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GERMINATION IN PLANTS.

GERMINATION  IS  THE  GROWTH  OF   PLANT  INTO  SEEDLING.It    starts  when  seeds   become  active   below  ground , and  ends   when   the  first  foliage     leaves  appears  above  the  ground  .A  seed  consists  of  an  embryo  and  the  food  store ,surrounded    by    a   testa  (seed coat). The  embryo   is   made  up  of   one  or  two  cotyledons (seed leaves),attached   to  a  central  axis  .The  upper  part  of  the axis   consists  of  an  epicotyl,which  has  a  plumule (embryonic   shoots),  at  its  tip.The  lower  part  of  the  axis     consists  of  hypocotyl  and  a  radicle (embryonic  root). After  dispersal  from  the  parent  plant  ,  the  seeds   dehydrate  and  enter  a  period of  dormancy .Following  this  dormant  period  , germination   begins , provided   that  the  seeds  have  enough  water,  oxygen,warmth   ,and  in  some  cases,light.In  the  first  stages  of  germination  ,the  seed  takes  in  some  water;the  embryo  start   to  use  its  food  store ;and  the  radicle  swells  , break through  the testa,  and  grows  downwards.Germination   then  proceeds  in   one of two  ways  depending  on  the  type  of  seed .In  epigeal  germination  ,the hypocotyl  lengthens  ,pulling the plumule  and  its  protective  cotyledons  out  of the  soil .In   hypogeal   germination  the  cotyledons  remain  below    ground  and  the  epicotyl lengthens,pushing  the  plumule   upwards.

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