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MTBIOLOGY TODAY | JULY   ‘15 49

•    Carpel  :   Megasporophyll

•    Ovule   :           Integumented

                                                                                                                                                                                            megasporangium

•    Embryo sac  :   Female gametophyte

•    Egg     :   Female gamete

•    Stamen  :   Microsporophyll    

•    Pollen or   pollen grain            :   Microspore

•    Germinating    pollen  grain   :    Male   gametophyte

Homologies of flower parts

Stamen, microSporangium and

pollen grain

• Androecium consists of stamens as its units. The stamens
or microsporophylls are regarded as the male reproductive

organs of the flower.

• Each stamen consists of three parts - filament, anther
and connective.

• The filament is the slender stalk of the stamen, and the
anther is the expanded head, borne by the filament.

•    Each    anther consists    usually of  two lobes   connected   

together    by   a   sort    of  midrib known   as   the    connective. 

Each     lobe    of  the     anther contains    two pollen sacs or  

microsporangia; thus    there   are     four    pollen  sacs    or  four    

microsporangia  in   each    anther.

•    Such   anthers having  2   anther  lobes   and     4   microsporangia  

are  called dithecous anthers   or  two celled anthers. 

However,    at   maturity,  two  microsporangia of   an  anther lobe

get  united by   dissolution    of   partition  wall     between    them.

•    In  some   plants  e.g.,   china   rose,   anther  is  having  only    single  

anther  lobe    and     2   microsporangia  instead of  4.  Such    anthers are 

called  monothecous anthers or  one celled anthers. A   rare    

case     is Arceuthobium,   where   there   is  only    one     microsporangium 

per  anther     i.e.,   monosporangiate condition.

•    The    young   anther  is  a   homogeneous mass    of  meristematic    

cells   surrounded  by  an  epidermis.  Soon    groups  of  hypodermal  

cells   in  each    of  the     four    corners become  distinguished   from    

the  surrounding    cells    by  their   large   size,  dense   cytoplasm

and  prominent  nuclei.

•    These  cells,  which   are  arranged   in   plate-like or   crescent-

shaped  vertical    rows,   form     the    archesporium    of  the 

anther.

•    The     archesporial   cells    enlarge    radially    and  divide periclinally

resulting   into     outer  primary parietal cells  and     inner   

primary sporogenous cells.  The  primary    parietal    cells   

undergo repeated    periclinal  and     anticlinal  divisions   giving  

rise    to  3-5     concentric  layers  which   eventually  from    the 

anther  wall.   The     primary sporogenous cells   function    as  

microspore  mother  cells.

Structure of microsporangium (pollen sac)

•    In  a   transverse section,    a    typical    microsporangium appears

near     circular   in   outline.   It   consists   of   two     parts   —   outer  

wall    and     central homogenous  sporogenous tissue.     The     four    

types    of  wall    layers are:

• Epidermis of single layer for protection.


• Endothecium of single layer for dehiscence of
  anther.
  • Endothecium is the sub-epidermal layer of the anther
  
  wall. Mostly there is a single layer of endothecium, but
  sometimes, as in Coccinia indica, it is two layered. The
  cells of endothecium are radially elongated and attain
  
  their maximum development when pollen grains mature.
  The radial and inner tangential walls of these cells have
  
  characteristic fibrous thickening bands. Usually these
  
  bands are U-shaped or ring shaped, but in Melothria
  maderaspatana they occur in the form of two overlapping
  spirals. These bands are formed at the expense of the
  
  starch stored in endothecial cells.