Article Contentsp. 145p. 146p. 147p. 148p. 149p. 150p. 151p. 152p. 153p. 154p. 155Issue Table of ContentsBiotropica, Vol. 9, No. 3 (Sep., 1977), pp. 145-216Front Matter [pp. ]Studies on the Growth of Red Mangrove (Rhizophora mangle L.) 4. The Adult Root System [pp. 145-155]Rolled-Leaf Hispine Beetles (Chrysomelidae) and their Zingiberales Host Plants in Middle America [pp. 156-169]Correlations of Inflorescence, Flower Structure, and Floral Anatomy with Pollination in Some Palms [pp. 170-190]Effect of Light, Temperature, and Flooding on Seed Germination of the Neotropical Panicum laxum Sw. [pp. 191-194]Structure of Mangrove Forests in Florida, Puerto Rico, México, and Costa Rica[pp. 195-212]Solitary and Group Foraging: Two Flower-Visiting Patterns of the Lesser Spear-Nosed Bat Phyllostomus discolor [pp. 213-215]NotesOptimal Foraging Theory Used to Deduce the Energy Available in the Environment [pp. 216]Back Matter [pp. ]Studies on the Growth of Red Mangrove (Rhizophora mangle L.) 4. The Adult Root SystemAuthor(s): A. M. Gill and P. B. TomlinsonSource: Biotropica, Vol. 9, No. 3 (Sep., 1977), pp. 145-155Published by: The Association for Tropical Biology and ConservationStable URL: http://www.jstor.org/stable/2387877 .Accessed: 30/08/2011 15:38Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jspJSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected] Association for Tropical Biology and Conservation is collaborating with JSTOR to digitize, preserve andextend access to Biotropica.http://www.jstor.orgStudies on the Growth of Red Mangrove (Rhizophora mangle L.) 4. The Adult Root System A. M. Gill CSIRO Division of Plant Industry, P.O. Box 1600, Canberra, A.C.T. 2601, Australia and P. B. Tomlinson Harvard Forest, Harvard University, Petersham, Massachusetts 01366, U.S.A. ABSTRACT Aerial roots in Rhizophora arise from stems, branches, and secondarily thickened, anchored, aerial roots, but only after injury from unanchored aerial roots. Lateral subterranean roots are abundantly developed upon penetration of a mud substrate whereupon the histology of the root undergoes marked and abrupt changes so that chlorophyll is no longer de- veloped, trichosclereids no longer differentiate, tannin cells become few, the cortex becomes markedly lacunose, and the sequence of protoxylem differentiation changes. Root systems developed in contrasting environments like water, sand, or mud provide evidence as to the relative importance of light and air in affecting anatomical differentiation. The over- all morphology of the root system is discussed in relation to its likely function in aeration of subterranean parts. WE HAVE OUTLINED briefly the general features of the root system of Rhizophora mangle (Gill and Tomlinson 1969), and we now amplify that prelim- inary statement. In another article in this same ser- ies (Gill and Tomlinson 1971a) the distinctive me- thod of growth of aerial roots of red mangrove, which leads to distinctive anatomical features, was described. This present article completes the account of the de- velopment of the root system by describing distal an- chorage of aerial roots, the overall establishment of the characteristic looping, above-ground root system, changes in the anatomy of roots as they penetrate the substrate, and also discusses the likely physiology of roots in relation to the distribution of gas space within them. An attempt is made to relate these fea- tures to the general ecology of the Rhizophora root system in differing environments. Since the aerial roots of Rhizophora are one of the most striking features of the genus, they have oc- casioned frequent comment, as early as 305 B.C. by Theophrastus (Bowman 1917). Scientific investiga- tions in more recent times have included those of Warming (1883), Karsten (1891), Schenck (1889), and Boergesen and Paulsen (1900). Most interest has centered on the likely function of aerial roots in the aeration of the attached subterranean roots which are typically anchored in anaerobic soils (Jost 1887, Karsten 1891). Direct demonstration of this role in aeration remains to be done, as indeed it does with the root systems of most trees. In fact, the aerating function has remained difficult to demonstrate con- vincingly (e.g., Kramer et al. 1952 for Taxodium). Evidence is largely circumstantial, but the most re- cent comprehensive investigation by Scholander et al. (1955), using Rhizophora and Avicennia, seems con- clusive. Mention should be made, however, of the interpretation by Troll and Dragendorff (1931) of the root system of Sonneratia caseolaris as a mech- anism for adjusting to soil accretion and not as an aerating system. In our present study we are concerned more with the dynamic morphology of the root system than with its function, but we emphasize that a detailed knowledge of structure must precede any discussion of physiology. Further, the root system of Rhizophora provides one among many examples of aerial root systems in tropical plants in which there are strik- ing morphogenetic responses to abruptly changing environments (Gill and Tomlinson 1975). Our pres- ent-study includes little experimental work; we have largely relied upon natural variation of roots in dif- ferent substrates to provide evidence for causal re- sponses. This information has provided insight into the ecological adaptability of the Rhizophora root sys- tem, since so much previous description has referred to an invariate root environment which is tide-washed and has a soft, anaerobic substrate. In South Florida, at least, Rhizophora habitats are often varied, and the response of root systems to this variation must be considered along with aeration. BIOTROPICA 9(3) 145-155 1977 145METHODS Investigations were conducted largely in the vicinity of Fairchild Tropical Garden, Miami, Florida, dur- ing the period 1968-1971, the locality already re- ported on in earlier papers of this series (Gill and Tomlinson 1969, 1971a, 1971b). Additional obser- vations were made on a wider variety of root habitats elsewhere on the shores of Biscayne Bay and in the Everglades