Studies in Halophytes: III. Salinity Factors in the Growth of Australian Saltbushes

occur in small quantities relative to the monovalent ions. Phosphorus and nitrogen levels (ca. 0.15 and 3% respectively) are high in comparison with other native plants. The soils supporting A triplex vary tremendously in the mineral constituents mentioned above, but in spite of these variations the plants accumulate ions to approximately the same extent: For example, the extreme values recorded for chloride in the soils are 19 and 9250 ppm., whereas the extreme values for chloride in the leaves are 9.6 and 13.6% of the dry weight. Plants growing in these two extreme habitats appear the same as far as leaf form and size and general healthiness are concerned. The ratio of sodium to potassium is of special interest. This ratio varies tremendously from soil to soil (extreme values: 2.1 to 131). In the plants, however, the ratio does not show such a wide variation (extreme values: 1.9 to 8.5) from which it may be inferred that the plants prefer potassium to sodium. Further investigations under laboratory conditions on the importance of sodium, potassium and chlorine, and on the interaction f sodium and potassium, in the growth of Atriplex are being carried out.