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Development of Leaf and Stipular Glands in Coffea arabica
Flora, Bd. 164, S. 11-18 (1975)
Development of Leaf and Stipular Glands in CoJJea arabica J. D.
PATEL
and
M. ZAVERI
(nee Shah)
Department of Botany, Sardar Patel University, Vallabh Vidyanagar, India
Summary The present paper describes the leaf development, the apical growth and the marginal growth in Coffea arabica. The tissue differentiation in the leaf is described and schematically presented. The marginal growth of the leaf blade belongs to the middle submarginal type. Stomata are paracytic. and variations in umber of subsidiary cells are recorded. Trichomes are unicellular and eglandular. The development of stipular gland is traced and it is concluded that in most of the cases formation of the gland takes place by the contribution of the protoderm and subprotoderm cells on the adaxial surface of the stipule. However, in some cases, the basal cells of the gland may be derived from the second subprotodermallayer. Some of the cells of the epithelial layer may show periclinal divisions. The glands lack vascular tissue.
Introduction
Beans of coffee plant provide an important non-alcoholic beverage which enjoys the favour of a large section of the world population, and stands next to tea in its popularity. Its cultivation and economic importance are well studied, but the anatomical aspects have not received satisfactory attention (MARIANI 1908; VAROSSIEAU 1940; METCALFE and CHALK 1950; MOENS 1968; HUXLEY 1969a, 1969b). The work of HUXLEY (1964, 1969a, 1969b) mainly describes various aspects of coffee seed and beans. MOENS (see - 1968) worked out various anatomical, physiological and ecological aspects of Coftea canephora and C. robusta, and only in a few cases C. arabica. Development of leaf and stipulary gland in the species grown in India, C. arabica, has not been carefully worked out previously. With this point in mind the present investigation was taken up. Material and Methods Dr. K. UNNIKRISHANAN of Department of Botany, Calicut University, Kerala, India, fixed the young shoot tips in FAA and 4 % formaldehyde. The pickeld material was transferred to 70 % ethanol and dehydrated through TBA-ethanol series (SASS 1958). Infiltration was done using paraTBA and embedded in tissue prep. Longisections, 8 microns thick, were stained with tannic acid - ferric chloride and counter stained with mordant safranin and fast green combination.
Observations
A. Leaf The leaves borne in opposite pairs have inter-petiolar stipules. The stipules are very small with pointed tip. At the site of leaf initiation the cells of the outermost corpus
= 12
J. D.
PATEL
antll\L
ZAVERI
• Development of Leaf and Stipular Glands
13
layer on the flank of the shoot apex frequently divide peri- and anticlinally. The tunica cells divide only anticlinally. Due to further cell divisions in corpus cells and differential growth of the new derivatives a bulge of leaf buttress is formed, which grows into a leaf primordium. Further growth of the leaf takes place by apical and marginal growth. Apical and marginal growth: Initially the leaf primordium elongates by apical growth. This occurs due to the activity of apical and subapical initials. Apical and subapical initials are established at the tip of the leaf primordium even when it is less than 50 microns in height. The apical and subapical initials are identified by (i) their position, (ii) comparatively large nuclei, (iii) dense cytoplasm, and (iv) thin cell wall. The apical initial divides anticlinally to give rise to protoderm derivatives of the leaf axis (Fig. lA). The derivatives of the apical initial at the margins of the leaf axis act as marginal initials. Whereas, those on the ad- and abaxial sides form the epidermis of the petiole and mid-rib regions of the leaf. The subapical initial divides anticlinvJly to form ad- and abaxial layers, and periclinally to form middle layers of the leaf axis (Fig. lA). The ad- and abaxial derivatives divide anti- and periclinally to increase the number of cell layers (Fig. lA). At the margins of the leaf axis the ad- and abaxial derivatives of the subapical initial act as submarginal initials, whereas those on the ad- and abaxial sides of the leaf axis form cortical tissue of the petiole and ground parenchyma of the mid rib region. The middle derivatives form the mid vein and petiole vasculature. Till the marginal growth initiates, the leaf axis appears oval in transectional view. But, when the leaf axis overtops the height of the shoot apex, two marginal lobes of densely stained cells are seen (in transectional view). Marginal meristem causes the formation of the leaf tlade. The marginal initial (Fig. 1 B) divides only by anticlinal divisions to form ad- and abaxial protoderm of the leaf blade. Below the marginal initial a submarginal initial is present. It divides both anti (Fig. 1 B) and periclinally (Fig. 1 C) to form ad- and abaxial layers, and middle layer of the leaf blade respectively. By further anticlinal and periclinal divisions in ad- and abaxial layers the ad- and abaxial mesophylliayers are formed (Fig. lD), and the middle layer contributes to the formation of the blade vasculature and a few layers of the abaxial mesophyll. In the beginning the adaxial surface above the mid-rib region of the leaf primordium is flat,
Fig. lA-Po Fig. A. Longisection of leaf primordium showing apical and subapical initials. Figs. B-D. Transections, leaf primordium showing marginal growth. Fig. E. Transection, leaf primordium showing activity of adaxial meristem. Fig. F. Transection of leaf blade. Figs. G-M. Ontogeny and structure of stomata. Figs. N-P. Trichome development and structure. (AB, abaxial side; ABE, abaxial epidermis; ABL, abaxial layer; AD, adaxial side; ADE, adaxial epidermis; ADL, adaxial layer; AI, apical initial; GC, guard cell; GMC, guard mother cell; M, meristemoid; MI, marginal initial; ML, middle layer; P, protoderm; SAl, subapical initial; SC, subsidiary cell; 8MI, submarginal initial; VC, vascular cambium.)
~,
2
14 Ground Iissue of mid-vein regIOn and pellole Epidermis of pellOie and mid - vein region (adaxial side) Adaxial protoderm -
Adaxial eptdermis
Adaxial layer Adaxial mesophyll
t
Adaxial merls/em
+
Adaxial m/d- rib bulge Vascular lissue
Al- 111
t
l . SA f ~--~~5!1l- - - - t1lddle
I
layer
A"'xl
m",ophyll
Abaxial (ayer
Abaxial proloderm ~ Abaxial epidermis Epidermis of petiole and mid rib region (abaxial side) Vascular tissue of mid - vein and peliole
Chart I. Schematic representation of the tissue differentiation in the laef of Coffea arabica during the apical and marginal growth activity. but with the development of leaf blade this region appears ~s a bulge. This mid-rib adaxial bulge is formed by the adaxial meristem activity. The subprotodermal cells of the adaxial meristem show frequent periclinal divisions (arrows, Fig. lE), whereas those on the flanks of the adaxial meristem do not show similar divisions. The protodermal cells of the adaxial meristem also show frequent anticlinal divisions (Fig. 1 E). The schematic presentation of the tissue differentiation in the leaf during the apical and marginal growth has been given in Chart 1. The mature leaf lacks spongy and palisade tissue differentiation (Fig. IF). However, the adaxial mesophyll layers (one or two) show large and elongated cells as compared to those of abaxial mesophyll cells, which are small and isodiametric as seen in transectional view (Fig. IF). The epidermal cells of the adaxial surface are vertically elongated whereas those of the abaxial surface are short and small. Stomata and trichomes: With the help of paradermal sections of very young leaves the stomatal ontogeny is studied. A small, lens like, densely stained meristemoid is cut off from a protodermal cell (Fig.1G). It has a prominent nucleus. It divides by an anticlinal wall parallel
Development of Leaf and Stipular Glands
15
to the wall which cuts off the meristemoid from the protodermal cell (Fig. IH) to form a subsidiary cell. A second anticlinal wall, parallel to the first one, is laid down to form a second subsidiary cell (Fig. 1 I). The remaining small cell with dense cytoplasm, acts as a guard mother cell and divides by an anticlinal wall parallel to the first two cell walls to form a pair of guard cells (Fig. IJ), and later a pore is formed in the partition wall between the two guard cells (Fig. lK). Normally, the mature stoma is paracytic (Fig. 1 K). But, sometimes, one of the two subsidiary cells may divide by D wall at right angle to the stomatal length to form two unequal subsidiary cells. Hence, the stoma is anisocytic with three subsidiary cells (Fig. lL). In some other cases, one of the two subsidiary cells contiguous to the guard cells may divide again. But, later, each of the two unequal derivatives may show one or two divisions to lay down cell walls parallel to the longer axis of the guard cells. Thus, seven or more subsidiary cells may be formed (Fig. 1 M). The trichomes are simple, unicellular and eglandular (Figs. 1- 0, P). The cell walls of the trichomes are thick (Fig. IP). Primordial pits are observed in the walls of the trichome. Fig. 1 N shows the surface view of the trichome base in which nucleus is still present. B. Stipular Glands Stipules are covered with a number of large, elongated glands on their adaxial surface. At the site of gland initiation one or two protodermal cells show enlarged size. Their nuclei are larger than the contiguous protodermal cells (Fig. 2 A). Their contents are densely stained. The associated subprotodermal cells have dense cytoplasm, and show peri- and anticlinal divisions (Fig. 2 A). Frequent anticlinal divisions in the protodermal gland initial take place (Fig. 2B), and the subprotodermal cells show enlargement. A small convex bulge of gland is formed due to enlargement of the centrally placed protodermal cells (Fig. 2 B). Further divisions in protodermal as well as subprotodermal derivatives and their subsequent asymmetrical growth bring about the formation of a large bulge (Fig. 2C). The protodermal cells divide only anticlinally, whereas the derivatives of subprotodermal cells divide both peri- and anticlinally. The inner tissue of the gland primordium also shows cell enlargement (Fig. 2C). The differential divisions and growth in the protodermal and inner layers bring about the elongation of the gland primordium (Figs. 2C-F). The gland primordium is eumeristematic in the early stage of its ontogeny (Fig. 2C). However, later, the protodermal layer cells retain their dense cytoplasmic contents, whereas the inner layers gradually show vacuolation in their cells (Figs. 2D-F). The young gland primordium does not show a stalk and a head (Fig. 2D). However, at maturity the basal part of the gland is very narrow, the middle part is broadest and it gradually tapers. Nevertheless, the tip is obtuse (Fig. 2E). The stalk and head differentaiation occurs due to the differential division activity and asymmetrical growth in different parts of the gland primordium (Fig. 2E). The length of the gland, after the middle bulge formation, increases mainly due to the elongation of the middle cells (Figs. 2E, F). The cells at the base and tip regions
16
J. D.
PATEL
and M.
ZAVERI
Fig. 2 A-F. Various developmental stages of stipular gland. (ST, stalk; darts and arrows, as in text.)
Development of Leaf and Stipular Glands
17
elongate less than those in the middle region. The protodermal cells show more periclines during the elongation process of the gland primordium to cope up with the elongation of the middle layers' cells (Fig. 2F). The protodermal cells which are not much elongated at right angle to the inner layers in the beginning, later, form an epithelial layer of the gland. They show radial elongation (Fig. 2F). Usually, the epithelium is uniseriate but at intervals some cells may divide periclinally (at arrows, Fig. 2F). The stipular glands lack vascular tissue (Figs. 2 E, F). The entire gland is developed from the derivatives of protodermal and subprotodermal cells (Fig.2C). However, sometimes, some of the basal cells of the gland are derived from the second subprotodermal layer. In the mature glands the epithelial cells are densely stained and have prominent nuclei, whereas the middle cells are elongated and vacuolated. Some of the cells are devoid of nucleus. Discussion
Coffee shows submarginal type of blade growth. Submarginal type again has been subdivided into adaxial, abaxial and middle submarginal types. Presently investigated species belongs to the last subtype. We have also correlated the apical and marginal growths in the tissue differentiation in the leaf. Members of the family Rubiaceae show rubiaceaous or paracytic type of stomata (METCALFE and CHALK 1950). Apart from this common type, anisocytic, anomocytic, diacytic, and tetracytic stomata are found in the leaf epidermis (PANT 1965; PANT and MEHRA 1965; BAHADUR, RAJAGOPAL and RAMAYYA 1971). Paracytic and anisocytic types are common and some variations of paracytic type have been observed in the presently investigated species. Shagg'y glandular hairs on the stipular surfaces are recorded in the family Rubiaceae as in lsertia (METCALF and CHALK 1950). They secrete mucilaginous material. Such glands have been observed in the adaxial surface of the stipules of coffee plant. HORNER and LERSTEN (1968) have described secretory trichomes in Psychotria bacteriophila which have a multicellular stalk from which radiate many branch cells. The stipular glands in Coffea arabica are different from such secretory trichomes in having a single body with uniseriate (or with periclinal divisions in the cells) epithelial layer enclosing a massive, vacuolated, long cells. The basal part is narrower than the middle one and hence if forms a stalk. The unicellular eglandular trichomes with very thick walls are common in C. arabica as in other species of Rubiaceae (METCALFE and CHALK 1950). Acknowledgements We are thankful to Professor J. J. SHAH and Dr. G. L. SHAH for their encouragement and suggestions throughout this investigation. J. D. PATEL thanks the University Grants Commission for the award of a Sr. Research Fellowship.
References BAHADUR, B., RAJAGOPAL, T., and RA~IAYYA, N.: Studies on the structural and developmental variation and distribution of stomata in the Rubiaceae. Bot. J. Linn. Soc. 64, 295-310 (1971), 2 Flora, Bd. 164
.1:====
,&LJ
18
J. D. PATEL and M. ZWERI, Development of Leaf and Stipular Glands
HORNER, H. T., and LERSTEN, N. R: Development, structure and function of secretory trichomes in Psychotria bactcriophila (Rubiaceae). Am. J. Bot. lili, 1089-1099 (1968). HUXLEY, P. A.: Some factors which can regulate germination and influence viability of coffee seeds. Proc. Int. Seed Test. Assoc. 29, 33-60 (1964). _ Coffee seeds. Kenya Coffee 34, 106-107 (1969 a). _ The structure of the eoffee fruit and "bean". Kenya Coffee 34, 264-266 (1969 b). MARIANI, J.: Les Cafiers. Structure, anatomique de la feuille. Lons-Ie Saunier, L. Declume (1908). METCALFE, C. R, and CHALK, L.: Anatomy of Dicotyledons Vol. II. Clarendon Press, Oxford 1950. MOENS, P.: Investigationes, morfol6gicas, ecol6gicas y fisiologicas sobre dafetes. Turrialba 18, 209-233 (1968). PANT, D. D.: On the ontogeny of stomata and other homologous structures. PlantSc. Sr., Allahabad (India) 1, 1-24 (1965). _ and MEHRA, B.: Ontogeny of stomata in some Rubiaceae. Phytomorphology lli, 300-310 (1965). SASS, J. E.: Botanical Microtechnique. Iowa State College Press, Ames 1958. VAROSSIEAU, W. W.: On the development of the stem and the formation of leaves in Coffea species. Thesis, Brille 1940. Received September 2, 1974. Authors' address: Dr. J. D. PATEL and M. ZAVERI, Department of Botany, Sardar Patel University, Vallabh Vidyanagar, 388120 (India).
Development of Leaf and Stipular Glands in CoJJea arabica J. D.
PATEL
and
M. ZAVERI
(nee Shah)
Department of Botany, Sardar Patel University, Vallabh Vidyanagar, India
Summary The present paper describes the leaf development, the apical growth and the marginal growth in Coffea arabica. The tissue differentiation in the leaf is described and schematically presented. The marginal growth of the leaf blade belongs to the middle submarginal type. Stomata are paracytic. and variations in umber of subsidiary cells are recorded. Trichomes are unicellular and eglandular. The development of stipular gland is traced and it is concluded that in most of the cases formation of the gland takes place by the contribution of the protoderm and subprotoderm cells on the adaxial surface of the stipule. However, in some cases, the basal cells of the gland may be derived from the second subprotodermallayer. Some of the cells of the epithelial layer may show periclinal divisions. The glands lack vascular tissue.
Introduction
Beans of coffee plant provide an important non-alcoholic beverage which enjoys the favour of a large section of the world population, and stands next to tea in its popularity. Its cultivation and economic importance are well studied, but the anatomical aspects have not received satisfactory attention (MARIANI 1908; VAROSSIEAU 1940; METCALFE and CHALK 1950; MOENS 1968; HUXLEY 1969a, 1969b). The work of HUXLEY (1964, 1969a, 1969b) mainly describes various aspects of coffee seed and beans. MOENS (see - 1968) worked out various anatomical, physiological and ecological aspects of Coftea canephora and C. robusta, and only in a few cases C. arabica. Development of leaf and stipulary gland in the species grown in India, C. arabica, has not been carefully worked out previously. With this point in mind the present investigation was taken up. Material and Methods Dr. K. UNNIKRISHANAN of Department of Botany, Calicut University, Kerala, India, fixed the young shoot tips in FAA and 4 % formaldehyde. The pickeld material was transferred to 70 % ethanol and dehydrated through TBA-ethanol series (SASS 1958). Infiltration was done using paraTBA and embedded in tissue prep. Longisections, 8 microns thick, were stained with tannic acid - ferric chloride and counter stained with mordant safranin and fast green combination.
Observations
A. Leaf The leaves borne in opposite pairs have inter-petiolar stipules. The stipules are very small with pointed tip. At the site of leaf initiation the cells of the outermost corpus
= 12
J. D.
PATEL
antll\L
ZAVERI
• Development of Leaf and Stipular Glands
13
layer on the flank of the shoot apex frequently divide peri- and anticlinally. The tunica cells divide only anticlinally. Due to further cell divisions in corpus cells and differential growth of the new derivatives a bulge of leaf buttress is formed, which grows into a leaf primordium. Further growth of the leaf takes place by apical and marginal growth. Apical and marginal growth: Initially the leaf primordium elongates by apical growth. This occurs due to the activity of apical and subapical initials. Apical and subapical initials are established at the tip of the leaf primordium even when it is less than 50 microns in height. The apical and subapical initials are identified by (i) their position, (ii) comparatively large nuclei, (iii) dense cytoplasm, and (iv) thin cell wall. The apical initial divides anticlinally to give rise to protoderm derivatives of the leaf axis (Fig. lA). The derivatives of the apical initial at the margins of the leaf axis act as marginal initials. Whereas, those on the ad- and abaxial sides form the epidermis of the petiole and mid-rib regions of the leaf. The subapical initial divides anticlinvJly to form ad- and abaxial layers, and periclinally to form middle layers of the leaf axis (Fig. lA). The ad- and abaxial derivatives divide anti- and periclinally to increase the number of cell layers (Fig. lA). At the margins of the leaf axis the ad- and abaxial derivatives of the subapical initial act as submarginal initials, whereas those on the ad- and abaxial sides of the leaf axis form cortical tissue of the petiole and ground parenchyma of the mid rib region. The middle derivatives form the mid vein and petiole vasculature. Till the marginal growth initiates, the leaf axis appears oval in transectional view. But, when the leaf axis overtops the height of the shoot apex, two marginal lobes of densely stained cells are seen (in transectional view). Marginal meristem causes the formation of the leaf tlade. The marginal initial (Fig. 1 B) divides only by anticlinal divisions to form ad- and abaxial protoderm of the leaf blade. Below the marginal initial a submarginal initial is present. It divides both anti (Fig. 1 B) and periclinally (Fig. 1 C) to form ad- and abaxial layers, and middle layer of the leaf blade respectively. By further anticlinal and periclinal divisions in ad- and abaxial layers the ad- and abaxial mesophylliayers are formed (Fig. lD), and the middle layer contributes to the formation of the blade vasculature and a few layers of the abaxial mesophyll. In the beginning the adaxial surface above the mid-rib region of the leaf primordium is flat,
Fig. lA-Po Fig. A. Longisection of leaf primordium showing apical and subapical initials. Figs. B-D. Transections, leaf primordium showing marginal growth. Fig. E. Transection, leaf primordium showing activity of adaxial meristem. Fig. F. Transection of leaf blade. Figs. G-M. Ontogeny and structure of stomata. Figs. N-P. Trichome development and structure. (AB, abaxial side; ABE, abaxial epidermis; ABL, abaxial layer; AD, adaxial side; ADE, adaxial epidermis; ADL, adaxial layer; AI, apical initial; GC, guard cell; GMC, guard mother cell; M, meristemoid; MI, marginal initial; ML, middle layer; P, protoderm; SAl, subapical initial; SC, subsidiary cell; 8MI, submarginal initial; VC, vascular cambium.)
~,
2
14 Ground Iissue of mid-vein regIOn and pellole Epidermis of pellOie and mid - vein region (adaxial side) Adaxial protoderm -
Adaxial eptdermis
Adaxial layer Adaxial mesophyll
t
Adaxial merls/em
+
Adaxial m/d- rib bulge Vascular lissue
Al- 111
t
l . SA f ~--~~5!1l- - - - t1lddle
I
layer
A"'xl
m",ophyll
Abaxial (ayer
Abaxial proloderm ~ Abaxial epidermis Epidermis of petiole and mid rib region (abaxial side) Vascular tissue of mid - vein and peliole
Chart I. Schematic representation of the tissue differentiation in the laef of Coffea arabica during the apical and marginal growth activity. but with the development of leaf blade this region appears ~s a bulge. This mid-rib adaxial bulge is formed by the adaxial meristem activity. The subprotodermal cells of the adaxial meristem show frequent periclinal divisions (arrows, Fig. lE), whereas those on the flanks of the adaxial meristem do not show similar divisions. The protodermal cells of the adaxial meristem also show frequent anticlinal divisions (Fig. 1 E). The schematic presentation of the tissue differentiation in the leaf during the apical and marginal growth has been given in Chart 1. The mature leaf lacks spongy and palisade tissue differentiation (Fig. IF). However, the adaxial mesophyll layers (one or two) show large and elongated cells as compared to those of abaxial mesophyll cells, which are small and isodiametric as seen in transectional view (Fig. IF). The epidermal cells of the adaxial surface are vertically elongated whereas those of the abaxial surface are short and small. Stomata and trichomes: With the help of paradermal sections of very young leaves the stomatal ontogeny is studied. A small, lens like, densely stained meristemoid is cut off from a protodermal cell (Fig.1G). It has a prominent nucleus. It divides by an anticlinal wall parallel
Development of Leaf and Stipular Glands
15
to the wall which cuts off the meristemoid from the protodermal cell (Fig. IH) to form a subsidiary cell. A second anticlinal wall, parallel to the first one, is laid down to form a second subsidiary cell (Fig. 1 I). The remaining small cell with dense cytoplasm, acts as a guard mother cell and divides by an anticlinal wall parallel to the first two cell walls to form a pair of guard cells (Fig. IJ), and later a pore is formed in the partition wall between the two guard cells (Fig. lK). Normally, the mature stoma is paracytic (Fig. 1 K). But, sometimes, one of the two subsidiary cells may divide by D wall at right angle to the stomatal length to form two unequal subsidiary cells. Hence, the stoma is anisocytic with three subsidiary cells (Fig. lL). In some other cases, one of the two subsidiary cells contiguous to the guard cells may divide again. But, later, each of the two unequal derivatives may show one or two divisions to lay down cell walls parallel to the longer axis of the guard cells. Thus, seven or more subsidiary cells may be formed (Fig. 1 M). The trichomes are simple, unicellular and eglandular (Figs. 1- 0, P). The cell walls of the trichomes are thick (Fig. IP). Primordial pits are observed in the walls of the trichome. Fig. 1 N shows the surface view of the trichome base in which nucleus is still present. B. Stipular Glands Stipules are covered with a number of large, elongated glands on their adaxial surface. At the site of gland initiation one or two protodermal cells show enlarged size. Their nuclei are larger than the contiguous protodermal cells (Fig. 2 A). Their contents are densely stained. The associated subprotodermal cells have dense cytoplasm, and show peri- and anticlinal divisions (Fig. 2 A). Frequent anticlinal divisions in the protodermal gland initial take place (Fig. 2B), and the subprotodermal cells show enlargement. A small convex bulge of gland is formed due to enlargement of the centrally placed protodermal cells (Fig. 2 B). Further divisions in protodermal as well as subprotodermal derivatives and their subsequent asymmetrical growth bring about the formation of a large bulge (Fig. 2C). The protodermal cells divide only anticlinally, whereas the derivatives of subprotodermal cells divide both peri- and anticlinally. The inner tissue of the gland primordium also shows cell enlargement (Fig. 2C). The differential divisions and growth in the protodermal and inner layers bring about the elongation of the gland primordium (Figs. 2C-F). The gland primordium is eumeristematic in the early stage of its ontogeny (Fig. 2C). However, later, the protodermal layer cells retain their dense cytoplasmic contents, whereas the inner layers gradually show vacuolation in their cells (Figs. 2D-F). The young gland primordium does not show a stalk and a head (Fig. 2D). However, at maturity the basal part of the gland is very narrow, the middle part is broadest and it gradually tapers. Nevertheless, the tip is obtuse (Fig. 2E). The stalk and head differentaiation occurs due to the differential division activity and asymmetrical growth in different parts of the gland primordium (Fig. 2E). The length of the gland, after the middle bulge formation, increases mainly due to the elongation of the middle cells (Figs. 2E, F). The cells at the base and tip regions
16
J. D.
PATEL
and M.
ZAVERI
Fig. 2 A-F. Various developmental stages of stipular gland. (ST, stalk; darts and arrows, as in text.)
Development of Leaf and Stipular Glands
17
elongate less than those in the middle region. The protodermal cells show more periclines during the elongation process of the gland primordium to cope up with the elongation of the middle layers' cells (Fig. 2F). The protodermal cells which are not much elongated at right angle to the inner layers in the beginning, later, form an epithelial layer of the gland. They show radial elongation (Fig. 2F). Usually, the epithelium is uniseriate but at intervals some cells may divide periclinally (at arrows, Fig. 2F). The stipular glands lack vascular tissue (Figs. 2 E, F). The entire gland is developed from the derivatives of protodermal and subprotodermal cells (Fig.2C). However, sometimes, some of the basal cells of the gland are derived from the second subprotodermal layer. In the mature glands the epithelial cells are densely stained and have prominent nuclei, whereas the middle cells are elongated and vacuolated. Some of the cells are devoid of nucleus. Discussion
Coffee shows submarginal type of blade growth. Submarginal type again has been subdivided into adaxial, abaxial and middle submarginal types. Presently investigated species belongs to the last subtype. We have also correlated the apical and marginal growths in the tissue differentiation in the leaf. Members of the family Rubiaceae show rubiaceaous or paracytic type of stomata (METCALFE and CHALK 1950). Apart from this common type, anisocytic, anomocytic, diacytic, and tetracytic stomata are found in the leaf epidermis (PANT 1965; PANT and MEHRA 1965; BAHADUR, RAJAGOPAL and RAMAYYA 1971). Paracytic and anisocytic types are common and some variations of paracytic type have been observed in the presently investigated species. Shagg'y glandular hairs on the stipular surfaces are recorded in the family Rubiaceae as in lsertia (METCALF and CHALK 1950). They secrete mucilaginous material. Such glands have been observed in the adaxial surface of the stipules of coffee plant. HORNER and LERSTEN (1968) have described secretory trichomes in Psychotria bacteriophila which have a multicellular stalk from which radiate many branch cells. The stipular glands in Coffea arabica are different from such secretory trichomes in having a single body with uniseriate (or with periclinal divisions in the cells) epithelial layer enclosing a massive, vacuolated, long cells. The basal part is narrower than the middle one and hence if forms a stalk. The unicellular eglandular trichomes with very thick walls are common in C. arabica as in other species of Rubiaceae (METCALFE and CHALK 1950). Acknowledgements We are thankful to Professor J. J. SHAH and Dr. G. L. SHAH for their encouragement and suggestions throughout this investigation. J. D. PATEL thanks the University Grants Commission for the award of a Sr. Research Fellowship.
References BAHADUR, B., RAJAGOPAL, T., and RA~IAYYA, N.: Studies on the structural and developmental variation and distribution of stomata in the Rubiaceae. Bot. J. Linn. Soc. 64, 295-310 (1971), 2 Flora, Bd. 164
.1:====
,&LJ
18
J. D. PATEL and M. ZWERI, Development of Leaf and Stipular Glands
HORNER, H. T., and LERSTEN, N. R: Development, structure and function of secretory trichomes in Psychotria bactcriophila (Rubiaceae). Am. J. Bot. lili, 1089-1099 (1968). HUXLEY, P. A.: Some factors which can regulate germination and influence viability of coffee seeds. Proc. Int. Seed Test. Assoc. 29, 33-60 (1964). _ Coffee seeds. Kenya Coffee 34, 106-107 (1969 a). _ The structure of the eoffee fruit and "bean". Kenya Coffee 34, 264-266 (1969 b). MARIANI, J.: Les Cafiers. Structure, anatomique de la feuille. Lons-Ie Saunier, L. Declume (1908). METCALFE, C. R, and CHALK, L.: Anatomy of Dicotyledons Vol. II. Clarendon Press, Oxford 1950. MOENS, P.: Investigationes, morfol6gicas, ecol6gicas y fisiologicas sobre dafetes. Turrialba 18, 209-233 (1968). PANT, D. D.: On the ontogeny of stomata and other homologous structures. PlantSc. Sr., Allahabad (India) 1, 1-24 (1965). _ and MEHRA, B.: Ontogeny of stomata in some Rubiaceae. Phytomorphology lli, 300-310 (1965). SASS, J. E.: Botanical Microtechnique. Iowa State College Press, Ames 1958. VAROSSIEAU, W. W.: On the development of the stem and the formation of leaves in Coffea species. Thesis, Brille 1940. Received September 2, 1974. Authors' address: Dr. J. D. PATEL and M. ZAVERI, Department of Botany, Sardar Patel University, Vallabh Vidyanagar, 388120 (India).