144 A. H. Graves, 
According to my own observations, which agree in the main 
with those of Roze (1894), the process of pollination takes place 
about as follows. Soon after the extension of the peduncle above 
the surface of the water, the anther sacs split open by a longitudinal 
cleft, and the pollen, shed in large yellowish masses, may be seen 
floating on the surface of the water. 
Immediately subsequent to the shedding of the pollen, the rhachis, 
which up to this time has been erect, commences to incline toward 
the surface of the water. It becomes more and more horizontal 
until eventually, after two or three hours, it comes to le on the 
surface of the water. 
In this position, the stigmas are of course so situated that the 
floating pollen grains, with which, in the height of the flowering 
season, the water is fairly well covered, have easy access to them. 
The final step occurs when the currents of water, always moving 
in one direction or another in a tidal ditch—or sometimes set in 
motion by gusts of wind—bring the pollen grains into contact with 
the stigmas. 
Wylie (1904), has described a similar mode of pollination in 
Elodea. He attributes the floating of the pollen-grains to the air 
imprisoned between the spines of the pollen-grain and the surface 
of the water, this being sufficient to keep the grain afloat. Pol- 
lination on the surface of the water also takes place in Vallisneria, 
as is well known. In Zostera, however (Strasburger, 1908, p. 258), 
pollination is performed below the surface of the water. 
FERTILIZATION 
No investigator has yet been able to demonstrate the process of 
fertilization in Ruppia. Murbeck (1902, p. 15) has, indeed, found 
the pollen tubes in the ovary; but has been unable to distinguish 
either of the sperm-nuclei in the embryo-sac. For various reasons, 
he concludes that the act of fertilization takes place very rapidly. 
If this is true, it may account for the fact that in my own prep- 
arations I also have been unable to find any unmistakable evidence 
of the sperm-nuclei. 
As is shown in Pl. X, figs. 62-66, a definite stylar canal exists 
from the stigma to the cavity of the ovary, but Murbeck (1902, 1. c.) 
claims that the pollen tubes, however, penetrate through the cellular 
structure of the style to the cavity of the ovary. 
