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 
(4897) 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. 
