﻿142 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  It 
  is 
  worth 
  while 
  to 
  mention 
  the 
  fact 
  that 
  the 
  characters 
  of 
  

   the 
  cleistogamoiis 
  flowers 
  of 
  some 
  violets 
  are 
  so 
  sharply 
  de- 
  

   fined 
  that 
  they 
  are 
  of 
  much 
  use 
  in 
  enabling 
  the 
  botanist 
  to 
  

   distinguish 
  one 
  species 
  from 
  another. 
  

  

  134. 
  Variety 
  of 
  means 
  for 
  pollination. 
  The 
  details 
  of 
  tl 
  it- 
  

   process 
  by 
  which 
  sonic 
  kinds 
  of 
  pollination 
  are 
  secured 
  are 
  

   most 
  complicated. 
  It 
  has 
  taken 
  the 
  studies 
  of 
  many 
  botanists, 
  

   based 
  often 
  on 
  thousands 
  of 
  observations 
  and 
  carried 
  through 
  

   a 
  lifetime, 
  to 
  work 
  out 
  our 
  present 
  fairly 
  exact 
  knowledge 
  of 
  

  

  most 
  of 
  the 
  methods. 
  lU-iMnm-rs 
  

  

  O 
  

  

  in 
  botany, 
  in 
  a 
  school 
  course, 
  

   can 
  hardly 
  do 
  more 
  than 
  follow 
  

   in 
  a 
  very 
  few 
  instances 
  some 
  of 
  

   the 
  steps 
  of 
  the 
  original 
  inves- 
  

   tigators 
  of 
  the 
  pollination 
  of 
  

  

  FIG. 
  125. 
  Self-pollinated 
  flowers 
  flowers 
  ' 
  Merely 
  reading 
  about 
  

   of 
  knotgrass 
  (Polyyonum 
  avicularc) 
  the 
  processes 
  is 
  not 
  enough; 
  

  

  the 
  flowers 
  must 
  be 
  watched 
  

   out 
  of 
  doors, 
  and 
  then 
  their 
  

   structures 
  carefully 
  examined 
  

   in 
  the 
  laboratory. 
  

  

  In 
  the 
  present 
  chapter 
  only 
  

   about 
  ten 
  floral 
  types 
  will 
  be 
  

  

  briefly 
  discussed, 
  out 
  of 
  nearly 
  thirty 
  under 
  which 
  flowers 
  

   have 
  been 
  classed 
  with 
  reference 
  to 
  their 
  form 
  and 
  mode 
  of 
  

   securing 
  pollination. 
  1 
  

  

  135. 
  Knotgrass 
  2 
  ; 
  self-pollination. 
  The 
  common 
  dooryard 
  

   weed 
  known 
  as 
  knotgrass, 
  kuotweed, 
  or 
  doonveed 
  is 
  one 
  of 
  

   the 
  best 
  examples 
  of 
  a 
  plant 
  with 
  (lowers 
  suited 
  only 
  for 
  self- 
  

   pollination. 
  The 
  flowers 
  (fig. 
  125) 
  are 
  very 
  small 
  (often 
  not 
  

   as 
  large 
  as 
  the 
  head 
  tit' 
  a 
  pin), 
  greenish, 
  and 
  borne 
  singly 
  in 
  

   the 
  axils 
  of 
  the 
  leaves. 
  They 
  are 
  destitute 
  of 
  nectar 
  and 
  with- 
  

   out 
  odor, 
  so 
  they 
  do 
  not 
  attract 
  insects. 
  There 
  are 
  usually 
  

   eight 
  stamens, 
  five 
  outer 
  and 
  three 
  inner 
  ones 
  ; 
  these 
  latter, 
  on 
  

  

  1 
  Sec 
  Knutli-Duvis, 
  Handbook 
  of 
  Flower 
  Pollination, 
  Vol. 
  I. 
  Clarendon 
  

   1'ivss, 
  Oxford. 
  - 
  I'olyyonuin 
  aviculare. 
  

  

  A, 
  top 
  view; 
  B, 
  lengthwise 
  section. 
  

   Five 
  stamens 
  bend 
  outward 
  and 
  the 
  

   other 
  three 
  bend 
  inward 
  until 
  their 
  

   an 
  tilers 
  overhaul; 
  the 
  st 
  ii;mas 
  .<</, 
  thus 
  

   making 
  self-pollination 
  extremely 
  

   easy. 
  Magnified 
  about 
  (> 
  diameters. 
  

   After 
  H. 
  Miiller 
  

  

  