122 A. H. Graves, 
On account of this difficulty in water absorption, then, one finds 
exhibited in land halophytes many water-storing devices and typical 
xerophytic methods of diminishing transpiration. 
The water halophytes, on the contrary, especially the submerged 
aquatics, such as Ruppia, Zostera, Phyllospadix, &c.—members of 
the Enalid hydrophytic society of Warming (1902, p. 156) as above 
noted—evince none of these modifications. The hydrophytic adap- 
tations already described for Ruppia show how closely this plant 
resembles a typical submerged fresh water hydrophyte. Although 
surrounded by salt water to a much greater extent than land 
halophytes, yet it shows none of the characteristic xerophytic mod- 
ifications which are associated with land halophytes in general. 
The explanation of this may be based on the fact that trans- 
piration, as such, does not appear in Ruppia. The comparatively 
small amount of water absorbed by the roots, the absence of any 
openings in the leaf through which water could pass, such as 
Sauvageau (1891, II, pp. 127 ff.) has described for Zostera, Phyllos- 
padix, Halodule and Potamogeton; moreover, the fact that the 
epidermal cells of the leaf, with the exception of the secretion cells, 
are all photosynthetic and absorb solutions from the outside into 
the interior, indicate the giving off of a very small amount of water, 
if any from the leaves. Waste gases, however, can easily pass out 
through the cell walls in solution. On account of these conditions, 
structures adapted to the retention of a supply of water and 
reduction of transpiration, are unnecessary, and we accordingly find 
an absolute lack of such halophytic adaptations in Ruppia. 
B. The Adaptation to a Salt Water Environment 
In one particular, however, Ruppia shows a distinct halophytic 
adaptation. This is exhibited in its power to withstand the plas- 
molytic action of salt water. Ganong (1903) has found that the 
root hairs of certain land halophytes possess specific abilities to 
resist plasmolysis in various solutions of sea water, showing in this 
way a greater or less halophytic adaptation. He says (1903, 
pp. 358, 354), “I found a close correspondence between the halo- 
philism of a plant and the power of its root hairs to resist plas- 
molysis. This power has of course been gradually acquired, but 
what its physical basis is I do not know though we shall probably 
find that substances osmotically equivalent to the salt of the sea 
water have been formed in the sap of the hairs.” 
But Ruppia, and all of the allied salt water genera, such as 
Zostera, Phyllospadix, &c., show an even greater adaptation than 
