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 ifnot 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 ceUs. The function of these air 

 spaces may probably be explained in the same way as in the shoot 

 (p. 119J. 



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. 



Halophytic 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 logic in another idea of Schimper (1890), which 

 has become the widely accepted view at the present time — namety, 

 that the protective contrivances against strong transpiration are 

 necessar}' in halophytes, because absorption of water from a salt 

 solution is slow and difficult. 



