E F I J 



Fig. 67. Development of embryo sac in Podostemon ceratophyllum (A-I) and 

 Weddelina squamulosa (J,K). A, Podostemon, l.s. ovule, diagrammatic. B, l.s. 

 young ovule, showing archesporial cell. C, older stage, showing formation of 

 psuedo embryo sac by disintegration of nucellar cells lying just below the mega- 

 spore mother cell. D, formation of dyad cells. E, degeneration of upper dyad 

 cell. F, two-nucleate embryo sac; note enlarging pseudo embryo sac. G, two- 

 nucleate embryo sac; primary chalazal nucleus disorganizing. H, primary micro- 

 pylar nucleus divided into two daughter nuclei; primary chalazal nucleus has disap- 

 peared. J, five-nucleate stage in which the primary chalazal nucleus has degenerated 

 and disappeared. (After Hammond, 1937.) J,K, Weddelina, stages corresponding 

 to I. (After Chiarugi, 1983.) 



104 



