The Morphology of Ruppia Maritima. 157 



The ripened fruit has a greater specific gravity than water, which 

 one can easily demonstrate by breaking off the fruit from the stipe. 

 It then sinks immediately to the bottom, and, in most cases, probably 

 passes the winter embedded in the mud. Under such conditions, 

 the outer soft parts of the fruit-covering soon decay, leaving the 

 inner thickened portion of the ovary-wall which surrounds the seed. 

 Since this area extends up into the stylar canal, the result is an 

 appearance as in Text-fig. 31. At the end is a long beak, derived 

 from the stylar region. Such a structure is accordingly an achene, 

 its outer layer being hard, dry and indehiscent, and derived from 

 the ovary. 



A prominent beak is supposed to be a specific character of Ruppia 

 rostellata. But a comparison with the figures of Irmisch (1858) of 

 R. rostellata demonstrates that the beak represented there is not 

 any longer than that of my specimens, although of a slightly 

 different shape. 



A similar development of fruit and seed is indicated by Campbell 

 (1897) in Zannichellia, where a seed is formed surrounded by a 

 pericarp from the ovary-wall. Such achenes are also well known 

 to occur in the grasses. 



