THE FLOWER 133 



The slow, late deposition of the starch on the dorsal side and near the 

 embryo appears to be due to the difficulty of diffusion from the conducting 

 strand across the starch-laden cells near the furrow, and to the fact that 

 the developing embryo for a time uses for its growth some of the soluble 

 carbohydrates which would otherwise be converted into starch grains. 



Immediately behind the scutellum a layer 3-5 cells in thickness 

 becomes filled with starch, and when the final ripening occurs it shrinks 

 and forms a thin band of crushed cells (Figs. 10, n). 



Concomitant with the deposition of starch in the endosperm the cyto- 

 plasm and nuclei of the cells undergo considerable change. In the earliest 

 stages the cytoplasm fills the cells ; as the latter grow and expand it forms 

 a lining inside the cell walls and surrounds the large central vacuoles ; 

 the oval nuclei lie close to the walls, and there are no visible reserves in 

 the cells. Later, starch grains are formed in enormous numbers as 

 already described, and are packed closely in the cell-cavities. 



In practically all the endosperm cells in which starch is accumulated 

 the protoplasmic contents die and become more or less disorganised. 

 The nuclei lose their nucleoli and clear outline and show other signs of 

 degeneration even before the cells are crowded with starch grains. Sooner 

 or later they become squeezed into the spaces between the densely 

 packed grains, and when stained appear in optical section as irregular 

 stellate or reticulate structures, coarse at first when the interstices are 

 comparatively wide, but in the dessication which occurs during ripening 

 the starch grains are forced closer together and the nuclear star or reticulum 

 then appears composed of thin rays of tangled strands. 



In the parts previously mentioned as the last in which starch is 

 accumulated the nuclei are not so severely crowded, and some of them 

 may retain their round or oval form even up to the time of ripening of 

 the grain ; few, however, escape the crushing described. 



The rest of the protoplasmic contents of the cells is similarly forced 

 into the spaces between the starch grains, the latter then appearing to be 

 imbedded in a matrix of protein. 



(v.) The Development of the Embryo. After a rest of a few hours the 

 fertilised ovum divides into two cells by a transverse wall, the large basal 

 suspensor cell apparently undergoing little or no further division. 

 Brenchley states that the first division takes place about five days after 

 pollination ; it is doubtless influenced by atmospheric temperature and 

 other factors, for I find that it frequently occurs about forty to fifty hours 

 after pollination. The upper cell, from which the embryo develops, 

 divides by a wall parallel to the first, and then by a wall at right 

 angles through both the cells produced, giving rise to a five-celled embryo 

 (Fig. 1 06). 



By further division in all directions the latter rapidly increases in size, 



