DEVELOPMENT. 103 



single large megaspore. This cell elongates to form the embryo-sac. 

 Returning to the stage in which only the archesporial cell is found, we note 

 an elongation of cells in the center of the funiculus which foreshadows the 

 vascular bundle. This was seen in an ovary of N'. odorata 0.6 cm. in 

 diameter ; the ovules were just visible to the naked eye. In an anther 

 from the same flower the microspores are formed, but have not received 

 the characteristic markings on the exine ; the tapetum appears as a layer 

 of disintegrated matter around the walls of the anther cell ; the thicken- 

 ings are not yet laid down in the anther wall. After this the ovule rapidly 

 grows to its mature form. The outer integument becomes three cells 

 thick and loses its protoplasm, while the inner integument consists of two 

 layers, of which the inner alone remains richly protoplasmic. The nucel- 

 lus consists of many cells arranged in radial rows ; the outer ones are 

 tangentially flattened, the central ones rounded. The raphe is prominent 

 and is traversed by a slender vascular bundle with a spiral trachaea on the 

 side next to the nucellus. The funiculus is covered at base with a glandu- 

 lar epidermis like that of the ovary, but the glandular cells end at a sharp 

 line near the seed, beyond which the epidermis is plain and smooth. 

 Between the epidermis and the vascular bundle the round parenchyma 

 cells enclose large intercellular spaces. The embryo-sac (Fig. 47) is 

 prominent as a clear area below the micropyle, and is shaped like a flask 

 with the neck extending down into the axis of the seed. The ratio of the 

 diameter of the body and neck of the flask is as 5 to i in N. odorata and 

 zanzibaricnsis, but in N. lotus the whole ovule is longer and narrower, and 

 the embryo-sac is lanceolate in longitudinal section, with rounded ends. 

 A single layer of columnar nucellar cells covers its outer end. 



A day or two before the flower opens the egg apparatus is complete. 

 The embryo-sac is slightly narrowed at the micropylar end, where it is 

 covered, as before, with one layer of columnar cells. In this upper part 

 of the sac three similar cells are crowded, two above and one below. The 

 rest of the sac is lined already by a few cells around the sides, visible 

 only in my preparations as compressed nuclei. Hofmeister (1858) doubt- 

 less referred to the same thing in Nuphar, " whose embryo-sac," lie says, 

 " even before fecundation shows clearly a cellular wall " (Zellstoffhaut). 

 A pair of nuclei indistinctly seen in the extreme end of the narrow inner 

 part of the sac in N. odorata doubtless represent the antipodal cells; a single 

 cell with very large nucleolus occupies the same position in N. zanzibariensis. 

 The outer integument now consists of two (or near the raphe three) layers 



