260 PRACTICAL BOTANY 



deeply seated in the tissue of the nucellus may be recognized 

 as the embryo-sac, or macrospore. 



Cut similar sections from specimens taken later in the year : in 

 these the growth of the embryo-sac, and development of its con- 

 tents, as well as the growth of the pollen tubes, the process of 

 fertilization, and development of the embryo may be traced. 



Note the growth of the arillus, as an extra integument, pink 

 and fleshy when mature, around the base of the ovule. 



The observations of structure and development of the ovule 

 may be best conducted in material hardened in alcohol, and then 

 soaked, before cutting, in half glycerine, half alcohol. 



