272 



MORPHOLOGY 



established when that cell divides and forms the hypophysis. While 

 this method of embryo formation may be regarded as characteristic of 

 dicotyledons, there are numerous variations, conspicuous among which 

 are the following: 



Variations. — The proembryo may be a spherical mass of cells (as in 

 the water lilies), in" which the growing points are organized, but with 

 little or no differentiation of a suspensor. 



Figs. 600-603. — Development of embryo of Capsella (a dicotyledon) : 600, the 

 filamentous proembryo, in which the terminal cell has divided and the basal cell has 

 become large; 601, later stage, in which the terminal cell has divided to octants; 

 602, later stage, in which the dermatogen has been cut off; 603, later stage, in which 

 plerome (shaded) and periblem (between pleromc and dermatogen) are distinguishable in 

 the hypocotyl region; hypophysis (divided to three cells in the figure) completing 

 periblem (by inner cell) and dermatogen (by two outer cells). — After Coulter and 

 Chamberlain. 



In other cases the proembryo is massive, but of no definite form, filling 

 the micropylar end of the embryo sac. 



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