K L 



Fig. 53. Formation of megaspore tetrads in various angiosperms. A, Balano- 

 phora elongata, megaspore mother cell. B, dyad stage; lower dyad cell is much 

 smaller than upper. C,D, both dyad cells dividing. E,F, tetrad stage; note that 

 uppermost megaspore functions, while the other three degenerate and disappear. 

 (After Fagerlind, 1945b.) G,H, Gloriosa virescens, megaspore tetrads in which 

 every cell is binucleate. /, one of the megaspores has developed to four-nucleate 

 stage and another to two-nucleate. (After Afzelius, 1916.) J, Aristotelia racemosa, 

 two tetrads with third megaspore functioning. (After Mauritzon, 1934.) K, Rosa, 

 two tetrads with micropylar megaspores functioning. L, same, megaspore tetrad 

 with both micropylar and submicropylar megaspores enlarging. (After Hurst, 

 1931.) M, Senecio abrotanifolius, megaspore tetrad, showing two middle mega- 

 spores lying side by side. (After Afzelius, 1924) N, Culcitium reflexum, mega- 

 spore tetrad, showing micropylar as well as chalazal megaspore enlarging. (After 

 Afzelius, 1924) 



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