The Morphology of Ruppia Maritima. 164 
The embryo-sac develops in the usual way and always from the 
innermost potential megaspore, the outer ones becoming resorbed. 
The antipodal cells are surrounded by cytoplasm and a thin mem- 
brane, and are always three in number. No further divisions among 
_ them were observed. 
Male Gametophyte. The tetrads are oriented to each other like 
the four quadrants of a sphere. 
Eight chromosomes appear in the reduction-division. 
The generative cell is formed very early in the development, at 
the end of the young pollen-grain. No membrane now or later 
separates it from the rest of the grain. 
When the grain has nearly reached maturity, the generative cell 
divides, the two resulting male cells remaining united. 
The mature pollen-grain is of peculiar shape, but similar forms 
occur in other Potamogetonaceae. 
The wall of the pollen-grain is formed inside of the walls of the 
tetrads, these latter walls becoming apparently dissolved. 
The wall is never of more than a single layer. The thickenings 
on its exterior appear to be the result of depositions. At certain 
regions these depositions are omitted, and these spots are probably 
the places where the pollen-tube may commence its formation. 
Pollination. Pollination is accomplished by means of water, an 
unusual method. 
Endosperm. The endosperm is scanty, never more than a thin 
layer lining the embryo-sac, and containing free nuclei. 
Embryo. The suspensor is limited to a single large cell, which 
later develops to an enormous size. 
The embryo evidently develops from two or three primary seg- 
ments as in the typical monocotyledonous embryo. 
An unusual state of affairs exists, however, in the large number 
of early longitudinal divisions. 
Apparently both cotyledon and stem-apex arise from the terminal 
segment as in Zannichellia, but this cannot be definitely proved, on 
account of the obscurity of the segment boundaries. 
The two lower segments form hypocotyl, adventitious root, and 
primary root. 
I agree with Murbeck in locating the vestiges of the primary root 
at the base of the enlarged hypocotyl. 
Another possible interpretation is that practically the whole 
swollen area is a root, metamorphosed into a storage organ. 
