The Morphology of Ruppia Maritima. 121 
the root in its very young stages. It may be here again noted 
(cf. p. 107) that possibly the soil or the water, containing common 
salt in solution, would injure the very young root if not thus protected. 
2. Internal Structural Adaptations. 
a. Air Spaces. 
The root cortex, as is the case in the shoot, shows many inter- 
cellular spaces, but much smaller. These, however, are often made 
larger by the collapsing of the cells. The function of these air 
spaces may probably be explained in the same way as in the shoot 
(5119); 
b. Reduction of the Vascular System. 
The vascular bundle of the root, of essentially the same structure 
as that of the stem, admits of the same interpretation, as regards 
the reduction of its elements, as in the stem. Especially significant 
is the reduction in this case, however, since the root is properly 
the absorbing organ of an ordinary plant, and as such should possess 
at all events a well developed vascular system. The absence of such 
a one here is the most conclusive proof of the comparative small 
amount of absorption carried on by the root system. 
In this connection the presence of thin-walled tracheal cells without 
thickenings, still intact in the xylem area of the bundle, is inter- 
esting in comparison with the axial canal caused by their dissolution 
in the stem. Their presence may indicate a need for them in the 
root, and therefore some degree of absorption by this organ. 
Hatopyytric ADAPTATIONS 
A. General 
It was pointed out by Schimper (1890, p. 1047, and 1891, pp. 25 ff.) 
that any considerable amount of salt in the cell sap is detrimental 
to the plant, and that here we have the probable cause of the 
characteristic halophytic modifications, which aim, therefore, at a 
lessening of the transpiration current. To this Warming (1902, p. 309, 
310) replied that even if transpiration were diminished to a very low 
degree, slowly but surely an amount of salt would be collected in 
the plant which would eventually prove fatal. On the other hand, 
Warming saw better logidfin ancther idea of Schimper (1890), which 
has become the widely accepted view at the present time—namely, 
that the protective contrivances against strong transpiration are 
necessary in halophytes, because absorption of water from a salt 
solution is slow and difficult. 
