FIG. 83. Sagittaria variabllis. 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 ; 7, later stage, with dermatogen, periblem, 

 and plerome differentiated ; x 216; D, the lateral stem-tip ; x 140; .", longitudinal 

 section of a ripe seed ; x 26. After ScHAFFNER. 43 



191 



