﻿200 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  their 
  size 
  are 
  almost 
  meaningless. 
  When 
  we 
  say 
  that 
  average 
  

   rod-shaped 
  bacteria 
  are 
  about 
  y^cfiro 
  mc 
  ^ 
  (TITO 
  mm 
  -) 
  l 
  n 
  g 
  

   and 
  Trr.ooo 
  mcn 
  (iTlV^ 
  mm 
  O 
  m 
  thickness, 
  we 
  are 
  describing 
  

   dimensions 
  so 
  small 
  that 
  we 
  cannot 
  appreciate 
  them. 
  It 
  must 
  

   also 
  be 
  kept 
  in 
  mind 
  that 
  many 
  kinds 
  of 
  bacteria 
  are 
  smaller 
  

   than 
  the 
  dimensions 
  given 
  above. 
  These 
  figures 
  mean 
  more 
  

   when 
  we 
  calculate 
  the 
  number 
  of 
  average 
  bacteria 
  that 
  might 
  

   be 
  contained 
  in 
  a 
  vessel 
  measuring 
  a 
  cubic 
  inch, 
  or 
  when 
  we 
  

  

  measure 
  the 
  thickness 
  of 
  a 
  finger 
  

   nail 
  and 
  estimate 
  how 
  many 
  bacte- 
  

   ria, 
  piled 
  one 
  upon 
  another, 
  would 
  

   be 
  required 
  to 
  make 
  a 
  column 
  as 
  

   high 
  as 
  the 
  finger 
  nail 
  is 
  thick. 
  

   Such 
  estimates 
  will 
  make 
  it 
  quite 
  

   clear 
  that 
  bacteria 
  are 
  small 
  enough 
  

   to 
  be 
  everywhere 
  and 
  yet 
  escape 
  

   our 
  attention. 
  Bacteria 
  are 
  of 
  three 
  

   different 
  forms. 
  Most 
  of 
  them 
  are 
  

   rod-shaped, 
  or 
  of 
  the 
  bacillus 
  form, 
  

   some 
  are 
  spherical, 
  and 
  still 
  others 
  

   are 
  spiral 
  in 
  form 
  (fig. 
  165). 
  The 
  

   rod 
  bacteria 
  vary 
  in 
  length 
  and 
  in 
  

   diameter. 
  Similarly, 
  spherical 
  bac- 
  

   teria 
  vary 
  in 
  size, 
  and 
  some 
  spiral 
  

   forms 
  may 
  consist 
  of 
  less 
  than 
  one 
  

   complete 
  spiral, 
  others 
  of 
  a 
  dozen 
  or 
  more 
  spirals. 
  

  

  Little 
  is 
  known 
  about 
  the 
  structure 
  of 
  these 
  minute 
  plants. 
  

   The 
  definitely 
  organized 
  cell 
  wall 
  contains 
  a 
  small 
  amount 
  of 
  

   protoplasm, 
  which 
  sometimes 
  forms 
  extruding 
  cilia 
  (fig. 
  165). 
  

   By 
  means 
  of 
  these 
  cilia 
  some 
  kinds 
  of 
  bacteria 
  are 
  able 
  to 
  swim, 
  

   and 
  some 
  of 
  them 
  move 
  with 
  a 
  speed 
  (over 
  two 
  thousand 
  

   times 
  their 
  o\vn 
  length 
  in 
  one 
  hour) 
  which 
  is 
  remarkably 
  

   rapid 
  in 
  proportion 
  to 
  their 
  small 
  size. 
  Definite 
  nuclei 
  have 
  

   not 
  been 
  seen 
  in 
  bacteria, 
  but 
  it 
  may 
  be 
  that 
  certain 
  granular 
  

   fragments 
  represent 
  the 
  nucleus. 
  We 
  are 
  more 
  interested, 
  

   however, 
  in 
  how 
  bacteria 
  live 
  than 
  in 
  their 
  structure. 
  

  

  FIG. 
  105. 
  A 
  group 
  of 
  bacteria 
  

   illustrating 
  type 
  forms 
  

  

  A, 
  spherical 
  bacteria 
  gathered 
  iiito 
  

   a 
  colony, 
  ami 
  />', 
  spherical 
  bacte- 
  

   ria 
  arranged 
  in 
  a 
  chain 
  ; 
  (', 
  J>. 
  K, 
  

   and 
  /', 
  rod. 
  or 
  bacillus, 
  bacteria, 
  

   E 
  and 
  A' 
  having 
  cilia: 
  G 
  and 
  //, 
  

   spiral 
  bacteria, 
  the 
  former 
  less 
  

   than 
  one 
  complete 
  spiral, 
  and 
  the 
  

   latter 
  several 
  spirals. 
  Rearranged 
  

   after 
  Jordan 
  

  

  