108 



Mary Gordon 



occurs in all monocotyledons ' and most of the dicotyledons. 

 Some of the nuclei later pass to the walls of the embryo-sac^ 

 where they form a single lining layer (Text Fig. II.). Portions 

 of the protoplasm around the walls, each containing a nucleus,. 

 are cut off by cell walls, so that the embryo-sac becomes lined 

 by a single layer of cells. This section is also cut to one side of 

 the ovary, so that the embryo is not showing. 





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Text Figubk II. 

 Contents of embryo-sac of barley soon after fertilisation. 

 A — Group of large vacuolate nuclei in embryo-sac. 

 B — Wall of sac lined by protoplasm and nuclei. 



A typical section through an oat grain in a later stage of 

 development than the preceding sections is shown in Text Fig. 

 III. One nucleus of the outer layer of endosperm cells is 

 undergoing mitosis, and there are also two resting nuclei of 

 the same layer apparent. After the nuclei divide, transverse 

 cell-walls are formed between them, and the inner cells do not 

 as a rule divide again, but they enlarge considerably and become 

 filled with starch. The nucleus of the outer cell remains large 



