FORMATION OF THE SEED 57 
CHAPTER X 
FORMATION OF THE SEED 
Tue fruit and seeds are the result of fertilisation, which is 
preceded by pollination. Fertilisation cannot take place until 
the ovule is ready to receive the contents of the pollen grain. 
eimietiro 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 mecropyle, 
and may usually be seen as a 
small hole in the testa of the 
peed. ioee fig. 1 mij os 
the ovule develops a macro- 
spore or embryo-sac 1s formed 
in the sporangium ; from the _ 
macrospore the | oosphere 
arises, and until this has 

: Fig. 69.—SECTION THROUGH 
been formed the ovule isnot — Ovary, SHow1nc OvuLes. 
ready for fertilisation. m, micropyle; int, integu- 
y 
ments ; , nucellus ; ¢.s, em- 
bryo-sac. 
When the oosphere is ready, 
the contents of the microspore 
or pollen grain, which must have previously been deposited. 
on the stigma, pass down the pollen 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. 
& 
