CONCERNING THE MORPHOLOGY OF ISOLATED PLANT CUTICLES

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1 New Phytol. (1969) 68, CONCERNING THE MORPHOLOGY OF ISOLATED PLANT CUTICLES BY R. T. LANGE Institut fur Biologie der Universitdt Tubingen {Received 28 August 1968) SUMMARY The morphological basis of cuticle analysis is discussed. A resume is provided of the categories of microrelief occurring on the inner and outer surfaces of isolated plant cuticles. This is illustrated with photographs obtained by electron-scanning microscopy. Some existing interpretations of cuticle morphology are called into question. INTRODUCTION Jurasky (1934, 1935a, b), Krausel and Weyland (1950) and Harris (1956) have discussed cuticle analysis, the palaeobotanical technique of obtaining taxonomically useful information by observing cuticular membranes isolated from fossil plants. The isolated cuticle conveys, in the microrelief of its surfaces, two kinds of taxonomically useful information about the parent plant: (a) information about the epidermis which secreted the cuticle and (b) information intrinsic to the cuticle itself. Emergent epidermal morphologies such as cutinized trichomes are obviously indicated, as are the outlines of submerged cutinized structures like stomatal pores and glandular pits. Further, the inner face of the cuticle bears a contact mould of the epidermal face. This mould usually indicates the outlines of non-emergent epidermal cells. In addition, cuticle surfaces often possess folds, wrinkles and rugosities which, while not necessarily indicative of epidermal cell arrangements, may yet characterize the parent plant. Optical sections through the cuticle yield plane images derived from these morphological characters, hence transmitted-light microscopy serves for cuticle analysis. For general purposes, it serves very well. It fails, however, to permit unequivocal interpretation of three-dimension detail in much of the morphology giving rise to such plane images. This creates problems. For instance grooves, folds and wrinkles, on either surface, can appear simply as striae in transmitted-light images. Present terminology usually refers to the striae, not to the morphological characters themselves or to the surfaces on which they occur, and it therefore needs refinement. More seriously, topographies are sometimes ascribed to the wrong surface, or optical artefacts are interpreted as morphological realities. Interference microscopy and electron microscopy offer solutions. Both have been applied to cuticles (e.g. Leyton and Armitage, 1968; Linskens, 1966; Sitte and Rennier, 1963; Juniper, 1959; Bollinger, 1959) but with reference to natural outer surfaces replete with encrusting waxes. Cleaned outer surfaces such as confront the palaeobotanist, and the important inner surface with its epidermal mould and independent relief, have been neglected. N N.P. 423

2 424 R- T. LANGE Observations by electron-scanning microscopy, such as those described here, illustrate the microrelief on both inner and outer surfaces as these extend between gross structures such as stomata and trichomes, and can be used to support a brief resume of the categories of such microrelief. Certain existing interpretations are then called into question. TOPOGRAPHY OF OUTER SURFACES Topographies are of two kinds differing in relationships and scale. First, the outer surface may exhibit systems of concavities and convexities of the same scale and in the pattern of underlying epidermal cells. Plate i, Nos. 1-4, illustrates varieties and degrees of such relief: grooves (No. i), concavities (No. 2), convexities (No. 3) and sacs (No. 4). The variety encountered is great, but the basic relationship to underlying cell arrangement is common to all. Secondly the outer surface may exhibit independent microrelief. Typically this is on a much smaller scale than the first-order relief, ranging from smooth through degrees and varieties of granulation (e.g. fine grain. No. 5; coarse grain, No. 6) to warting, for example (No. 7). Its variety then extends in scale and nature to creasing and heavy folding (No. 8), obscuring any first-order relief. TOPOGRAPHY OF INNER SURFACES As with outer surfaces, topography is of two kinds, differing in relationships and scale. Generally, the inner relief is much more pronounced and contrasted than is the outer relief. First, inner surfaces may exhibit ribbing, corresponding to inward penetrations of the cuticular matrix between anticlinal walls of abutting epidermal cells, where these walls diverge and curve into the periclinal plane. Surprisingly, ribs rarely possess the keeled or V-shaped section usual in illustrations from leaf transverse sections. At one extreme, ribs may be absent, or rudimentary (No. 9). At the other extreme, ribs with most complicated transverse sections can project as a complex'honeycomb' on the inner face of the cuticle (No. 10). Of the many variations between these extremes, hemicylindrical (No. 11) and U-sectioned types (No. 12) are common. Secondly, the inner surface may exhibit independent microrelief. In the interstices of the rib-mesh, surfaces may be for example smooth (No. 13) or granular (No. 14). Ribs themselves may be smooth (No. 13) or rough (No. 14), stratified (No. 14), broken (No. 15), extensively interrupted (No. 14) or otherwise distinguished. Cuticles may also exhibit wrinkle-patterns as in an otherwise-undetectable surface film. Wrinkles may be fine (No. 11) or may describe a mesh of polygons (No. 13) or other figures across the major relief of ribs. DISCUSSION Observations of identical cuticles by both electron-scanning and transmitted-light microscopy indicate the difficulties of interpreting morphology by light microscopy alone. Such difficulties may have led to misinterpretations. For example the concept and exposition of an external 'wallartig' condition and the idea that the middle lamella is expressed in isolated cuticle morphology ('... Kontaktlinie sichtbar... nicht sichtbar'), as advanced by the 'Cuticulae' working group of the Commission Internationale de

3 THE NEW PHYTOLOGIST, 68, 2 PLATE I 13 P " ^ R. T. LANGE MOi^PffOLOGF OF ISOLATED PLANT CUTICLES "^^Z^^'O (facing page.^24

4 Morphology of isolated plant cuticles 425 Microflore du Paleozoique (1964), require re-examination. Transmitted-light microscopy, which serves admirably for inspecting gross structure, supports only limited interpretation of surface detail. Interpretation of surface detail requires direct observations on the surfaces as such. A two-stage system of terminology and description is required; i.e. a terminology based on transmitted-light observations (e.g. 'striae'), qualified by description based on surface observations (e.g. '... the result of parallel folds on the external surface'). ACKNOWLEDGMENTS Grateful acknowledgment is made to the Alexander von Humboldt Stiftung, to the University of Adelaide, to Professor K. Magdefrau and Professor A. Seilacher, and to Mr H. Scholtz. REFERENCES ARBEITSGRUPPE 'CUTICULAE' DER C.I.M.P. (1964). Entwurf flir einheitliche diagnostische Beschreibung von Kutikulen Fortschr. Geol. Rheinld Westf., 12, 11. BOLLINGER, R. (1959). Entwicklung und Struktur der Epidermisaussenwand bei einigen Angiospermblattern. y. ultrastruct. Res., 3, 105. HARRIS, T. M. (1956). Die fossile Pflanzenkutikula. Endeavour, 15, 210. JUNIPER, B. E. (1959). The surfaces of plants. Endeavour, 18, 20. JuRASKY, K. A. (1934). Kutikular-Analyse. I. Biologia gen., io (2), 383. JuRASKY, K. A. (i93sa). Kutikular-Analyse. II. Biologia gen., 11 (i), 227. JuRASKY, K. A. (1935b). Kutikular-Analyse. III. Biologia gen., 11 (2), i. KRAUSEL, R. & WEYLAND, H. (1950). Kritische Untersuchungen zur Kutikular-Analyse tertiarer Blatter. Palaeontographica, 91 (B), 7. LEYTON, L. & ABMITAGE, I. P. (1968). Cuticle structure and water relations of the needles oi Pinus radiata (D. Don.). New PhytoL, 67, 31. LiNSKENS, H. F. (1966). Das Relief der Blattoberflache. Planta, 68, i. SiTTE, P. & RENNIER, R. (1963). Untersuchungen an Cuticularen Zellwandschichten. Planta, 60, 19. EXPLANATION OF PLATE I Numbers in parentheses refer to Adelaide Herbarium (AD) and Waite Institute Arboretum (WI), South Australia, voucher specimens, from which were obtained the leaf cuticles illustrated in Nos No. I. Hakea salicifolia (Vent.) B. L. Burt (AD ), outer face, x 575. No. 2. Dysoxylon fasceranum Benth. (WI 782), inner face, x 570. No. 3. Acacia melanoxylon R. Br. (AD 28183), outer face, x 635. No. 4. Persoonia falcata R. Br. (AD ), outer face, x 260. No. 5. Dissiliaria tricomis Benth. (AD ), outer face, x No. 6. Pittosporum undiilatum Vent. (WI 1005), outer face, x No. 7. Aloe succotrina Lam. (Bot. Gdn, Tubingen), outer face, x 235. No. 8. Rhodamnia trinerva (Sm.) Blume (AD 967'i33o6), outer face, x 635. No. 9. Pittosporum undulatum Vent. (WI 1005), inner face, x 570. No. 10. Dissiliaria tricomis Benth. (AD ), inner face, x 560. No. II. Dysoxylon fasceranum Benth. (WI 782), inner face, x 570. No. 12. Aloe succotrina Lam. (Bot. Gdn, Tubingen), inner face, x 235. No. 13. Stenocarpus sinuatus Endl. (WI 230), inner face, X No. 14. Aloe succotrina Lam. (Bot. Gdn, Tubingen), inner face, x No. 15. Persoonia falcata R. Br. (AD ), inner face, x 1230.

THE STRUCTURE OF THE CUTICLE IN RELATION TO CUTICULAR TRANSPIRATION IN LEAVES OF THE HALOPHYTE SUAEDA MARITIMA (L.) DUM.

New Phytol. (1983) 94, 125-131 12 5 THE STRUCTURE OF THE CUTICLE IN RELATION TO CUTICULAR TRANSPIRATION IN LEAVES OF THE HALOPHYTE SUAEDA MARITIMA (L.) DUM. BY M. A. HAJIBAGHERI, J. L. HALL* AND T. J,