328 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Fig. 188. Development of aposporic embryo sacs in Hieracium excellens (A-E) 

 and H. flagellare (F-H). A, nucellus, showing tetrad of megaspores; note enlarge- 

 ment of cell lying just below chalazal megaspore. B, megaspore tetrad in process 



