COLLECTION AND STORAGE OF WATER. 277 



ished surface exhibited by the larger grass-like plants and by the 

 evergreen leaves of Quercus and Ilex. This last peculiarity is, how- 

 ever, doubtless primarily induced by the necessity for protection 

 against loss of water. 



ADAPTATIONS FOR PROTECTING THE SUPPLY OF WATER. 



Strand plants upon Ocracoke Island, unlike deser^ plants, are not to 

 any noteworthy extent equipped with special apparatus for collecting or 

 for storing water, if we except the development of water-storage tissue 

 in several of the salt-marsh species. The obvious reason is the absence 

 of a period of drought, there being at all times a relatively high per- 

 centage of water in the air and the soil. On the other hand, both 

 maritime and desert vegetations are characterized by certain pecul- 

 iarities of structure, especially of the leaves, which are usually 

 denominated xerophytic, albeit these are less strikingly developed in 

 strand plants than in those which inhabit deserts. Such common 

 points of resemblance are, as is well known, due to a common necessity 

 for protection against excessive loss of water by transpiration from 

 the leaves, and this despite the abundant supply of water in the 

 environment of strand plants. 



In the case of salt-marsh vegetation it is chiefly the presence of a com- 

 paratively high percentage of sodium chlorid in the soil water which 

 necessitates a xerophytic structure. Just how this salt reacts upon 

 the life processes of plants and what the precise mode is by which 

 plants protect themselves against its injurious effects are much mooted 

 questions. 1 



'Contejean (Geogr.bot. , pp. 71, 94) holds that salt is harmful to most plants; that 

 it is not indispensable even to strand plants, and that the latter are confined to an 

 otherwise unfavorable habitat merely by their inability to compete in the struggle 

 for existence with the salt-shunning species of nonsaline soils. That this view is 

 only partially correct is suggested by the known tendency of halophilous (salt- 

 loving) species to take up greater quantities of sodium chlorid, even when grown 

 in nonsaline soils, than do plants which are not halophilous. 



Schimper (Strand-flora, pp. 35, 26) attributes to the accumulation of sodium chlo- 

 rid in the green tissue an injurious effect upon assimilation, particularly upon the 

 production of starch and sugar. More recently (Pfianzengeogr., p, 100) he modi- 

 fies this view, but still emphasizes the importance of a chemical action of the salt 

 upon metabolism, the synthesis of proteids being the process chiefly affected. 



In order to reduce this deleterious action to a minimum, the accumulation of 

 sodium chlorid in the tissues must be as far as possible retarded. This is accom- 

 plished, according to Schimper' s theory, by diminishing root osmosis and hence 

 the volume of the ascending column of water holding the chlorid in solution, 

 this end being secured by means of certain modifications of leaf structure that 

 reduce the volume of transpired water. Besides this chemical effect, Schimper 

 also admits a direct physical influence which the presence of common salt in the 

 soil exerts upon the process of osmosis. As Sachs (Landw. Versuchsst. vol. 1, p. 

 22-i) demonstrated by experiment, the roots of ordinary plants take up with diffi- 

 ctdty water which holds in solution sodium chlorid las well as other salts nota- 

 bly calcium sulphate), a difficulty that of course increases with the concentration 



