418 SHARITZ AND LUVALL 



induced environmental disturbances occur intermittently, plant and 

 animal species that have already undergone natural selection to 

 withstand fluctuating conditions with low predictability may be of 

 major importance in maintaining ecosystem structure. 



ACKNOWLEDGMENTS 



We thank J. H. Thorp and D. H. Nelson for their ideas and 

 development of related studies, S. A. Wineriter for aid in maintaining 

 the temperature chambers, K. A. VandenBosch for assistance in 

 counting the plants, J. E. Pinder III for statistical advice and analysis, 

 and J. B. Coleman for drafting the figure. The manuscript was 

 reviewed by E. H. Liu and J. W. Gibbons. Research was performed 

 under contract EY-76-C-09-0819 between the U. S. Department of 

 Energy and the University of Georgia. 



REFERENCES 



Ashby, E., and T. A. Oxley, 1935, The Interaction of Factors in the Growth of 



Lemna. VI. An Analysis of the Influence of Light Intensity and Temperature 



on the Assimilation Rate and the Rate of Frond Multiplication, Atrn. Bot. 



(London), XLIX: 309-336. 

 , E. Wangermann, and E. J. Winter, 1949, Studies in the Morphogenesis of 



Leaves. III. Preliminary Observations on Vegetative Growth in Lemna minor, 



NewPhytoL, 48: 374-381. 

 , and E. Wangermann, 1951, Studies in the Morphogenesis of Leaves. VII. 



Part II. Correlative Effects of Fronds in Lemna minor. New PhytoL, 50: 



200-209. 

 Christiansen, M. E., and J. D. Costlow, Jr., 1975, The Effect of Salinity and 



Cyclic Temperature on Larval Development of the Mud-Crab Rhithro- 



panopeus harrisii (Brachyura: Xanthidae) Reared in the Laboratory, Mar. 



Biol., 32: 215-221. 

 Clatworthy, J. N., and J. L. Harper, 1962, The Comparative Biology of Closely 



Related Species Living in the Same Area. V. Inter- and Intraspecific 



Interference Within Cultures of Lemna spp. and Salvinia natans, J. Exp. Bot., 



13: 307-324. 

 Claus, W. D., 1972, Lifespan and Budding Potential of Lemna as a Function of 



Age of the Parent, iVeu;P/i>'fo/,, 71: 1081-1095. 

 Costlow, J. D., and C. G. Bookhout, 1971, The Effect of Cyclic Temperatures 



on Larval Development in the Mud-Crab Rhithropanopeus harrisii, in Fourth 



European Marine Biology Symposium, D.J. Crisp (Ed.), pp. 211-220, 



Cambridge University Press, London. 

 Dickson, H., 1938, The Occurrence of Long and Short Cycles in Growth 



Measurements of Lemna minor, Ann. Bot. (London), II: 97-106. 

 Grainger, J. N. R., 1959, The Effect of Constant and Varying Temperatures on 



the Developing Eggs of Rana temporaria L., Zool. Anz., 163: 267-277. 



