peas  (L.  odoratus).  But  though  not  uncommon  on  the 
leaves  and  stems,  and  even  pods,  the  disease  is  seldom  so 
disastrous  as  to  ruin  the  plants,  as  appears  in  this  instance ;  but 
there  is  no  accounting  for  diseases  passing  from  relatively  passive 
to  a  malignant  epidemic. 
The  sender  of  the  specimens  had  the  same  occur  last  year, 
and  on  newly  broken  up  ground,  so  that  there  could  not  any¬ 
thing  be  attributed  to  disease  from  a  prior  crop.  But  the  sward 
may  have  contained  plants  of  Vicia,  particularly  of  the  Meadow 
Vetchliug  (Lathyrus  pratensis),  and  the  spores  of  the  fungus 
present  that  infected  the  Sweet  Pea  plants.  On  the  other  hand, 
the  burying  down  of  the  sward  wonld  be  calculated  to  render 
infection  less  liable,  and  though  some  seed  rotted  in  the  ground, 
there  is  no  evidence  that  the  disease  is  carried  over  in  the  seed ; 
yet  as  the  fungus  attacks  the  pods,  it  is  not  unlikely  that  seeds 
of  the  stunted  and  deformed  examples  may  also  be  affected.  It 
is  possible  for  the  disease  plasma  to  pass  over  in  the  seed,  and 
the  disease  to  break  out 
iu  spots  on  the  leaves  of 
the  young  plant,®.  But 
on  this  point  we  have  no 
data,  or  even  on  that  of 
the  disease  being  com¬ 
municated  to  cultivated 
plants  from  diseased  wild- 
ling  Lathyrus  or  Vicia, 
though  this  is  the  most 
probable  source  of  in¬ 
fection.  Even  what  the 
resting  stage  of  the  fun¬ 
gus  is  has  not  been  satis¬ 
factorily  determined,  its 
present  form  being  pro¬ 
bably  a  stage  of  a  higher. 
It  produces  small  pale 
spots  on  the  leaves,  stems, 
and  pods,  which  become 
dry  and  brittle,  and  iu  the 
case  of  leaves  eventually 
dropping  out,  giving  to 
the  leaf  the  appearance 
of  having  been  riddled 
with  small  shot,  and 
tiny  perithecia  are  formed 
on  the  diseased  portions. 
The  effect  is  to  greatly 
weaken,  and  in  bad  cases 
cause  the  ruiu  of  the 
plants.  That  is  about  all 
that  is  at  present  known 
of  Ascochyta  pisi. 
In  the  matter  of  pre¬ 
vention,  not  any  means 
are  recorded.  It  is  likely 
that  spraying  with  potas¬ 
sium  sulphide  solution, 
loz  to  gallons  of  water, 
would  hs  useful,  the  sul¬ 
phide  being  first  dissolved 
in  about  a  quart  of  hot 
water,  and  when  dissolved 
adding  2j  gallons  of  soft 
water,  iu  which  loz  of 
softsoap  has  been  mean¬ 
while  dissolved.  Well 
stirred,  the  solution,  being 
cool  enough,  is  ready  for 
use.  Spraying  should 
commence  as  soon  as  the 
plants  are  well  above  the 
ground,  repeating  at  inter¬ 
vals  of  ten  days  or  a 
fortnight,  so  as  to  coat 
the  foliage  as  made  with 
the  finest  possible  film  of 
the  solution,  continuing 
up  to  the  flowering  stage. 
Diseased  portions  should  be  burned,  even  the  haulm  of  old 
plants,  as  it  is  likely  the  resting  stage  is  in  the  dead  plants,  and 
the  spores  discharged  from  perithecia  that  form  iu  the  diseased 
portions,  and  in  the  spring  and  early  summer  infect  any  suitable 
hosts  they  may  alight  upon. 
As  the  ground  was  new  iu  the  particular  instance  referred  to, 
it  is  likely  that  a  dressing  of  lime  would  have  been  useful,  or, 
perhaps  better,  a  dressing  of  basic  cinder  phosphate,  141b  per 
rod,  along  with  dglb  per  rod  of  kainit,  dug  in  and  left  until  near 
