Proc. Indian Acad. Sci., Vol. 84 B, No. 5, 1976, pp. 173-179

Dermal morphology of 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 , 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- 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 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 . 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 , 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 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 . 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 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

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÷ . ;k" ..-,.'-.-: ~: .'.>~.;k ~. ,: :. ~::.,.~.: , "':-'~~:~2": .:: .,. ~ ..:.:

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.~:,~ ...... "': ;.~, .'-~-, .... ~i

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Figures 1-8. 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). On three sides, the guard cells are surrounded by neighbouring epidermal cells.

In mature leaves of V. planifolia, the guard cells show a strong ten- deney to degenerate. 80~ of the stomata in the older leaves have either only one guard cell or only the stomatal aperture and subsidiary cells left after degeneration (figures 8, 15). Varying degrees of degeneration could also be observed in many eases.

4. DISCUSSION

The significance of dermal morphology, particularly stomatal mor- phology, irt taxonomic and phyletic studies, seems to be well accepted in recent years. Each major group of monocotyledons is reported to be eharaeterised by a definite stomatal type. 1 However, the inconsistency of stomatal types in some groups and taxa has led some workers ~ to regard stomata as a taxonomic character of doubtful significance and reliability. A diversity of stomatal types, occurring on the same surface, has been reported in many dicotyledons.°-1~ In monoeotyledons this appears to be not as prevalent as in dicotyledons, being reported in a few cases like Pandanales and Spathiflorae 6 and Dioscorea where as marry as six different types of stomata are reported within a single genus. 7 Despite this, many workers consider that the pro dominant stomatal type in a taxon can still be a valuable tool in elucidating phylogeny and relationships, even in such cases where there is much variability in stomatal morphology2

The occurrence of more than one type of stomata in Vanilla and the fact that they are predominantly of the para-mesoperigenous type, in con- trast to the aperigenous type prew.lent in the rest of the reported cases in Orchidaceae, apparently lend support to the view that stomatal morphology constitutes a weak taxonomic criterion. But the predominance of para- mesoperigenous stomata in both the species of Vanilla indicates that this type may be characteristic of the taxon. The stomata ort the scale-leaves of II. wightii and 16~o of the stomata in V. planifolia are aperigenous as in the rest of the reported cases of Orehidaeeae. The aperigenous types ar~ DERMAL MORPHOLOGY IN Vanilla 179

considered to be more advanced than the rest of the types. 1 The genus Vanilla, with its poorly organised pollinial apparatus, is considered to be one of the primitive members of Orchidaceae. The prevalence of a compa- ratively less advanced type of stomata in this genus is in keeping with its primitive status in the family.

It is interesting in this connection that the genus Curculigo of Hypoxi- daceae, which occupies a key position in the evolution of Orchidaceae from the primitive Liliaceous stock, also has para-mesoperigenous stomata. 7 This app~.rently points to the fact that the aperigenous stomata found in the advanced Orchidaceae are probably derived from the para-mesoperi genous type.

The widespread degeneration of guard cells in mature leaves V. plani- folia is interesting, in view of the fact that this species is an introduced plan and has long been under cultivation.

REFERENCES

1. Stebbins, G. L. and Khush, G. S., Am. J. Bet. 48 51 (1961). 2. Paliwal, G. S., Acta. Bet. Need. 18 (5) 654 (1969). 3. Inamdar, J.A., Curr. Sci. 37 24 (1968). 4. Santapau, H. and Henry, A. N., A Dictionary of Flowering Plants of India p. 180 (CSIR, New Delhi) (1973).

5. Fryns-Claessens, E. and Van Cotthem, W., Bot. Rev. 39 71 (1973). 6. Pant, D. D. and Kidwai, P., Senckenb. Biol. 47 309 (1966). 7. Shah, G. L. and Gopal, B. V., Ann. Bot. 36 1005 (1972). 8. Shah, G. L. and Gopal, B. V., Ann. Bot. 34 737 (1970). 9. Inamdar, J. A., Curr. ScL 36 443 (1967). 10. Paliwal, G. S., PhytomorphoL 15(1) 50 (1965). 11. Pant, D. D. and Gupta, K. L., J. Linn. Soc. (Bot.) 59 265 (1966). 12. Pant, D. D. and Mehra, B., Flora 155 179 (1964).