THE EMBBYO-SAC IK ANGIOSPEBMS. 543 



Figs. 3 & 4. Longitudinal section of a nucellus of the same stage. Fig. 4 is 



drawn at a focus a little higher than fig. 3, and the central series of 

 cells are really cells which surround the axial row and embryo-sac. 



5 & 6. The embryo-sac commences to absorb the cap-cells and those 

 around. 



7. The upper nucleus has divided into four new nuclei, arranged in a te- 



trahedron. A similar group faintly discernible below. 



8. One nucleus from the upper group travels down, and three remain to 



form an egg-apparatus. 



9. The embryo-sac contains an egg-apparatus above, three antipodal cells 



below, and two nuclei are commencing to fuse in the central part. 



10. A slightly later stage showing the egg-cell and two M synergidse " form- 



ing the egg-apparatus : the two nuclei are not yet fused. 



11. The two nuclei have blended into one bright spherical " nucleus of the 



embryo-sac." 



Plate XX. 



Alisma plantago. 



Fig. 1. Ovule and embryo-sac in longitudinal section. The nucleus at the mi- 



cropyle end of the sac has divided into four, that at antipodal end 

 into two new nuclei. The cells of the nucellus are suffering absorp- 

 tion, but still show arrangement into groups radiating outwards. 



2. Ovule at time of fertilization ; a pollen-tube in the micropyle. The 



swollen appearance of egg-apparatus, two approaching nuclei in the sac, 

 and antipodal mass is due to ammonic hydrate used in preparation. 



3. Similar section : the large nucleus in centre is from fusion of two. 



Treated with ammonic hydrate. 



4. Fertilized ovule in longitudinal section : showing an embryo at micro- 



pyle end of the capacious embryo-sac, which has been cut into, and 

 its walls torn. 



Plate XXI. 



Anemone japonica. 



Fig. 1. Three young ovules, each with its carpellary leaf on the receptacle ; a 



central row of cells is evident. 



2. Older rudiment in longitudinal section : the mother cell of embryo-sac 



already distinguished by its contents. 



3. Still older rudiments raised by upgrowth of the carpel : the embryo-sac 



mother cell of the lower one has divided once. 

 3 a. Enlarged view of the lower ovule of fig. 3. 



4. Similar preparation (slightly younger), showing tendency of subepidermal 



nucellu s-cells to radiate outwards. 



5. Longitudinal section of nucellus of slightly older ovule : the embryo-sa 



mother cell has formed two " cap-cells" above. 

 6 & 7. The two " cap-cells" becoming laterally compressed and destroyed 



by surrounding cells. 

 8. Longitudinal section of nucellus of similar ovule ; two nuclei in lower 



large cell. The cap-cells are destroyed, a dark line alone representing 



them : radiating groups of cells evident. 



LINN. JOTTBN. — BOTANY, YOL. XYTI. 2 B 



