804 
Supplement  to  the  “ Tropical  AgricuUuriM” 
[May  1,  189G. 
and  lower  surfaces  are  seen  to  be  covered  by  a layer 
of  flattened,  or  brick-shaped  cells,  which  contain 
little  more  than  water,  with  the  exception  of  cer- 
tain ones  to  be  described  later.  Between  these 
two  layers  which  constitute  the  upper  and  lower 
epidermis,  is  a mass  of  tissue  in  which  tlie  green 
colour  of  the  leaf  is  formed,  and  running  througli 
this  in  ali  directions  is  a network  of  veins  which 
are  made  of  vascular  ti.ssne  continuous  with  the 
vessels  of  the  stem.  Tlie  cells  in  which  the  green 
colour  is  formed  differ  in  arrangement  towards 
the  two  surfaces  of  the  leaf.  Those  towards  the 
upper  one  are  arranged  close  togetlier  with  very 
few  spaces  between  them  ; tliey  are  oblong  cells 
with  their  long  axes  ])laced  at  right  angles  to  the 
surface.  The  cells  towards  the  lower  surface  are 
not  at  all  regular  in  their  arrangement,  but  are 
very  loo.sely  placed,  .so  that  very  large  intercellul  ir 
spaces  are  found  there.  Tnese  intercelluhir  spaces 
are  continnous  with  each  other,  and  with  others 
that  extend  through  the  leaf  stalk,  stem  and 
root.  The  cells  of  the  leaf  ti.ssue  that  al)ut  upon 
these  spaces  have  very  thin  walls,  and  thus  allow 
readily  of  the  absorption  of  the  gases  found  in  the 
interior  of  the  passages  by  the  cells  bordering  upon 
them.  They  at  the  same  time  allow  a ready  eva- 
poration of  water  from  the  cells  of  the  tissue.  At 
many  points  in  the  leaf  an  intercellular  space  of 
large  size  can  be  seen  to  extend  quite  up  to  the 
epidermis,  and  close  in.«pection  show.s  that  two 
of  the  cells  of  the  latter  layer  have  a small 
slit  between  tliem  which  allows  of  communication 
between  the  external  air  and  the  contents  of  the 
intercellular  space  system.  The  two  cells  tliat  lie 
upon  either  side  of  the  slit  can  have  their  sliapes 
altered  by  variations  in  the  quantity  of  the  water 
they  contain,  and  this  causes  tlie  slits  at  one  time 
to  open  and  at  others  to  be  nearly  or  quite  closed. 
These  openings  are  called  stoynata,  and  the  two 
cells  bounding  them  are  called  r/uard  cells.  In  a 
surface  view  they  are  seen  to  be  somewhat  kidney- 
shaped ; being  attached  to  each  other  only  by  their 
ends;  it  is  evident  that  when  filled  with  water, 
and  consequently  swollen  or  turgid,  they  ojien  the 
slit  by  separating  from  each  other  along  the  greater 
part  of  their  irner  surfaces.  When  on  the  other 
hand  they  have  lost  their  water,  the  strain  on  them 
is  relaxed,  they'  fall  together  and  partially'  or 
wholly  close  the  aperture. 
It  is  however  in  the  cells  of  the  middle  of  the 
leaf  that  the  chemical  work  goes  on.  If  one  of 
these  is  examined  by'  the  high  jmwer  of  a micros- 
cope, it  IS  found  that  the  green  colour  is  not  diffus- 
ed, through  the  substance  of  the  cell,  but  is  con- 
fined to  certain  small  bodies  which  are  embedded 
in  the  layer  of  protoplasm  or  living  substance 
which  lines  the  cell.  These  small  bodies  are  called 
chloroplastids  or  chlorophyll  corpuscles,  and  it  is 
to  them  that  we  must  look  for  the  actual  construc- 
tive activity.  They  are  eventually  small  masses 
of  protoplasm  which  have  loose  or  spongy  arrange- 
ment of  particles,  so  that  there  is  in  each  a com- 
plicated mesh  work.  In  the  meshes  of  this  spongy 
mass  the  green  colour,  known  as  chlorophyll,  lies 
in  the  form  of  a solution.  The  work  done  by  the 
chloroplastid  is  very  comple.v,  but  we  are  able  to 
distinguish  to  a great  extent  between  the  part 
played  by  the  colouring  matter  itself  and  that 
which  is  discharged  by  its  protoplasmic  frame- 
work. 
We  have  in  this  mechanism,  then,  a ready  means 
of  access  of  air  to  the  interior  ti.ssue  of  the  leaf, 
It  enters  at  the  stomata,  and  of  course  fills  all  the 
intercellular  spaces.  The  composition  of  the 
gases  in  the.se  channels  is  not,  however,  the  same 
as  that  of  the  atmosphere,  as  different  giseous 
interchanges  between  the  cells  of  the  leaf,  and 
the  spaces  outside  them  are  continually  taking 
place.  Nevertheless,  whatever  may  be  its  exact 
composition,  we  know  that  it  contains  a small 
quantity  of  carbon  dioxide,  partly  perhaps  derived 
from  the  leaf  itself,  partly  supplied  by  the  small 
amount  always  j)resent  in  atmospheric  air.  By 
virtue  of  its  solubility  in  water  it  easily  penetrates 
the  delicate  cells  of  the  tissue,  the  walls  of  which 
are  saturated  with  water,  and  so  it  comes  into 
contact  with  the  ch.loroplastid.s. 
Not  only  is  air  thus  admitted.  We  find  that 
water  taken  in  from  the  soil  by  the  roots,  contain- 
ing various  mineral  and  other  constituents  in  so- 
lution, also  easily'  reaches  the  leaf.  No  part  of 
tlie  constructing  tissue  is  situated  very  far  from  a 
vein,  and  the  woody'  portion  of  sucli  vein  being 
in  direct  connexion  with  the  woody  tissue  of  the 
stem,  a path  of  ascent  and  distribution  is  readily 
afforded. 
Thus  the  raw  materials,  w'hich  w’e  know  by' 
experiment  that  the  plant  absorbs,  meet  each  other 
in  the  cells  of  the  leaf,  finding  themselves  there 
in  the  presence  of  the  living  substance  of  the 
cell,  and  of  certain  differentiated  bodie.'^,  the 
chloroplastids.  These  are  the  first  conditions  for 
constructive  activity'. 
SORGHUM  IlALAPENSIi:. 
This  indigenous  grass  (identical  with  Andropogon 
halapensis)  is  referred  to  by  Mr.  Wm.  Ferguson  in 
his  notes  on  the  grasses  growing  in  Ceylon,  as  being 
abundant  on  the  banks  of  the  Haragam-oya, 
about  eight  miles  from  Kandy'.  He  states  that  some 
roots  grown  in  his  garden  in  Colombo  W'ere  from 
eight  to  ten  feet  high.  “ I have  not,”  he  remarks, 
“ tried  it  as  a fooder  grass,  but  should  imagine 
that  it  is  quite  equal  to  the  Euchloena  (Reana) 
luxurians,  Androscepia  gigantea,  or  any  of  the 
gigantic  grasses  introduced  to  the  Island  and  so 
highly  recommended  as  fodder  plants.”  It  is  said 
to  be  indigenous  to  Southern  Europe,  Syria,  Cuba, 
and  Northern  Africa,  and  cultivated  in  the  Brazils 
and  Australia. 
The  February  number  of  the  N-  S.  W.  Ayri- 
cultrial  Gazette  devote.'!  a special  article  (from 
w'hicli  we  (juote  below)  to  this  grass  which 
appears  to  be  most  commonly  know'ii  as  the 
“ Evergreen  millet.”  It  is  best  known  as  a fodder 
grass  in  the  United  States,  and  the  following  is 
a reference  to  its  growth  in  th'at  country  by 
Vasey : — 
“ This  grass  is  be.st  adapted  to  warm  climate.5, 
and  has  proved  most  valuable  on  wann,  dry  soils 
ill  the  southern  states.  Its  chief  value  is  for  hay, 
in  regions  where  other  grasses  fail  on  account  of 
drought.  If  cut  early  the  hay  is  of  good  quality, 
and  several  cuttings  may'  be  made  in  the  season, 
but  if  the  cutting  is  delayed  until  the  stalks  are 
well  grown,  the  hay  is  so  coarse  and  hard  that 
stock  do  not  eat  it  readily.  The  seed  may'  be 
sown  at  any'  time  when  the  soil  is  warm  and  not 
too  dry.  Failures  often  occur  from  sowing  thq 
seed  too  early.  If  there  is  danger  that  the  soil 
should  dry  out  before  the  seed  can  germinate, 
soaking  the  seed  may  be  resorted  to  with  good 
