Fig. 82. — Sagittaria variabilis. Development of embryo. A, proembryo of three cells; 

 a, basal cell (in all figures) ; &, middle cell (dividing) ; c, terminal cell from which 

 the cotyledon is derived ; *y, synergid ; _Z?, same stage, but terminal cell dividing; 

 C\ middle cell (b) has divided, s being the cell from whose derivatives the stem-tip 

 arises, and terminal cell (e) dividing; 2>, both cells derived from b are dividing; 

 L\ terminal cell has given rise to four cells (c), and the region derived from the 

 middle cell ib] has developed further; F, showing further development of the 

 middle cell region (&), while the terminal cell region has made no further progress; 

 <7, dermatogen differentiated in the terminal cell region (c), and the middle region 

 lb> further developed; H^ differentiation of dermatogen beyond the terminal region 

 (c), the middle region lb) showing the differentiation between hypocotyl ( h) and 

 region producing stem-tip; 7, more advanced stage, showing same regions as in H % 

 hut the dermatogen of the root-tip not yet formed, and the plerome and periblem 

 undifferentiated.- A-F, x 400; £, x 260; II, x 400; i, x 260.— After JSchaffnek. 43 



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