Proc. Indian Acad. Sci., Vol. 84 B, No. 5, 1976, pp. 173-179 Dermal morphology of Vanilla planifolia Andr. and V. wightii Lindl. B. K. NAYAR, F.A.Sc., RAJENDRA RAI AND P. VATSALA Department of Botany, Calicut University, Kerala 673635 MS received 8 April 1976 ABSTRACT In contrast to other Orchidaceae, the stomata in Va;ziila planifolia and V. wightii, are predominantly of the para-mesoperigenous type but the meristemoid is squarish as in other members of the family. 16~S of the stomata in V. planifclia and the stomata on the scale-leaves of V. wightii are of the aperigenous type; in V. planifolia, a few stomata (8~) are anisomesogenous (meristemoid triangular) and others (2~o) hemipara-mesop~rigenous. In V. Mghtii subsidiary cells of the para- mesoperigenous cauline stomata divide secondarily to form 5-7 subsidiary cells. Stomata are abundant on the stem of V. wightii (stomatal index-3.4) but sparse in V. planifolia (index-0.57). There is a progressive increase in stomatal index from base to apex of the leaf of V. planifolia. About 80~; of the the stomata in mature leaves of V. planifolia degenerate, as leaves get older.The epidermis is devoid of trichom~s in both species. In V. planifc.lia, each epidermal cell has a large crystal included in it. It is suggested that the stomatal types in Vanilla indicate the relationship of Orchidaceae to Hypoxidaceae, through Curculigo, which also has para- mesoperigenous stomata. 1. INTRODUCTION DIFFERENT Natural Orders, especially of the Monocotyledons, are reported to possess characteristic stomatal types and the aperigenous type is the rule in Orchidaceae. 1, ~ Though a large and widespread family, the Orehidaceae is little known from the point of view of dermal morphology. However, recorded observations, including the study of the terrestrial Habenaria marginata Coleb. by lnamdar, 3 confirm that stomata of the aperigenous type are characteristic of the family. Vanilla is a large, pan- tropical, terrestrial, climbing genus of about 90 species, of which four are reported to occur in India? V. planifolia Andr. is a native of tropical 173 B4--Nov. 76 174 B. K. NAYAR, et aL America and is cultivated to a limited extent in the Western Ghats for its fruits, which are the source of commercial vanillin. V. wightii Lindl. is wild in the southern regions of Western Ghats. During a comprehensive study of V. planifolia ~.nd V. wightii, certzin interesting aspects of their dermal morphology were observed. These are reported in the present communication. 2. MATERIALSAND METHODS Material of V. planifolia was collected from an experimental plantation of over a hundred 3-year-old plants in the Calieut University campus. V. wightii was collected in the wild from Tirunelveli District and grown in the Botanical Garden of the University. Young leaves were fixed in Carnoy's fluid for 24 hr. Epidermal peelings were taken with a razor bla.de, stained with Delafield's haematoxylin and mounted in aqueous glyce- rine. All observations on stomatal ontogeny are based on these prepara- tions. For observations on mature stomata, peelings were taken from the stem as well as mature leaves without prior fixation. The stomatal index was c.~.lculated from the apical, middle and basal regions of the leaf and from adult stem. All illustrations included in the text are camera-lucida tracings. The terminology used is that of Fryns-Claessens and Van Cotthem. 5 3. OBSERVATIONS Both V. planiJblia and V. wightii possess succulent, cylindrical, deep green and glossy stems. The leaves are l~.rge and fleshy in V. planifolia and undeveloped and scale-like in V. wightii. Dermal appendages are totally absent on the stem and leaves in both species. The cells of the epidermis of the stem and leaves in V. planifolia are small, thick-walled, sparsely chloro- phyllous and radi~.lly compressed, arranged in irregular longitudinal rows parallel to the long axis of the organ. They are polygonal in surface view and have straight anticlinal walls. The cells are 20-35 tz across along the long axis of the stem and leaf, 30-44/z broad and 20-30/~ tall. The cells of the epidermis of the If. wightii stem are similar to those of V. planifolia, but those of the scale-leaves are markedly elongated along the long axis of the leaf (45-200 /~ x 40-95/~). Both upper and lower epidermis in V. planifolia are contiguous at the margin of the leaf. The cells at the extreme margin possess thicker walls than other epidermal cells. Four or five rows of mesophyll cells in this region are also thick w~.lled and are devoid of chlorophyll, so that the leaf-margin appears cartilagenous. Prominent pit-connections are found on the radial and inner walls of all epidermal cells (figure 8). At maturity all epidermal cells on the stem and leaf of V. planifolia possess characteristic DERMAL MORPHOLOGY IN Vanilla 175 ~~"k~ '::" ~' ~ ......... ....•..!:~,, ~, ~,,~..,~,.~,.,..,.. ~.,'~-.:Z.~,~. :.~I~-..~:~ 'xo~. ~ :.~.-, ~,~ ...,.. • .. ~~:° .;.~ i, v ..,.'~. -~"~ .'"~.."--------------~4." ~ • ÷ . ;k" ..-,.'-.-: ~: .'.>~.;k ~. ,: :. ~::.,.~.: , "':-'~~:~2": .:: .,. ~ ..:.: ;-:.~,, . ~?.-'-~ ..... t:. •':-, -~ ~.~ ~~ 5 .~:,~ ..... "': ;.~, .'-~-, .... ~i ~r~,, ,-.-.'~:?~ Figures 1-8. Vanilla planifolia Andr. 1. Lower epidermis showing stomatal distribution. 2--4. Stages in the development of para-mesoperigenous stoma, showing the square meristemoid, two-celled, three-celled and four-celled stages. 5. The first division of the meristemoid in the formation of hemipara-mesoperigenous stoma. 6. The triangular meristemoid which gives rise to the aniso-mesogenous stoma. 7. T.S. of the stoma. 8. Enlarged view of the lower epidermis showing pit-connections, one degenerated stoma with only the stomatal aperture left and the thin- walled subsidiary ceils. 176 B.K. NAYAR et aL transparent crystals included in special crystal-sacs (figure 8). Usually a single large crystal is found per cell, but occasionally two or even three are observed. The crystals of lower foliar epidermis are cubical (6-12 /~ across) while those of upper epidermis are elongated (6-10 /z x 15-20/~). Crystals are absent in V. wightii. Leaves in both species are hypostomatie. In V. planifolia there is a progressive increase in stomatal frequency from the base to the apex of the leaf, the stomatal index being 3-6 towards the base, 4"6 in the middle and 5.5 towards the apex. The stomatal index of the stem is 0" 57 in this species. In K wightii stomata occur regularly on the stem and the index is 3-4. In both species stomata are arranged parallel to the long axis of the stem or leaf and are flush with the surface of the epidermis (figures 1, 7). The guard cells are kidney-shaped, measuring 30-35/z in length and 15-20/z in width. The characteristic crystals found in the epidermis of V. planifolia are absent in guard cells and subsidiary cells. The subsidiary cells have thinner walls than the surrounding epidermal cells (figure 8). The predominant type of stomata in both species is the para-mesoperi- genous type (tetracytic). 73~o of the stomata in V. planifolia and almost all on the stem of K wightii are of this type. There are four subsidiary cells, two parallel to the guard cells and derived from the meristemoid and are hence mesogenes and the other two polar in position and derived from neighbouring cells and are hence perigenes (figure 9). As in Habenaria marginata a the meristemoid is squarish (figure 2). It undergoes two successive divisions, both in the vertical plane, cutting off two subsidiary cells towards either side and a guard cell mother cell in between (figure 3). The latter by another vertical division gives rise to the two guard cells (figure 4). Meanwhile, the epidermal cell on each polar end, adjascent to the guard cells, undergoes a tangential division each, producing a peri- genous subsidiary cell at each end (figure 4). Occasionally, only one of the polar cells undergoes division. In V. wightii, very frequently, the four subsidiary cells undergo further division either by radial walls, giving rise to 6-8 subsidiary cells, all touching the guard cells or by tangential walls, producing double rows of subsidiary cells (figures 16, 17). 16~ of the stomata in V. planifolia and the stomata of the scale-leaves of V. wightii are aperigenous (anomocytic). Subsidiary cells are absent and the guard cells on all sides are surrounded by neighbouring epidermal cells (figures I0, 13). The meristemoid directly functions as the guard cell mother cell and divides equally by a vertical wall to give rise to two guard cells. In V. planifolia, 8~ of the total stomatal complement are of the aniso- mesogenous type (anisocytic) and 2~ of the hemipara-mesogenous type, DERMAL MORPHOLOGY IN Vanilla 177 Figures 9-17. 9-12. Para-raesoperigenous, aperigenous, hemipara-mesoperigenousandaniso- mesogenous stomata on the lower epidermis of the leaf Vanilla planifolia. 13-14. Stomata on the scale-leaf of Vanilla wightii Lindl. 15. Stomata with one guard cell seen in mature leaf of 1I. planifolia. 16 and 17. Stomata on the stem F. wightii showing increase in numberofsubsidiarycells, byradialdivisionsartdtangential divisions, respectively. 178 B.K. I~IAYAR et aL In the former, the guard cells are surrounded by three mesogenous subsi- diary cells, of which one is smaller than the other two (figure 12). The meristemoid is triangular and trilabrate (figure 6). It undergoes three successive divisions by anticlinal walls to produce the three subsidiary cells. The first formed is the largest and the last the smallest. The hemipara- mesoperigenous type has only one subsidiary cell lying parallel to one of the guard cells (figure 11). The meristemoid undergoes one division in the vertical plane; one of the daughter cells functions as the guard cell mother cell and the other becomes the subsidiary cell (figures 5, 6).