THE ECOLOGY OF THE VEGETATIVE ORGANS 
INTRODUCTORY 
In view of the fact that Ruppia is a submerged plant, living under 
water at all seasons of the year, and unable to live out of it, a 
study of the methods by which it accommodates itself to this life 
is of interest, especially when one compares it with a typical land 
plant. 
Of course, in a comparison of these two types, the one point of 
vital importance to be noted first of all is the radical difference in 
the nature of their environment: the land plant pushes its stem 
and leaves into the air, a gaseous medium; while the submerged 
plant extends its shoots entirely surrounded by water, a liquid medium. 
The striking formal, structural, and physiological dissimilarities 
which obtain between land and submerged plants have their fun- 
damental origin in the physical differences of these two media and 
the concomitant variations in quality and intensity of light, temper- 
ature, &c. These physical factors have already been clearly stated 
by Warming (1902, pp. 127 ff.), Schimper (1898), and others, so that 
it is unnecessary to recount them here. 
On account of the various methods of ecological classification 
by different authors, the assignment of Ruppia to a definite ecological 
group is not as easy as might seem at first sight. Among his four 
ecological groups Warming (1902, p. 121) defines the hydrophytes 
as being those plants that are surrounded wholly or for the most 
part by water, and those that grow in very moist earth. Of the 
subdivisions of this group the “Enalid society or sea grass vege- 
tation” includes such plants as Zostera, Cymodocea, Phyllospadix, 
Potamogeton, Althenia, Ruppia, Xc. (1. c. p. 156). 
More recently, however, a tendency has been manifested to re- 
strict the term hydrophytes to plants of fresh water only (e. g. 
Atkinson, 1905, p. 484). According to this view Ruppia is excluded 
and must be classified as a halophyte, an arrangement which seems 
reasonable, if one accepts the literal meaning of the term “halo- 
phyte.” 
As a matter of fact, a study of the plant shows that the great 
majority of its adaptive characters fit it for membership in the 
hydrophytes, and only a few—possibly not more than one or two 
—features added to its hydrophytic characters would qualify it for 
