738 
THE  TROPICAL  AGRICULTURIST. 
[May  I,  1896. 
(ho  seed  to  the  embryo  or  plautlet.  Assuming  the 
perfect  maturation  of  a seed,  certain  conditions  are 
necessary  to  quicken  its  dormant  vitality;  and  the 
two  principal  factors  are  heat  and  moisture,  varying 
enormously  in  amount  for  ditferent  plants,  and 
acting  much  more  rapidly  on  some  seeds  than  on 
others,  even  when  the  amount  required  is  n,uch  the 
same.  Neither  under  natural  nor  under  auilicial 
conditions  will  some  seeds  retain  their  vitality  more 
than  one  season ; and  all  the  resources  of  the 
accumulated  experience  of  seed-impoitcrs  from  dis- 
tant countries  are  insufficient  in  some  cases  to 
maintain  their  vitality.  It  is  not  altogether  because 
the  interval  between  the  dispersal  and  the  gorui illa- 
tion of  the  seed,  under  ordinary  conditions,  is 
necessarily  longer ; but  rather  because  in  the  one 
case  the  condiiions  under  which  a seed  will  germinate 
are  much  more  restricted  than  in  the  oilier.  Lot 
us  now  examine  the  natural  conditions  under  which 
seeds  are  commonly  produced  and  dispersed,  in 
relation  to  the  retention  of  their  vitality ; and  w'e 
shall  learn  how  much  more  it  depends  on  their 
nature,  or  natural  means  of  protection,  than  on  tlie 
seasons.  An  oak  tree  sheds  its  acorns  in  autumn, 
and  the  leaves  which  fall  afterwards  alford  them 
some  protection  from  frost  and  excessive  dryness. 
But  the  leaves  might  be  blown  away  from  one  spot, 
and  the  acorns  exposed  to  intense  frost  or  drought, 
either  of  which  will  speedily  kill  them.  In  another 
spot  the  leaves  may  drift  into  tnick  layers,  with  an 
excessive  accuniulatijn  of  moist  tre,  causing  decay 
of  the  underlying  acorns;  and  there  are  many  otlier 
unfavourable  conditions  which  may  destroy  the 
vitality  of  the  acorn.  It  is  apparently  impossible, 
however,  to  preserve  an  acorn’s  vita  ity  by  any 
artiticiat  means  for  more  than  one  season. 
•I'he  scarlet-runner  bean  loses  its  germinativo 
power  on  exposure  to  compara'.ively  slight  frost, 
the  dec'ree  dep  nding  upon  the  amount  of  moisture 
in  it"  yet.  it  will  retain  its  vitality  for  an  almost 
indehnite  period  under  favourable  artificial  condiiions. 
In  both  of  the  examples  given,  germination  would 
naturally  follow  as  soon  after  maturation  as  the 
conditions  allowed.  The  seeds  of  the  hawthorn 
behave  differently.  Each  haw  contains  normally 
tluxe  to  five  seed's,  every  one  of  which  is  encased 
in  a hard,  bony  envelope,  in  additi  n to  Us  proper 
coat  or  testa.  Couiniitted  to  the  earth,  and  uuder 
the  most  favourable  conditions,  these  seed  do  not 
germinate  till  the  second  year,  and  often  not  so 
soon  In  this  instance  prolongation  of  vitality  is 
probably  due  in  some  measure  to  the  protective 
nature  of  the  shell  enclosing  the  seed. 
lieturning  to  seeds  in  which  the  embryo  or  plantlet 
forms  only  a very  small  part  of  the  whole  body, 
wheat  may  be  taken  as  a familiar  and  easily  ob- 
served illustration  of  a seed,  the  vital  energy  of 
which  requires  very  little  to  stimulate  it  into  active 
growth;  and  yet  this  same  seed,  having  no  special 
proteUi.n  in  the  way  of  coating,  will  retain  iti 
vitality  as  long,  perhaps,  as  any  kind  of  seed,  if 
not  under  the  influence  of  moisture,  ihe  primary 
condition  to  ibe  preservation  of  vitality  in  a seed 
is  perfect  ripeness.  Unripe  seeds  of  many  kii,ds 
will  germinate  and  grow  into  independent  plants  if 
sown  immediately  after  removal  from  the  parent. 
The  facility  with  which  immature  wheat  will  ger- 
,tinate  is  most  disastrously  exemplified  in  a wet 
Wvest  when  the  seeds  will  sprout  while  the  corn 
standing  or  in  sheaf;  thus  destroying  more  or 
less  completely  the  value  of  the  gram  or  flour,  as 
ihe  starch  or  flour  is  consumed  in  the  development 
of  the  embryo,  or  what  is  left  is  so  deteriorated 
bv  chemical  change  that  it  is  not  good  lor  food. 
There  is  perhaps  no  other  seed  more  susceptible 
to  moieturl  and  none  less  affected  by  dryness,  or 
u Wont  nr  cold  in  the  absence  of  moisture. 
'^^The  kind  of  vivipary  exhibited  by  the  wheat  is 
occasionally  observed  in  various  other  plants;  and 
Bomelim.  s the  seeds  of  pulpy  fruits  germinate  in 
tlm  fruit  There  is  also  a class  of  plants  in  which 
vivlnuv  is  noinial.  rvomineiit  in  this  class  arc  the 
n vngroves  [Ithizophoreo-,  Ac.)  of  muddy  sea-shores 
1 the  tropics.  In  these  plants  there  is  a reniark- 
ndantation  to  conditions,  which  ensures  their 
.t^rodSu  iTom  the  very  inception  of  the  embryo 
there  is  no  apparent  iiitorriiption  of  active  vitality 
in  its  development  and  germination.  In  the  earliest 
stage  the  cotyledons  or  seed-leaves  are  formed, 
and  the  radicle  or  future  pi  imary  root  is  represeincd 
by  a very  small  p int.  When  the  former  have 
attained  their  hill  development,  which  is  not  great, 
the  iaticr  begins  to  grow  and  mpidly  incre-ses  in 
size.  Each  fruit  or  seed-vessel,  it.  siionld  be  men- 
tioned, contains  only  one  seed,  the  rootlet  of  which 
points  to  the  apex  of  tiie  fruit.  Soon  th  s rootlet 
pushes  its  way  through  the  apex  of  the  fruit,  and 
grows  into  a spindle-shaped  body  of  great  density 
and  length  ; the  cotyledons  or  seed-leaves  remaining 
partly  inside  the  fruit,  and  acting  as  an  organ  of 
absorption  from  the  parent  plant  to  noniish  the 
seedling.  In  Ji/nxophora  nnicronala  this  radicle 
attains  a length  of  two  or  three  feet,  and  the  seedling 
eventually  fail.s,  and  by  its  own  weight  penetrates 
and  sticks  in  the  mud,  leaving  the  fruit,  containing 
the  exhausted  cotyledons,  attached  to  the  tree,  where 
it  dries  up.  Another  singular  adaptation  to  condi- 
tions is  tlie  vital  development  of  the  seeds  of  aquatic 
plauts  which  ripen  their  seeds  on  or  under  water. 
, Vallisneiia  is  a remarkable  instance  of  this.  The 
unisexual  flowers  are  formed  under  water;  the 
female  on  long  coiled  stalks,  which  at  the  right 
period  uncoil,  and  the  flower  rises  just  above  the 
surface  of  the  water.  Simultaneously  the  sliort- 
stalked  male  flowers  are  detached  from  the  base 
of  the  leaf-stalks,  and  also  rise  to  the  surface. 
After  impregnation  has  taken  place,  the  stalk  of 
the  female  flower  coils  up  again,  and  draws  the 
s’ed-vessel  down  under  water,  where  the  seeds  ripen. 
It  has  been  explained  that  heat,  moisture,  and 
air  are  necessary  to  the  germination  of  seeds, 
varying  immensely  for  different  seeds.  We  corns 
now  to  the  behaviour  of  certain  seeds  under  the 
i:  fluence  of  an  unusual  or  unnatural  amount  of 
moisture,  I cat  or  cold  especially  m relation  to  the 
length  of  the  duration  of  the  exposure  to  any  one 
of  these  factors.  It  has  been  proved  beyond  dispute, 
by  actual  experiment,  that  the  vitality  of  certain 
seeds,  notably  various  kinds  of  beau  and  convolvulus, 
is  not  impaired  by  immersion  in  soa-waler — or  rather 
floating  and  partially  submerged — for  a period  of  at 
least  one  year  ; and  that  after  having  been  Iccpt 
quite  dry  for  two  or  three  years.  Plants  are  act- 
ually growing  at  Kew  from  seeds  treated  as  des- 
cribed; and  some  years  ago  several  seeds  oi  Kntada, 
cast  ashore  in  the  Azores,  whither  they  had  been 
transported  by  the  Gulf  Streim,  were  raised  at 
Kew.  So  far  as  at  jiresent  known,  all  the  seeds 
that  will  bear  very  long  immersion  without  injury 
have  an  intensely  hard,  bony,  or  ciustaceons  coat, 
that  would  wilh.staiid  lioiling  for  a minnie  or  t'vo 
without  killing  the  embryo.  A'et  it  is  difficult  to 
unrlcrstand  this  power  of  resistance,  especially  after 
being  kept  dry  for  a long  time.  This  impreviousness 
to  water  explains  the  wide  distribiilion  of  many 
sca-side  plants,  the  seeds  of  which  are  conveyed 
by  oceanic  curienls.  How  long  such  sc  ds  would 
retain  their  vitality  in  water  is  uncertain,  because 
experiments  have  not  reached  the  limit.  Many 
readers  will  remember  Darwin’s  experiments  in  this 
connection;  but  it  should  be  borne  in  mind  that  they 
were  chiefly  with  seeds  of  jilaiits  not  at  all  likely 
to  be  dispersed  by  the  sea. 
It  has  already  been  stated  that  some  seeds  will 
bear  immersion  in  boiling  water  for  a short  time, 
and  gardeners  occasionally  practise  this  treatment 
to  accelerate  the  germination  of  hard-coated  seeds. 
But  seeds  of  all  kinds  will  hear  for  a considerably 
longer  period  a much  higher  dry  temperature  than 
soaking  in  water  of  the  same  temperature.  It  is 
recorded,  by  tru.stworthy  authorities,  that  tlie  seeds 
of  many  plants — poppy,  parsley,  sunflower,  and 
various  kinds  of  grain,  for  instance — it  perfectly  dry, 
do  not  lose  their  vitality  when  subjected  to  a ten'i- 
perature  of  212°  E.  for  forty-eight  hours ; and  for 
sliorier  periods  to  a much  greater  heat.  The  result 
ill  most  cases,  tliongii  not  all.  is  a considerable 
retardation  of  germination.  Dry  grain  is  equally 
impervious  to  cold,  lii  1877,  seedling  wheat  was 
exhibited  at  the  Liuiioau  Society  that  had  been 
raised  at  Kow  from  grain  that  had  been  exposed 
