FORMATION OF THE SEED ° ay 
CHAPTER: x 
FORMATION OF THE SEED 
Tue fruit and seeds are the result of fertilisation, which 1s 
preceded by pollination. Fertilisation cannot take place until 
the ovule is ready to receive the contents of the pollen grain. 
Structure of When quite young an ovule consists of: (1) a 
Ovule. stalk, (2) two integuments or coats, (3) a central 
portion, the sporangium or nucellus. Between the integu- 
ments a passage is left, through which the pollen tube 
makes its way in order to 
reach the sporangium. This 
passage is called the mucropyle, 
and may usually be seen asa 
small hole in the testa of the 
seed. (See Pio. 1 mj) Ag 
the ovule develops a macro- 
spore or embryo-sac 1s formed 
in the sporangium ; from the’ 
macrospore the oosphere’ — 
arises, and until this has 
been formed the ovule is not One : 
ready for fertilisation. m, micropyle; int, integu- 
When the oosphere is ready, ee oe 
the contents of the microspore 
or pollen grain, which must have previously been deposited 
on the stigma, pass down the pcllen tube put out by the 
pollen grain and unite with the oosphere. After this union, 
known as fertilisation, the oosphere begins to develop into 
the embryo. The result of fertilisation is: (1) the formation 
of the embryo, (2) the formation of endosperm or food 
material around the embryo, so that the whole macrospore 
is used up. 

