﻿256 
  INTRODUCTION 
  TO 
  BOTANY 
  

  

  a 
  period 
  of 
  dormancy, 
  usually 
  lasting 
  through 
  the 
  whiter, 
  

   these 
  spores 
  germinate. 
  From 
  each 
  cell 
  of 
  the 
  winter 
  spores 
  

   in 
  the 
  spring 
  there 
  grows 
  a 
  small 
  hypha 
  (fig. 
  198, 
  "). 
  Each 
  

   cell 
  of 
  this 
  hypha 
  forms 
  one 
  thin-walled 
  spore 
  (jsporidium). 
  

  

  This 
  rust 
  (Puccinia 
  graminis) 
  has 
  another 
  stage 
  in 
  its 
  life 
  

   cycle. 
  The 
  sporidia, 
  when 
  alighting 
  upon 
  leaves 
  of 
  a 
  shrubby 
  

   plant 
  known 
  as 
  the 
  barberry, 
  grows 
  and 
  produces 
  within 
  the 
  

   leaf 
  an 
  extensive 
  growth 
  of 
  mycelium. 
  When 
  this 
  mycelium 
  

   produces 
  spores, 
  they 
  appear 
  hi 
  a 
  peculiar 
  cup 
  on 
  the 
  under- 
  

   side 
  of 
  the 
  barberry 
  leaf 
  (fig. 
  198, 
  F). 
  These 
  spores, 
  being 
  

   different 
  from 
  any 
  of 
  the 
  three 
  described, 
  and 
  being 
  formed 
  

   in 
  a 
  cup, 
  are 
  called 
  cup 
  spores. 
  Cup 
  spores 
  reproduce 
  the 
  rust 
  

   plant 
  upon 
  wheat 
  and 
  oats. 
  Summer 
  spores 
  persist 
  through 
  

   the 
  winter, 
  and 
  it 
  is 
  thought 
  that 
  they 
  also 
  reproduce 
  the 
  rust 
  

   upon 
  oats 
  and 
  wheat 
  in 
  the 
  following 
  spring. 
  No 
  satisfactory 
  

   preventive 
  for 
  this 
  fungus 
  has 
  been 
  discovered. 
  Some 
  progress 
  

   has 
  been 
  made 
  by 
  learning 
  which 
  varieties 
  of 
  wheat 
  and 
  oats 
  

   are 
  most 
  resistant 
  to 
  attacks 
  by 
  the 
  parasite. 
  1 
  

  

  243. 
  Mushrooms. 
  In 
  this 
  sub-division 
  of 
  stalk 
  fungi 
  those 
  

   members 
  that 
  are 
  good 
  to 
  eat 
  have 
  been 
  popularly 
  called 
  

   mushrooms, 
  while 
  those 
  not 
  edible 
  were 
  called 
  toadstools. 
  

   Scientifically 
  there 
  is 
  no 
  accepted 
  distinction 
  of 
  any 
  kind, 
  and 
  

   the 
  name 
  mushroom 
  is 
  now 
  being 
  used 
  for 
  the 
  whole 
  group. 
  

   In 
  a 
  given 
  genus 
  some 
  species 
  may 
  be 
  edible, 
  others 
  not. 
  

   Also, 
  some 
  species 
  are 
  edible 
  while 
  young, 
  but 
  not 
  so 
  when 
  

   older. 
  Some 
  of 
  the 
  more 
  common 
  edible 
  species 
  are 
  easily 
  

   learned 
  and 
  not 
  readily 
  confused 
  with 
  poisonous 
  forms. 
  In 
  

   the 
  United 
  States 
  over 
  one 
  thousand 
  edible 
  forms 
  are 
  known, 
  

   but 
  some 
  of 
  them 
  are 
  very 
  rare. 
  

  

  244. 
  The 
  general 
  character 
  of 
  mushrooms. 
  The 
  mycelium 
  

   of 
  mushrooms 
  lives 
  entirely 
  within 
  the 
  material 
  which 
  fur- 
  

   nishes 
  its 
  nourishment, 
  and 
  from 
  this 
  mycelium 
  it 
  may 
  send 
  

   up 
  into 
  the 
  air 
  the 
  spore-bearing 
  structure 
  commonly 
  regarded 
  

   as 
  the 
  entire 
  mushroom. 
  The 
  mycelium 
  becomes 
  very 
  exten- 
  

   sive 
  and 
  forms 
  moldy 
  or 
  cobweb-like 
  threads 
  within 
  the 
  rich 
  

  

  i 
  " 
  Rusts 
  of 
  Cereals," 
  Bulletin 
  109, 
  S.Dak. 
  Agr. 
  Exp. 
  Sta., 
  1908. 
  

  

  