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

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

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

 and plerome differentiated ; x 216; X', the lateral stem-tip ; x 140; ^longitudinal 

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



191 



