June, 1904 .] The Embryo-sac and Embryo of Nelumho. 
171 
the embr3’o (Fig. 33.) Both the cotyledonan- ridge and the 
incipient stem tip come from the outer end of the embr5’o and 
probably repre.sent terminal structures, but the stem tip represents 
the more central mass of cells. On account of the spherical con- 
dition of the embrj'o itis practicall}' impossible to trace the origin 
of an>’ set of cells which appear at the outer end of the more 
mature embr>'o, and the cot}dedonar3' ridge ma}' be lateral. 
After the cotjdedonary 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 cotyledonar}' lobes. The first leaf and stem 
tip develop side b>' 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 slowly 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 monocotyledonous embryos is very striking 
in many respects. In its early development the embryo of Ne- 
lumbo is very similar to tho.se of Aglaonema, DifEenbachia, 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 de.scribed 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 “cotyledonary” ridge shows a striking 
re.-emblance to the hypocotyledonary expansion of various Helo- 
biae. The mature embryo may thus be compared with 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 hypocotyledonary 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 re.semblance to the hypocotyledonary expansion of 
Phyllospadix. If such a comparison is correct, the first leaf of 
Nelumbo is homologous with the so-called cotyledon in Ruppia 
and Phyllospadix, and the plumule and cotyledon of these forms 
may arise as terminal structures side by side, as do the plumule 
