PER CENT CALCIUM CARBONATE 1.0 | 100.0 -— L L_ Oo 10.0 100 0 —io.0 , — — p Oo 5 Oo oO oO Oo m —~} ~ -— O E z mn €ao 10.0-— = ° &F | a a = > 3 | a -o SEAWATER oO = z aw A 8 , | °nT z oO = c = » Ag _ lo 90 Cc Oo 0 = 2 "n > O Co oO 4 oO b = 3 4 épb <I 1.0 -— ° — rn 0.1 a = o — b— x | oO on mb = = Pp + m —~ 0. | 0.001 a | Lilet 0.01 1 Et tTiity 0.1 | L SEN Sa A CALCIUM(gm/gm) Fig. 12.—The variation in the [UJ/[Ca] ratio with the degree of calcification of the algae cified of the organisms is in direct contrast to the discrimination found for strontium in various freshwater algae.8) It would be particularly desirable to extend this study to include the other Group II elements, Magnesium, strontium, and barium in order to ascertain whether the behavior found in the case of radium is peculiar to that element. Generally, those organisms which have a high [Sr]/[Ca] ratio also have high [Ra]/[Ca] ratios.2® In addition it would be interesting to include in this more extended study samples of the family Cryptonemiales, the coralline red algae, which even though they are tropical orga- nisms, deposit calcium carbonate as the stable rhombohedral calcite. In the argonitic Halimeda opuntia the concentration of strontium carbonate is 1.3%,‘2)) while in the caleitic red algae its concen- tration is only 0.35%.'?2) The reverse situation is true for the concentration of magnesium.(2) This behavior is the result purely of ionic size. Substitution of larger ions for calcium in the calcite lattice is limited by the steric factors of a close packedlattice. REFERENCES 1. Bowen, H. J. M. Trace Elements tn Biochemistry. Academic Press, London, 1966, pp. 68-73. 2. Mauchline, J. and Templeton, W. L. Oceaneg. Mar. Biol. Ann. Rev. 2, 229 (1964). 3. Vinogradov, A. P. Sears Found. Mar. Res., Memoir No. 2 (1953). 4. Lucas, H. F. Rev. Sct. Instr. 28, 680 (1957). 5. Edgington, D. N. Int. J. Appl. Rad. Isotopes 18, 11 (1967). 6. Lucas, H. F. and Edgington, D. N. Modern Trends in Activation Analysis, Ed. DeVoe, J. R. National Bureau of Standards Special Publ. No. 312 (1969), p. 1207. 7. Analytical Methods for Atomic Absorption Spectrophotometry Perkin-Elmer, Norwalk, Conn., 1968. 8. Lindner, R. C. Plant Physiol. 19, 76 (1944). 9. Morris, I. An Introduction to the Algae, Hutchinson & Co., London, 1967, p. 10. 10. Lewin, J. C. Silicification. Physiology and Biochemistry of Algae, Ed. R. A. Lavin. Academic Press, New York 1962.