October  2,  1902. 
JOURNAL  OF  HORTICULTURE  AND  COT I'A  JF.  GARDENER. 
309 
Pollination  in  Orchards. 
It  has  been  frequently  noticed  that  in  large  plantations,  of  one 
particular  variety  of  Apple  or  Pear  the  quantity  of  fruit  produced 
greatly  diminishes  from  the  outside  of  the  plantation  towards  its 
centre,  and  the  explanation  apparently  is  that  foreign  pollen, 
that  is,  pollen,  from  another  variety  of  Apple  or  Pear,  as  the 
case  may  be,  is  necessary  for  the  proper  fertilisation  of  the  ovules, 
in  order  that  fruit  may  be  set  at  all.  It  seems  also  that  incom¬ 
plete  fertilisation  may  also  take  place,  owing  possibly  to  weak¬ 
ness  in  the  pollen  of  the  particular  variety,  resulting  in  the 
formation  of  misshapen  or  malformed  fruit . 
The  fertilisation  of  the  ovules  depends  chiefly  upon  three 
factors : — 
1.  The  occurrence  of  suitable  weather  conditions  at  the  time 
of  the  receptivity  of  the  stigma  and  the  ripening  of  the  pollen. 
2.  In  the  case  of  self-sterile  varieties,  the  presence  of  bees  or 
other  bisects  to  carry  pollen  from  one  flower  to  another,  Muller 
gives  a  list  of  nine  bees  visiting  flowers  of  Apple  (Bombus 
hortorum,  L.  9  being  especially  abundant),  as  well  as  other 
insects  (seven)  visiting  the  flower  for  honey  or  pollen  ;  and  a  list 
of  six  bees  (Apis  mellifica,  L.  9  very  abundant),  as  well  as 
twenty-four  other  insects  visiting  the  flowers  of  Pear  (“Fert.  of 
Flowers,”  pp.  238.  239).  Ho  also  says  that  if  bees  fail  to  visit  the 
flowers,  self-fertilisation  occurs  in  each  case,  but  he  is  presumably 
speaking  of  the  wild  plants,  Pyrus  Malus,  L.,  and  P.  communis, 
L.,  and  not  of  a  garden  variety. 
3.  In  the  case  of  the  self-sterile  varieties,  the  presence  of 
plants  in  the  near  neighbourhood  whose  pollen  will  fertilise  the 
ovules  of  the  self-sterile  variety. 
This  last  factor  is  the  one  most  under  the 
control  of  the  grower,  and  therefore  the  one  upon 
which  definite  knowledge  is  essential,  and  though 
much  has  been  done  in  America  in  finding  out 
which  are  the  self-sterile  varieties,  &c.,  very  few 
definite  experiments  carried  out  on  lines  which 
admit,  of  a  minimum  of  error  in  the  result  appear 
to  have  been  conducted,  or  at  least  recorded,  in 
this  country.  American  results  are  not  altogether 
reliable  here,  owing  (1)  to  the  difference  in  the 
varieties  grown,  and  (2)  the  difference  in  the 
meteorological  conditions. 
In  an  attempt  this  season  to  ascertain  which 
varieties  of  Pears  were  self-sterile,  and  therefore 
not  suitable  for  large  plantings  by  themselves,  I 
tested  the  following  fifteen  varieties: — Bellissime 
d’Hiver,  Beurre  d’Amanlis,  Beurre  Superfin, 
Catillac,  Conference,  Doyenne  du  Comice,  Duron- 
deau,  Easter  Beurre,  Emile  cl’Heyst,  Jargonelle, 
Josephine  de  Malines,  Louise  Bonne  of  Jersey, 
Pitmaston  Duchess,  Williams’  Bon  Chretien, 
Olivier  de  Serres.  Of  these  only  two,  Conference 
and  Durondeau,  set  fruit  under  such  conditions 
that  foreign  pollen  (he.,  pollen  of  some  other  var.; 
was  unable  to  obtain  access  to  the  stigmas — i.e., 
only  those  two  vars.  proved  self-fertile. 
So  far  the  evidence  is  positive;  the  evidence 
with  regard  to  the  other  thirteen  varieties  is  not 
conclusive,  the  weather  prevailing  at  the  time 
possibly  interfering  with  the  setting  of  the  fruit. 
Negative  evidence  can  only  be  accepted  in  such 
cases  after  a  long  series  of  experiments  extending 
over  several  years  with  varying  climatic  condi¬ 
tions.  In  some  cases,  although  the  trees  flowered 
very  well,  and  were  growing  close  to  other 
varieties,  only  one  or  two  fruits  were  set,  showing 
that  weather  conditions  interfered  greatly  with 
the  production  of  fruit. 
Thirteen  varieties  of  Apples  were  experi¬ 
mented  on — Beauty  of  Kent,  Cellini  Pippin,  Cox’s 
Orange,  Claygate  Pearmain,  Gladstone,  Lord 
Derby,  Lady  Sudeley,  Mannington  Pearmain, 
Northern  Greening,  Schoolmaster,  Stirling  Castle, 
Sandringham,  Stunner  Pippin,  and  here  again 
only  two  varieties  set  fruit,  under  conditions  pre¬ 
cluding  the  entrance  of  foreign  pollen — Gladstone 
and  Stirling  Castle.  Of  course,  here  again,  the 
negative  evidence  does  not  conclusively  prove 
that  the  remaining  eleven  varieties  were  self- 
sterile. 
The  weather  prevailing  at  the  time,  high  winds 
and  wet,  prevented  any  cross  pollination  experi¬ 
ments  being  carried  out  with  accuracy;  but  it  is 
worth  noting  that,  although  the  Pear-blossoms 
are,  as  a  rule,  at  least,  proterogynous,  yet  it 
frequently  happens  that  one  or  two  of  the  anthers 
have  shed  their  pollen  before  the  bud  opens;  this 
fact  points  to  the  necessity  for  special  care  in  the 
choice  of  flowers  for  cross  pollination. — F.  J.  C. 
— (R.H.S.  Scientific  Committee). 
Town  Trees. 
( Concluded  from  page  2S2.) 
The  Acer  Tribe. 
Like  the  common  Ash,  the  Mock  Plane,  or  Sycamore  (Acer 
pseudo-Plantanus),  finds  w  ay  as  seeds  into  backyards,  areas,  and 
other  confined  places  in  country,  and  sometimes  the  sunniest 
and  confined  towns,  and  seedlings  spring  up  with  astounding 
vigour.  They  are  cherished  in  the  small  front  or  back  garden 
or  yard,  for  who  does  not  love  the  green  thing  that  has  sought 
refuge  and  appeals  for  protection?  The  seedlings  grow  might 
and  main,  embellish  the  situation,  and  help  purify  the  atmo¬ 
sphere.  Anon  they  afford  shade,  become  part  of  the  very  life 
of  the  occupier  of  the  place.  If  space  forbids,  the  heads  are 
lopped  or  cropped,  always  in  winter  time,  and  they  remain 
quite  satisfactory  for  a  lifetime.  Where  there  be  room  the 
young  trees  mount  up  quickly  to  the  height  of  the  first  floor 
windows,  or  even  eaves  and  ridges  of  two-storied  dwellings, 
when,  and  sometimes  long  before,  they  contract  fly  (Aphis 
aceris),  which  strew  the  ground  beneath  with  honeydew,  and 
the  upper  surface  of  the  leaves  become  coated  therewith;  then 
this  turns  black  by  action  of  fungus,  the  leaves  being  very 
unsightly,  and,  worst  of  all,  they  curl  up,  mature,  and  fall  off 
early,  as  this  season,  in  September.  Black  blotch  fungus 
(Rhytisma  acerinum)  also  affects  the  leaves  seriously  in  some 
seasons,  even  this,  and  they  fall  early  in  consequence.  For 
these  reasons  I  do  not  see  the  merits  of  Sycamore  trees  for 
town  planting.  The  bees  are  fond  of  the  flowers  and  their  hum 
may  be  pleasant  to  town  chrellers;  but  this  is  bad  when  the 
Rose,  sulphurea. 
(See  reference  on  page  308) 
