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Syst. 17: 273 sloughing in the littoral zone coralline alga, Spongiles yendoi - 303. (Fos1ie) Chamberlain (Corallinales, Rhodophycota). Phycologia STENECK, RS., HACKER, S.D. & DETHIER, M.N. 1991. Mecha­ 32: 143 - 150. nisms of competitive dominance between crustose coralline algae: KEATS, D.W., WILTON, P. & MANEVELDT, G. in press. Ecologi­ an herbivore-mediated competitive reversal. Ecology 72: 938 - cal significance of deep-layer sloughing in the eulittoral zone 950. Epidermal structure, organographic distribution and ontogeny of stomata in vegetative and floral organs of Stenoglottis fimbriata (Orchidaceae) J. Samuelt and A.B. Bhat* t Department of Education, Umtata, Transkei, Republic of South Africa • Department of Botany, University of Transkei, Private Bag XI, Urntata, Transkei, Republic of South Africa Received 10 August 1993; revised 8 December 1993 The epidermal structure and ontogeny of stomata in all vegetative and floral organs of Stenoglottis fimbriata were investigated. Epidermal cells are polygonal or isobilateral. The leaf sheath, inner whorl of the perianth, column and tuber are astomatic. Other organs investigated are heterostomatic and of anomocytic origin. The ontogeny of stomata is perigenous and attention has been paid to various aspects of development. Abnormalities such as degeneration of guard cells, superimposed and juxtaposed contiguous stomata, persistent stomatal cell contiguous with normal stoma, and stoma with persistent intervening wall, were observed. Stomatal and epidermal cell fre­ quency, and stomatal index are also tabulated. These characters are of taxonomic importance for the family Orchidaceae. Die bou van die epidermis en die ontogenie van huidmondjies is by aile vegetatiewe en blomorgane van Stano­ glottis fimbriata ondersoek. Epidermisselle is poligonaal of isobilateraal. Die blaarskede, binneste periantkrans, suit en knol is sonder huidmondjies. Ander organe wat ondersoek is, is heterostomaties van anomositiese oarsprong. Die ontgenie van huidmondjies is perigeen en daar is genoeg aandag aan die verskillende aspekte van ontwikke­ ling gegee. Abnormaliteite 5005 degenerasie van sluitselle, oarheenliggende en teenaanliggende aangrensende huidmondjies, blywende tussenliggende wand, is waargeneem. Die groatste huidmondjies onder blomplante is oak by die spesie aangeteken. Huidmondjie-indeks word getabuleer. Hierdie kenmerke is van groat taksonomiese belang by die familie Orchidaceae. Keywords: Epidermal structure, ontogeny, organographic distribution, Stenoglottis fimbriata, stomata . • To whom correspondence should be addressed. Introduction tropical orchids. Williams (1979), Rasmussen (1981) and Stenoglottis Jimbriata Lind!. is one of the many orchid species Singh (1981) studied the diversity of stomatal developments in reported from the coastal zones of Transkei (Stewart et al. Orchidaceae. Recently Das & Paria (1992) investigated the 1982). Considerable work has been done on vessel structure of stomatal structure of some Indian orchids with reference to Orchidaceae by Cheadle & Kosakai (1982), but very little taxonomy. This investigation was undertaken to investigate the attention has been paid to the epidermal structure of orchids. Rutter & Willmer (1979) studied the epidermis of Paphiopedi­ epidermal structure, organographic distribution, structure and lum spp. and Hew et al. (1980) have reported on the distri­ ontogeny of stomata in Stenoglottis Jimbriata with reference to bution and frequency of stomata in flowers and leaves of a few its taxonomic significance. 114 S.-Afr.Tydskr.Plantk., 1994, 60(2) Material and Methods guard cells and are found oriented along the long axis of the Plants of Stenog/otlis jimbriaJa in blossom were collected from stomata (Figures 2, 5 & 6). The anticlinal cell walls are Port St. Johns, Langeni forest, Umtata and the Unitra campus, straight or slightly arched in leaves, peduncle, sheathing leaf Transkei, South Africa. Epidermal peels were taken from vegeta­ base and at the basal part of the bract, but they are arched or tive and reproductive parts, stained in Delafield's haematoxylin sinuous in the peri anth , ovary wall, column, tuber and the and mounted in glycerine. Epidermal layers were also taken by upper part of the bract (Figures 3 & 5). The maximum length gently heating the specimens in dilute nitric acid. The peels were of the epidermal cell observed is 399 ~m on the adaxial side thoroughly washed in distilled water and neutralized in dilute of the sheathing leaf base, while the minimum length of the sodium hydroxide solution for better staining. The technique of epidermal cell is 78 ~m found in the column. The maximum Bhat & Etejere (1985) was also used to take imprints of the width is 162 ~m on the adaxial surface of the leaf while a epidermis. Observations were made by using a binocular micro­ minimum of 44 ~m is found on the adaxial side of the scope Leitz Lab 11. Mean values of thirty observations of each perianth. The highest and the lowest epidermal cell frequency organ were taken to calculate the stomatal frequency, stomatal per mm2 is 219 and 56 on the adaxial surface of the bract and index, size of the stomata in f.Lm, frequency and size of epidermal on the abaxial surface of the leaf, respectively. cells. The results are given in Table 1. All the observations are supported by the diagrams, drawn by using camera lucida (Figures Trichomes and papillae 1 - 20). The terminology used to explain the stomatal types is Unicellular, uniseriate trichomes with blunt tips are observed from Metcalfe & Chalk (1950) and Van Cotthem (1970). on almost every alternate epidermal cell on the peduncle (Figure 14). Water vesicles are commonly observed on the Results adaxial side of the lamina, bract and perianth (Figures 4, 5, 12 Epidermis & 13). Vesicular hairs are also observed on the margins of the The leaves are hypostomatic while the bract and the outer perianth lobes (Figure 20). whorl of the perianth are amphistomatic. The peduncle and ovary wall are stomatic, while the tuber, sheathing leaf base, Stomata inner whorl of the perianth and the column are astomatic. The The stomata are exceptionally large in size. The plant organs epidermal cells of the abaxial surface of the leaf are typically which are stomatic show anomocytic (Figure 4), staurocytic hexagonal, or polygonal and oriented along the long axis of the (Figure 7), tetracytic (Figures 6 & 12) and actinocytic (Figure organ (Figure 2), whereas the epidermal cells of the sheathing 19) stomata. The anomocytic stomata of Metcalfe & Chalk leaf base, peduncle and the base of the bract possess elongated (1950) are the predominant type observed. Anomocytic stoma­ polygonal epidermal cells (Figures 9 & 14). Extra-floral ta with three neighbouring cells are frequently present in all the nectaries are frequently observed on the adaxial epidermal organs investigated (Figures 8 & 15). In all cases the stomata layer of the lamina. These nectaries are predominantly situated are oriented along the long axis of the organ. Chloroplasts are at the point where the cross walls of the adjacent cells meet clearly observed in the guard cells of the vegetative parts, but (Figure 13). Almost every epidermal cell of the adaxial side of in the guard cells of the floral parts some colourless bodies are the leaf, bract and perianth is dome-shaped due to the presence noticed. The walls of the ventral side of the guard cells are of a water vesicle (Figures 4, 5 & 12). Bundles of calcium strongly thickened around the stomatal pores (Figures 2, 8 & oxalate crystals are observed in the epidermal cells of the 12). In many cases a persistent intervening