June, 1904.] The Embryo-sac and Embryo of Nelumbo, 171 



the embryo (Fig. 33.) Both the cotjdedonar}' ridge and the 

 incipient stem tip come from the outer end of the embryo and 

 probably represent terminal structures, but the stem tip represents 

 the more central mass of cells. On account of the spherical con- 

 dition of the embryo it is practically impossible to trace the origin 

 of any set of cells which appear at the outer end of the more 

 mature embryo, and the cotyledonary ridge maj- be lateral. 



After the cotyledonary lobes have become greatl}- enlarged the 

 incipient plumule continues its development. It grows downward, 

 forcing its way into the center of the mass of endosperm which 

 lies between the two cotyledonary lobes. The first leaf and stem 

 tip develop side by side from the terminal mass of cells in the 

 protruberance. The leaf arises on the side opposite the cotyle- 

 donar)' ridge (Fig. 34). The second leaf arises on the side of 

 the plumule opposite the first and develops more slowh' than the 

 first leaf. The comparative growth and manner of development 

 may be seen from Figs. 35-40. The radicle has its origin at the 

 base of the plumule. It is a vestigial organ and does not develop 

 on the sprouting of the seed. It can only be seen at a late stage 

 of development and is enclosed by an outgrowth from the sur- 

 rounding tissue (Fig. 40). 



The homology between the development of the embryo of 

 Nelumbo and other monocot3dedonous embryos is very striking 

 in many respects. In its early development the embryo of Ne- 

 lumbo is very similar to those of Aglaonema, Diffenbachia, and 

 Lysichiton. In these forms the oospore does not cut off a suspen- 

 sor cell but builds up a spherical embryo as is formed in Nelumbo. 

 In the forms described by Campbell, the egg may segment, first, 

 by two transverse divisions before any vertical division, or a reg- 

 ular quadrant may be formed, which is likewise true in Nelumbo. 

 The development of the " cotyledonar}' " ridge shows a striking 

 re>emblance to the hypocotyledonary expansion of various Helo- 

 biae. The mature embryo may thus be compared wath those of 

 Halophila, Ruppia, Zostera, and Phyllospadix. In these forms 

 there is a broad expansion of tissue below the plumule. In Halo- 

 phila, Ruppia, and Zosteria, the hypocotjdedonary lobe is contin- 

 uous, while in Phyllospadix the structure is somewhat lobed if 

 one may judge from the published figures and descriptions. The 

 plumule with the so-called cotyledon is attached near the center. 

 It is probable that the broad two-lobed expansion of tissue in the 

 Nelumbo embryo commonly known as the cotyledons, is a true 

 hypocotyledonary body as in the forms just mentioned. It bears 

 a rather close resemblance to the hypocotyledonar}' expansion of 

 Phyllospadix. If such a comparison is correct, the first leaf of 

 Nelumbo is homologous with the so-called cot3dedon in Ruppia 

 and Phyllospadix, and the plumule and cotyledon of the.se forms 

 may arise as terminal structures side by side, as do the plumule 



