D 



Fig. 83. — Sagittaria variabilis. Development of embryo. A, somewhat advanced stage 

 showing the depression in which the stem-tip develops; x 216; B, about the same 

 stage, showing the entire embryo ; x 66 ; C. later stage, with dermatogen, periblem, 

 and plerome differentiated ; x 216; />, the lateral stem-tip ; x 140; £, longitudinal 

 section of a ripe seed ; x 26. — After Schaffnek. 43 



191 



