No. 501] EMBRYOLOGY OF MYOSURUS MINIMUS 585 



sac divide, forming eight nuclei, four at each end of the 

 sac. The nucellus now lies parallel to the axis of the 

 receptacle with the niicropyle, which is now completely 

 formed, directed upwards (PL II, Fig. 15). One nucleus 

 from each end of the sac moves toward the center where 

 they fuse to form the definitive endosperm nucleus (PL 

 II, Fig. 17). At first this nucleus is characterized by two 

 nucleoli (PL II, Fig. 19), the others having only one. 

 Maturation is now complete, and the cell which is to be- 

 come the functional egg cell may lie between or at either 

 side of the synergids. 



The pistil has now reached its final stage. It makes a 

 slight angle with the receptacle (PL II, Fig. 15). The 

 stigmatic surface is marked by long spreading cells (PL 

 II, Fig. 16). The presence of chloroplasts in the cells of 

 the style and epidermis will be noted. The ovarian 

 cavity is almost entirely filled with the ovule. It is lined 

 with a layer of cells which represent the original epi- 

 dermal layer before enclosure took place. In surface 

 view they are seen to be irregular cells with wavy walls 

 (PL II, Fig. 24). Immediately underneath this layer is 

 one, or in some places two, layers of long interlacing cells 

 formed from the fibro-vascular bundle. They form a firm 

 basket-like structure. 



Already, even before the definitive endosperm nucleus 

 is formed, the pollen tubes are found in the micropyle. 

 About the time of the formation of the endosperm nucleus 

 the pollen tube enters the sac (PL II, Figs. 18-19). The 

 synergids at once begin to degenerate. As the tube 

 passes into the sac the egg nucleus and the endosperm 

 nucleus move towards each other (PL II, Fig. 19). The 

 cytoplasm around the egg nucleus becomes denser and 

 soon distinct from the other cytoplasm. It is not certain 

 about the conduct of the generative nuclei, actual fusion 

 stages not having been observed. Except for a few 

 isolated observations the evidence points to the fact that 

 the endosperm nucleus is fertilized by one of the genera- 

 tive nuclei and the egg nucleus by the other. The isolated 



