﻿GLOSSARY 
  351 
  

  

  Involucre 
  (rolled 
  within). 
  The 
  leaf-like 
  or 
  bract-like 
  sheath 
  that 
  in- 
  

   closes 
  a 
  cluster 
  of 
  flowers. 
  

  

  ' 
  Irritability. 
  The 
  capacity 
  which 
  protoplasm 
  possesses 
  of 
  respond- 
  

   ing 
  to 
  stimuli, 
  such 
  as 
  light, 
  heat, 
  gravity, 
  and 
  contact 
  with 
  chemical 
  

   reagents. 
  

  

  Isogamous 
  (equal 
  gametes). 
  Applied 
  to 
  those 
  plants 
  whose 
  pairing 
  

   gametes 
  are 
  similar. 
  

  

  Lamina 
  (a 
  layer). 
  The 
  blade 
  or 
  expanded 
  part 
  of 
  a 
  leaf. 
  

  

  Leaf 
  trace. 
  The 
  fibrovascular 
  bundles 
  from 
  the 
  leaf 
  which 
  blend 
  with- 
  

   in 
  the 
  stem 
  with 
  its 
  fibrovascular 
  cylinder. 
  

  

  Lenticel. 
  A 
  round, 
  oval, 
  or 
  lens-shaped 
  opening 
  on 
  the 
  exterior 
  surface 
  

   of 
  the 
  bark. 
  

  

  Leucoplast 
  (white 
  molded). 
  A 
  minute 
  colorless 
  body 
  within 
  a 
  cell. 
  

   When 
  exposed 
  to 
  light, 
  leucoplasts 
  may 
  develop 
  into 
  chloroplasts. 
  

  

  Liana. 
  A 
  climbing 
  plant. 
  

  

  Ligule 
  (a 
  small 
  tongue). 
  In 
  grasses 
  a 
  thin 
  appendage 
  at 
  the 
  junction 
  

   of 
  leaf 
  blade 
  and 
  sheath. 
  

  

  Medullary. 
  Relating 
  to 
  the 
  pith 
  ; 
  medullary 
  rays 
  are 
  the 
  pith 
  rays 
  

   which 
  radiate 
  to 
  the 
  bark 
  between 
  the 
  fibrovascular 
  bundles. 
  

  

  Megasporangium 
  (large 
  spore 
  vessel). 
  The 
  sporangium 
  that 
  produces 
  

   the 
  megaspores. 
  

  

  Megaspore 
  (great 
  or 
  large 
  spore). 
  The 
  larger 
  one 
  of 
  the 
  two 
  kinds 
  of 
  

   asexual 
  spores 
  produced 
  by 
  certain 
  pteridophytes 
  and 
  all 
  spermatophytes. 
  

  

  Megasporophyll 
  (large 
  spore 
  leaf). 
  The 
  leaf 
  upon 
  which 
  the 
  mega- 
  

   sporangium 
  develops. 
  

  

  Meristem 
  (dividing 
  tissue). 
  Tissues 
  with 
  the 
  cells 
  all 
  nearly 
  alike 
  

   and 
  still 
  capable 
  of 
  subdividing. 
  

  

  Mesophyll 
  (middle 
  leaf). 
  The 
  green 
  or 
  soft 
  tissue 
  of 
  the 
  inner 
  part 
  

   of 
  the 
  leaf. 
  

  

  Mesophytes 
  (middle 
  plants). 
  Normal 
  land 
  plants 
  such 
  as 
  grow 
  in 
  an 
  

   average 
  soil 
  and 
  under 
  a 
  moderate 
  climate. 
  

  

  Metabolism. 
  Chemical 
  transformations 
  of 
  matter 
  carried 
  on 
  by 
  plants 
  

   in 
  the 
  production 
  and 
  utilization 
  of 
  their 
  food 
  supply, 
  and 
  disposition 
  

   of 
  waste 
  products. 
  

  

  Micropyle 
  (small 
  gate). 
  The 
  opening 
  left 
  by 
  the 
  integuments 
  of 
  the 
  

   ovule, 
  and 
  which 
  leads 
  to 
  the 
  nucellus. 
  

  

  Microsporangium 
  (small 
  spore 
  vessel). 
  The 
  sporangium 
  that 
  produces 
  

   the 
  microspore. 
  

  

  Microspore 
  (small 
  spore). 
  The 
  smaller 
  spore 
  of 
  the 
  two 
  kinds 
  pro- 
  

   duced 
  by 
  certain 
  pteridophytes 
  and 
  all 
  spermatophytes. 
  

  

  Microsporophyll 
  (small 
  spore 
  leaf). 
  The 
  leaf 
  upon 
  which 
  the 
  micro- 
  

   sporangium 
  is 
  borne. 
  

  

  Midrib. 
  The 
  central 
  or 
  main 
  rib 
  of 
  a 
  leaf 
  or 
  thallus. 
  

  

  