102 



The Waterlilies. 



each consisting of a single straight row of cells. They are removed four 

 or five cells from the inner epidermis and seven to twelve cells from the 

 outer epidermis, and between each pair of lines eight cells intervene. The 

 cells immediately surrounding the archesporia take on a more or less 

 concentric arrangement, and the development goes on in the usual way 

 for flowering plants. In N. caerulea the outer stamens develop slightly in 

 advance of the inner ones ; where the former are 1.3 cm. long and the 

 spore-mother-cells are already separate from one another and becoming 

 rounded off, the mother-cells of the inner stamens form a continuous tissue. 

 The ovules originate after the ovary has attained a considerable size, 

 say 0.5 cm. in diameter in N. caerulea. At first a tiny rounded column 



Fig. 4. Ovule of N. odo- Fio. 47. Embryo sac of N. odorata; longitudinal section of ovule at time of 



rata, from a half-grown bud, flowering. From a photomicrograph, 

 showing archesporium. 

 From a photomicrograph. 



projects into the enlarging ovary cell. This swells at the end into a 

 knob, an integument of two cell-layers grows up around the knob, and 

 then a second integument outside the first. When the inner integument 

 has reached the height of the nucellus, the outer one is about half as high 

 (cf. Fig. 46). Meanwhile the knob has turned over at right angles to the 

 supporting column in its change toward anatropy. A large archesporial cell 

 is now visible at the apex of the nucellus, covered by a layer of cells. The 

 archesporial cell presents five times as large a surface in longitudinal sec- 

 tion as the surrounding cells ; its nucleus is as large as an entire cell of 

 the nucellus, is rather poor in contents, and has a single dense nucleolus. 

 Its further development has been described for N. odorata by Cook (1902). 

 According to his account, a tapetal cell is cut off at the outer end of the 

 archesporial cell (cf. Fig. 46), and from the former several tapetal cells 

 arise by a variable series of divisions. Three potential megaspores are 

 next cut off from the mother-cell. These rapidly degenerate, leaving a 



