PHYSIOLOGY OF THE FLOWER. 131 



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, perisp)erm 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. 



