100 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



In Convallaria majalis (Stenar, 1941) the first division of the 

 megaspore mother cell results in the formation of the usual dyad 

 cells (Fig. QQA,B). Walls are also laid down after the second 

 division (Fig. 66C), but these soon break down so that the dyad 

 cells are again restored although each of them is now binucleate 



B 



D 



Fig. 64. Development of embryo sac in Machaerocarpus calif ornicus. A, mega- 

 spore mother cell. B, dyad stage; nucleus of lower dyad cell dividing. C, two- 

 nucleate embryo sac with remains of degenerated upper dyad cell. D, four- 

 nucleate embryo sac. E, six-nucleate embryo sac; lower two nuclei of four-nucleate 

 stage have remained undivided. F, mature embryo sac, showing two synergids, 

 egg, two polar nuclei, and single antipodal nucleus. (After Maheshwari and Singh, 

 1948.) 



