﻿THE 
  BACTERIA 
  

  

  211 
  

  

  or 
  to 
  drying, 
  but 
  can 
  endure 
  low 
  temperatures. 
  During 
  the 
  

   winter 
  they 
  live 
  in 
  the 
  diseased 
  twigs. 
  In 
  the 
  early 
  growing 
  

   season 
  the 
  leaves 
  and 
  young 
  growth 
  of 
  the 
  twigs 
  become 
  

   blackened 
  and 
  soon 
  wilt 
  as 
  a 
  result 
  of 
  the 
  internal 
  growth 
  of 
  

   the 
  parasite. 
  The 
  bacteria 
  secure 
  nourishment 
  from 
  the 
  cells 
  

   of 
  the 
  host. 
  They 
  may 
  partially 
  

   or 
  wholly 
  stop 
  the 
  cellular 
  pas- 
  

   sages 
  of 
  the 
  host, 
  and 
  are 
  possibly 
  

   injurious 
  in 
  other 
  ways. 
  

  

  The 
  question 
  of 
  how 
  these 
  bac- 
  

   teria 
  are 
  distributed 
  to 
  new 
  hosts 
  

   is 
  important. 
  Even 
  if 
  they 
  should 
  

   be 
  carried 
  through 
  the 
  air, 
  and 
  

   should 
  withstand 
  the 
  consequent 
  

   drying 
  and 
  sunshine, 
  and 
  should 
  

   fall 
  upon 
  the 
  surface 
  of 
  twigs, 
  

   leaves, 
  or 
  fruit 
  of 
  the 
  proper 
  host, 
  

   it 
  is 
  said 
  that 
  they 
  could 
  not 
  

   make 
  their 
  way 
  into 
  the 
  tissue. 
  

   It 
  is 
  believed 
  that 
  the 
  common 
  

   method 
  of 
  infection 
  is 
  by 
  means 
  

   of 
  biting 
  or 
  stinging 
  insects 
  or 
  of 
  

  

  nectar-hunting 
  insects 
  that 
  visit 
  FlG 
  - 
  17 
  - 
  A 
  crown 
  gall 
  produced 
  

   n 
  -. 
  ,. 
  -i 
  TT1 
  by 
  bacteria 
  (Bacillus 
  tumifaciens) 
  

  

  the 
  flowers 
  and 
  fruit. 
  When 
  a 
  O 
  n 
  young 
  apple 
  tree 
  ' 
  

  

  few 
  bacteria 
  are 
  inserted 
  into 
  a 
  ^ 
  thetissueuftheappleplantwhich 
  

  

  new 
  twig, 
  leaf, 
  or 
  floral 
  Structure, 
  grew 
  around 
  the 
  infected 
  area, 
  thus 
  

  

  the 
  infection 
  may 
  spread 
  several 
  producing 
  the 
  knotted 
  growth 
  known 
  

  

  as 
  the 
  >'all. 
  One 
  third 
  natural 
  size 
  

   inches, 
  and 
  soon 
  the 
  blighting 
  

  

  begins. 
  When 
  one 
  flower 
  is 
  infected, 
  insects 
  may 
  carry 
  the 
  

   bacteria 
  to 
  almost 
  every 
  flower 
  on 
  the 
  tree 
  or 
  on 
  other 
  trees 
  

   in 
  the 
  vicinity. 
  Moreover, 
  when 
  the 
  disease 
  has 
  developed 
  far 
  

   enough 
  for 
  the 
  characteristic 
  gummy 
  exudations 
  to 
  appear, 
  

   insects 
  that 
  bite 
  into 
  them 
  may 
  become 
  loaded 
  with 
  the 
  bac- 
  

   teria 
  and 
  may 
  insert 
  some 
  of 
  them 
  into 
  a 
  new 
  host. 
  In 
  pruning 
  

  

  1 
  From 
  "Field 
  Studies 
  of 
  the 
  Crown 
  Gall 
  and 
  the 
  Hairy 
  t 
  Koot 
  of 
  the 
  Apple 
  

   Tree," 
  Bulletin 
  1S6, 
  Bureau 
  of 
  Plant 
  Industry, 
  U.S. 
  Dept. 
  Agr., 
  1910. 
  

  

  