﻿G. 
  M. 
  Thomson.— 
  -Om 
  the 
  Fertilization 
  of 
  some 
  New 
  Zealand 
  Orchids. 
  421 
  

  

  margin 
  is 
  the 
  rostellum. 
  Tliis 
  is 
  formed 
  of 
  large 
  cells, 
  covered 
  with 
  a 
  very 
  

   delicate 
  membrane. 
  If 
  this 
  be 
  touched 
  with 
  a 
  bristle, 
  it 
  is 
  almost 
  instantly- 
  

   ruptured, 
  and 
  a 
  small, 
  very 
  viscid 
  drop 
  of 
  matter 
  exudes. 
  In 
  "withdrawing 
  

   the 
  bristle 
  the 
  pollinia 
  are 
  brought 
  away 
  with 
  it. 
  The 
  anther 
  is 
  terminal 
  

   (posterior), 
  and 
  has 
  broad 
  lateral 
  projections. 
  The 
  pollinia 
  are 
  four 
  in 
  

   number, 
  in 
  two 
  pairs, 
  and 
  in 
  the 
  form 
  of 
  plates. 
  The 
  flowers 
  do 
  not 
  appear 
  

   to 
  secrete 
  any 
  nectar, 
  but 
  when 
  the 
  surface 
  of 
  the 
  labellum 
  is 
  slightly 
  

   punctured, 
  a 
  considerable 
  amount 
  of 
  sweetish 
  purple 
  juice 
  exudes, 
  which 
  is 
  

   probably 
  grateful 
  to 
  insects. 
  From 
  the 
  shape 
  of 
  the 
  flowers, 
  it 
  is 
  necessary 
  

   to 
  cut 
  them 
  longitudinally 
  to 
  see 
  the 
  parts. 
  Looking 
  at 
  the 
  position 
  of 
  tho 
  

   anther 
  and 
  stigma, 
  it 
  appears 
  to 
  me 
  almost 
  impossible 
  that 
  self-fertilization 
  

   can 
  take 
  place 
  ; 
  at 
  the 
  same 
  time 
  it 
  is 
  somewhat 
  difficult 
  to 
  suggest 
  any 
  

   satisfactory 
  way 
  in 
  which 
  an 
  insect 
  could 
  accomplish 
  either 
  this 
  or 
  cross- 
  

   fertihzation. 
  I 
  presume 
  that 
  any 
  insect 
  entering 
  the 
  flower 
  would 
  have 
  to 
  

   back 
  out 
  again 
  by 
  the 
  same 
  way 
  as 
  it 
  entered, 
  and 
  in 
  doing 
  so 
  it 
  would 
  

   come 
  in 
  contact 
  with 
  the 
  rostellum, 
  and 
  would 
  remove 
  the 
  pollinia 
  on 
  its 
  

   head. 
  It 
  is 
  also 
  probable 
  that, 
  in 
  endeavouring 
  to 
  obtain 
  from 
  a 
  second 
  

   flower 
  any 
  of 
  the 
  sweet 
  juices 
  from 
  the 
  tissue 
  at 
  the 
  base 
  of 
  the 
  labellum, 
  it 
  

   would 
  slightly 
  advance 
  its 
  head, 
  so 
  as 
  to 
  bring 
  the 
  pollinia 
  attached 
  to 
  it 
  on 
  

   to 
  the 
  stigma. 
  Again, 
  it 
  is 
  possible 
  that 
  self-fertilization 
  might 
  be 
  secured 
  

   by 
  an 
  insect 
  thus 
  getting 
  the 
  pollinia 
  on 
  its 
  head, 
  and 
  then 
  endeavoming 
  to 
  

   push 
  its 
  way 
  down 
  through 
  the 
  small 
  lateral 
  apertures. 
  In 
  doing 
  so, 
  it 
  

   would 
  almost 
  certainly 
  smear 
  the 
  stigma 
  with 
  pollen 
  from 
  the 
  same 
  flower, 
  

   and 
  I 
  have 
  sometimes 
  been 
  inchned 
  to 
  think 
  that 
  such 
  did 
  take 
  place. 
  At 
  

   the 
  same 
  time, 
  this 
  Avould 
  seem 
  like 
  putting 
  an 
  unnecessary 
  difficulty 
  in 
  the 
  

   way 
  of 
  what 
  is 
  usually 
  a 
  vei-y 
  simple 
  process, 
  and 
  therefore 
  no 
  great 
  value 
  

   is 
  to 
  be 
  attached 
  to 
  tliis 
  idea. 
  

  

  For 
  a 
  time 
  I 
  could 
  not 
  understand 
  why 
  spiders 
  frequented 
  these 
  flowers 
  

   so 
  much, 
  but 
  I 
  soon 
  found 
  a 
  sufficient 
  cause. 
  The 
  only 
  insects 
  capable 
  of 
  

   removing 
  pollen 
  which 
  were 
  found 
  about 
  the 
  flowers 
  were 
  small 
  Diptera 
  — 
  

   probably 
  a 
  species 
  of 
  Culex. 
  In 
  several 
  cases 
  these 
  small 
  flies 
  had 
  penetrated 
  

   into 
  the 
  tube 
  of 
  the 
  flower, 
  and, 
  in 
  their 
  eagerness 
  after 
  the 
  sweet 
  juices 
  

   found 
  there, 
  brought 
  their 
  heads 
  in 
  contact 
  with 
  both 
  rostellum 
  and 
  stigma, 
  

   and 
  partly 
  owing 
  to 
  the 
  viscidity 
  of 
  these 
  parts, 
  and 
  partly 
  to 
  the 
  narrowness 
  

   and 
  bending 
  of 
  the 
  tube, 
  were 
  unable 
  to 
  withdraw 
  backwards. 
  In 
  some 
  

   flowers 
  insects 
  were 
  thus 
  found 
  still 
  alive, 
  in 
  others 
  they 
  were 
  dead, 
  while 
  

   in 
  many 
  others 
  only 
  portions 
  of 
  them, 
  such 
  as 
  legs, 
  wings, 
  etc., 
  were 
  left, 
  

   the 
  spiders 
  having 
  devoured 
  the 
  rest. 
  In 
  every 
  case 
  in 
  which 
  a 
  captured 
  

   insect 
  was 
  withdrawn 
  from 
  its 
  trap, 
  the 
  pollinia 
  were 
  removed 
  also, 
  securely 
  

   attached 
  to 
  the 
  front 
  of 
  the 
  head. 
  

  

  I 
  closely 
  examined 
  143 
  flowers, 
  and 
  found 
  that 
  in 
  47 
  the 
  polhnia 
  were 
  

  

  