Formation of Embryo 



127 



and 245). The first change that takes place (after the sur- 

 rounding of the embryonic vesicle by a cellulose coat) is the 

 division of the vesicle into two (fig. 244, 11., k) ; the upper 

 cell being developed into a suspending cord, the suspensor 

 or pro-embryo (fig. 246, et), at the end of which the embryo 

 or young plant, formed by the division of the lower cell, 

 is attached (fig. 246, e). At the same time a number of cells 

 are produced within the embryo-sac by free cell formation; 

 these are filled with nutritive materials, and are known as 

 endosperm. Sometimes nutritive cells are produced within the 

 I 



et-J=- 



Fig. 245.— Fertilisation of Cfl««a. I. Apex FiG. 246. — Formation of the embryoDf 



of the embryo-sac, e, at the time when Heliotropium : ed^ endosperm ; ei, sus- 



the poHen-tube, ps, has just come into pensor ; e, rudiment of the embryo, its 



contact with the embryonic vesicle, k. enveloping membrane being already 



II. Fertilised embryonic vesicle sepa- formed ; a, cells developed out of the 



rated. two embryonic vesicles. 



nucleus outside the embryo-sac. In this case the term perisperm 

 is employed. Very often as the embryo increases in size the 

 nutritive cells around are absorbed, until, as we have seen is 

 the case with the Broad Bean, the young plant occupies the 

 whole of the nucieus. In other cases a part of the eridosperm, 



