► 



The Morphology of Ruppia Maritima. 161 



The embryo-sac develops in the usual way and always from the 

 innermost potential raegaspore, 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. 



