Nor are strand-plants however ordinary xerophytic psammophytes. Psammophytes are as a rule deep rooted, and draw on deep-lying water for their supply. These strand -plants do not. Their roots do not grow deep, and in Spinifex at least the root-hairs are, as we have seen, close to the surface and depend apparently on water close to the surface of the ground. This water would, we have seen, he fresh. A certain amount of salt must be blown in from the sea as spray and this would be leached though the surface layers by the next shower of rain down to a certain depth. Perhaps this accounts for the formation of an exodermis and the absence of root-hairs on the lower roots of Spinifex squarrosus.
Finally there is another condition different from that of either a desert or sand-field. The air blown across from the sea is damp. It is never dry by the sea, except when the land breeze blows strongly it is damp close to the water. The strand-plants therefore are xerophytic in the sense of having to depend on very little fresh water, but in regard to the water lost by evaporation from the leaves have much less to fear than even mesophytic inland plants. They are surrounded by air as damp as that round a lake. They are not halophytes. They are not xerophytes in the ordinary sense, but subject to the peculiar condition of a shortage of water available to the roots, yet without liability to extensive loss from the leaves. Perhaps their chief physiological characteristic is therefore the ability to carry on metabolism with a minimum of water passing through the system.
As regards the xerophytism of strand-plants, Kearney (5) came to similar conclusion after analysis of the salt-content of the soil. He found that seashore sand contains less salt than some cultivated soils. Kearney insists on the xerophytic character of plants as being due to dry winds and dry sand. But a distinctly moist air seems in Madras to be the rule near the sea.
Literature Cited.
(1) Olssoh-Seffer. New Pbytologist VIII (1909), p. 38.
(2) Price, B. New Phytologist X (1911), p. 328 et seq.
(3) Schimper, A. F. W. S.B.K. Preuss, Akad, Wiss., 1890, pp. 1045-1062 extr. in J. R.M.S. 1891, p. 214. Plant Geography, p. 184.
(4) Warming E. (Ecology— Eng. Ed. (1909), p. 227.
(5) Kearney. T. H. Bot. Gazette, XXXVII (1904), p. 424.
