388 Cooke and Schively on Observations on the 



nucleus and the amount of cytoplasm (Fig. 12). The lower 

 cell has a much larger mass of dense cytoplasm. Its 

 nucleus is very large, and contains a large dense nucleolus, 

 while strands of chromatin pass through its clear cavity. It 

 is this cell that later gives rise to the main mass of the 

 embryo. The upper cell only forms a small, suspensor-like 

 structure of four or five cells. During this two-celled stage 

 of the embryo, there is little differentiation between embryo 

 cells and albumen cells. But as development progresses, the 

 difference constantly increases. The embryo cells become 

 relatively much smaller and denser-looking. The albumen 

 cells enlarge greatly, stain less and less densely and finally 

 develop a great quantity of starch. They also continue to 

 increase somewhat in number by division. 



The lower embryo cell then divides in a plane perpen- 

 dicular to the first division, giving two nuclei that lie side 

 by side (Fig. 13) and later separate by a vertical cell wall. 

 Then these two cells each divide in the same horizontal 

 plane as the second cleavage, but in a direction on this plane 

 at right angles with the direction of the second cleavage. 

 The spindle observed here possessed sharply pointed ends 

 (Fig. 14). Next these four cells all divide vertically, giving 

 an eight-celled stage consisting of two tiers of four cells each. 

 Subsequently each of these eight cells divides unequally, 

 so that the axis of the spindle must lie in a radius from the 

 centre of the mass. After these cells have formed, the 

 appearance of a cross-section is as if four oblique radii were 

 passing out from the centre of a circle. On the line of each 

 radius lie two cells, the inner one smaller, the outer one 

 much larger. Later an oblique division wall appears between 

 each of these two cells. So these four division walls form 

 a diamond, within which lie four small cells, and outside of 

 which lie four much larger cells (Plate XXXII, Fig. 16). 



After this sixteen-cell stage further regularity in division 

 cannot be traced, though division proceeds rapidly. The 

 eight large outer cells frequently divide in a plane perpen- 



