116 A. H. Graves, 
a halophyte. And when one reviews the strikingly diverse char- 
acters exhibited by plants living in salty soil—which is the vegetation 
one naturally thinks of as halophytic—and by those living in salt 
water, it seems best to avail ourselves of Schimper’s (1898, p. 817) 
terms “land halophyte” and “ water halophyte” as a solution of the 
difficulty. 
Considered as a water halophyte, therefore, Ruppia has both 
hydrophytic and halophytic adaptations. I shall outline first the 
former, taking up in order those modifications that occur in the 
shoot and in the root, and secondly describe the halophytic adaptations. 
HypropaytTic ADAPTATIONS 
A. The Shoot 
1. Gross Morphological Adaptations. 
In its external form and style of branching the stem of Ruppia 
presents a marked contrast to the stem of a typical land plant. 
Since water has such a greater density than air, it becomes no 
longer essential for the plant to have a stout, firm axis capable of 
holding itself erect and supporting numerous branches. Instead we 
find the stems of Ruppia long and slim, and except at the very 
apex, of equal diameter throughout. For the same reason the 
branches are similar, and as long or longer than the principal axis 
from which they arise. Hence the peculiar wide-spreading branch 
system which I have already described—a type impossible in a 
land plant without a copious development of strengthening tissue. 
The leaves of Ruppia, arising from such a weak, slender stem, 
are of enormous length compared with the leaves of an ordinary 
land plant having a main axis of similar diameter. This extreme 
length is again made possible by the greater density of the sur- 
rounding medium. A leaf of similar proportions in a land plant 
would have great difficulty in holding itself out in a plane suitable 
for receiving the rays of light. 
The advantages of this extreiae length seem quite apparent. 
Coupled with the narrowness of the leaf, the effect is just as in 
aquatics with finely divided leaves, such as Batrachium, Cerato- 
phyllum, &c., i. e., to present a large amount of surface to the 
water in proportion to the volume of the leaf. This increase in 
leaf surface is beneficial for several reasons. In all probability much 
of the nutrient mineral solution requisite for metabolism is absorbed 
by water plants directly from the surrounding water. Moreover, 
