PHYSIOLOGY OF THE FLOWER. I3I 
and, close to these, minute bud-like structures. These are the 
cleistogamous flowers ; their anthers are so placed that the pollen 
grains can send their tubes straight to the stigma. Such a flower 
produces, perhaps, only two hundred pollen grains, as opposed to 
some thousands in an ordinary blossom. 
Fertilization results in changes in the egg-cell, nucellus, in- 
teguments, carpels, and frequently other parts as well. The 
fertilized egg-cell gives rise to an embryo, the primary root of 
which is directed towards the micropyle. Nutritive substances 
are formed in the nucellus, known as albumen. This is endosperm 
if produced in the embryo sac, perisperm if originated outside it. 
Seed-coats are developed from the integuments, while enlargement 
and other changes in the carpels, &c., give us fruits. 
Motility, irritability, and spontaneity have been sufficiently 
illustrated by-the movements often performed in connection with 
pollination. 
