THE FLOWER 131 



becomes gradually disorganised and absorbed, its disappearance being 

 most rapid in the region of the embryo and on the dorsal side of the ovule. 

 The epidermis of the nucellus, however, continues for a long time as 

 a living tissue, its cells dividing and expanding as the ovule grows ; the 

 position, size, and regular arrangement of the cells render it extremely 

 liable to be mistaken for the aleuron layer before the latter is distinctly 

 differentiated from the amyliferous cells of the endosperm. Later, its 

 cell-contents become disorganised, the remains of the cytoplasm tending 



FIG. 104. Section of the micropylar portion of the FIG. 105. Longitudinal section of the 



embryo-sac, showing the ovum with a male gamete embryo-sac (June 16) showing 2- 



within it, four endosperm cells and p, tip of the celled embryo, endosperm cells and 



pollen-tube with the second male gamete ( x 420). the large antipodals ( x 84). 



to collect as a thin layer across the middle of the cell, where it is easily 

 mistaken for a cell wall dividing the epidermis into a double-celled layer. 

 Ultimately the radial walls of the nucellar epidermis are more or less 

 absorbed, and when the grain shrinks through the loss of water during 

 the ripening process the single-celled tissue collapses and its upper and 

 lower walls are crushed together, finally appearing in the ripe grain as a 

 highly attenuated layer, recognisable only with difficulty as a delicate 

 covering on the outer surface of the aleuron cells. 



