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A TEXTBOOK OF THEORETICAL BOTANY 



<*| Outer integument 

 Inner integument 

 Nucellus 



Prothallial haustoria 



I 



1 



Prothallus 



Fig. 780. — WeUvitschia mirabilis. 

 Longitudinal section of the 

 nucellus and female prothallus at 

 the fertilization stage showing the 

 upward growth of the haustorial 

 tubes into the nucellus. 



Embryogeny. 



The zygote nucleus divides and the two daughter nuclei become sur- 

 rounded by walls to form a two-celled pro-embryo. The upper cell is the 



Fig. 781. — Welwitschia mirabilis. Ripe seeds showing the wings. 



