DEVELOPMENT. 



105 



The earliest fertilized ovule of Nymphaea that I have seen is of 

 N. lotus, and has already reached nearly its mature size. The integuments 

 are considerably hardened, and the perisperm is loaded with starch. 

 A broad space at the micropylar end of the seed is occupied by the endo- 

 sperm, the cells of which are very thin and watery (Fig. 48, a). A distinct 

 layer of perisperm still bounds the endosperm on the side next to the 

 seed coat. From a point near the micropyle a row of three cells projects 

 into the endosperm, representing the embryo. An older seed of the same 

 species shows the endosperm occupying an approximately spherical space, 

 somewhat pointed above and flattened below ; its cells are large and 



Fio. 48. Embryology : (a), (7i) successive stages, N. lotus; (c) spherical 

 embryo with suspensor, N. odorata; (<l) early differentiation of cotyledons 

 and plumule, N. caerulea. 



distinctly nucleate, but very thin walled and poor in contents. The 

 embryo (Fig. 48, b) consists of a line of three suspensor cells and a 

 terminal knob of probably eight cells (four in longitudinal section). The 

 uppermost suspensor cell is hexagonal, the others square (in section). 

 After this the endosperm enlarges very little. As the embryo encroaches 

 upon it, the outer cells become denser and more regular until they reach 

 the mature condition, and the inner ones are crushed to a thin layer of 

 remnants between the permanent outer layer and the cotyledons. The 

 embryo proper (cf. Conard, 1902) becomes accurately spherical as it 

 enlarges, until it consists of some hundreds of cells (Fig. 48, c}. Then the 

 lower end becomes flattened by reason of the outgrowth of cells on each 

 side of the lower pole. In section the embryo now appears triangular 

 and almost equilateral. The two lobes increase symmetrically and form 

 the two equal cotyledons. At first these spread out nearly horizontally 

 (Fig. 48, flf), while in the middle between them a slight cone-like papilla 



