In  

angiosperms,  

the  

male  

sex  

organs  

(stamen)  

and  

female  

sex  

organs

(pistil)  

are  

borne  

in  

a  

flower.  

Each  

stamen  

consists  

of  

a  

filament  

and  

an

anther.  

The  

anther  

produces  

pollen  

grains  

(male  

gametophyte)  

after

meiosis.  

The  

pistil  

consists  

of  

an  

  

ovary  

enclosing  

one  

to  

many  

ovules.

Within   

the   

ovule   

is   

the   

female   

gametophyte   

or   

embryo   

sac   

which

contains  

the  

egg  

cell.  

The  

pollen  

tube  

enters  

the  

embryo-sac  

where

two  

male  

gametes  

are  

discharged.  

One  

male  

gamete  

fuses  

with  

egg

cell  

(syngamy)  

and  

other  

fuses  

with  

diploid  

secondary  

nucleus  

(triple

fusion).  

This  

phenomenon  

of  

two  

fusions  

is  

called  

double  

fertilisation

and  

is  

unique  

to  

angiosperms.  

The  

angiosperms  

are  

divided  

into  

two

classes – the dictyledons and the monocotyledons.