270  Annual  Report  for  190J;  of  the  Consultnaj  Botanist. 
APPENDIX. 
Notes  on  a Disease  of  Cncumbers.  I.  By  Professor  P.  Maze, 
Pasteur  Institute,  Pai’is  ; II.  By  Hans  Th.  Gtissow. 
I. 
I received  in  the  middle  of  Novendjer  last  a few  cucumber 
leaves  from  Hayes,  in  Middlesex.  These  leaves,  sent  by  Mr. 
Bethell,  showed  many  brown  irregular  spots  of  various  sizes. 
Leaves  so  affected  perish  rapidly.  Mr.  Bethell  says  that  the 
disease  causes  annually  a loss  of  several  thousand  pounds  to  the 
grower. 
The  damage  is  brought  about  by  a parasitic  fungus  whose 
ramified  anil  septate  mycelium  spreads  in  the  parenchyma  or 
on  the  outside  of  the  leaf.  The  mycelial  filaments,  of  a greenish 
])rown  colour,  give  out  many  conidiophores  which  stand 
ei’ect  in  the  open  air  and  bear  each  a row  of  conidia.  The 
latter  have  the  form  of  an  inverted  club  and  are  divided  into 
several  compartments  by  transverse  partitions.  The  difference 
in  diameter  l)etween  the  two  extremities  of  the  conidium  is 
small,  so  that  the  club  shape  is  not  very  pronounced. 
The  number  of  transverse  partitions  is  variable,  from  one 
to  twelve  or  fifteen.  The  outer  surface  of  the  conidium  is 
smooth  and  plain,  and  presents  no  constrictions  corresponding 
to  the  insertion  of  the  partitions  ; on  the  contrary  the  inner 
surface  shows  some  thickening  where  the  partitions  are 
inserted.  I have  never  seen  longitudinal  partitions,  so  that 
the  spores  present  always  one  series  of  compartments  or  cells. 
This  fungus  thus  appears  to  be  a species  of  Pol pdesmus 
like  the  fungus  observed  by  Frank  in  a disease  of  pumpkhis  in 
the  neighbourhood  of  Berlin. 
Cultivated  in  a pure  condition  on  agar-agar  at  the  tem- 
perature of  the  laboratory,  it  gives  abundant  growth  and 
develops  very  rapidly.  At  first  the  mycelium  is  colourless, 
but  soon  it  becomes  of  a greenish  brown  tinge.  The  colouring 
is  visible  after  twenty-four  hours,  and  from  this  moment  the 
mycelium  forms  spores  similar  to  those  which  are  observed  in 
the  spots  on  the  leaves. 
When  the  culture  has  attained  its  full  development  it 
presents  a thick  velvety  carpet,  forming  one  body  with  the 
substratum.  Its  colour  is  of  a very  dark  brown  with  a slightly 
greenish  tinge.  There  is  a vast  abundance  of  spores  covering 
the  whole  surface  of  the  mycelium,  thus  giving  it  the  above 
noted  velvety  appearance. 
Young  spores,  taken  from  such  a culture  and  placed  in  a 
fresh  agar  tube,  sprout  in  six  hours  at  the  ordinary  tem- 
perature of  20”-22"  C.  (68‘’-72"  F.).  The  germinative  tubes 
start  from  the  two  end  cells  of  the  spore  ; the  intermediary 
