Studies in the Family Saxifragaceae* Vii

STUDIES IN THE FAMILY SAXIFRAGACEAE* VII. Floral Morphology and Development of Gametophytes in Ribes L.

BY N. P. SAXENA** (School of Plant Morphology, Meerut College, Meerut, India) Received August 25, 1969

(Communicated by Professor V. Purl, r.A.SC.)

ABSTRACT The flowers are pentamerous. The staminal bundles arise con- jointly with the sepal medians and the petal bundle with adjacent sepal laterals. The dorsal bundles of the carpel remain indistinct although. The ambers in Rioes are dithecors and show a glandular tapetum. The pollen grains are dimorphic and are shed at bieelled stage. The ovules are anatropol, s, bitegmic and crassinucellate. The development of embryo sac conforms to Polygonum type. Two cases of twin tetrads of megaspores (False Polyembryony) have also been reported. Transfer of the genuo into a new family cf its own is not favoured.

INTRODUCTION THE genus Ribes has long been a subject of interest for morphologists. The contributions made by Dahlgren (1930), Mauritzon (1933) on post-fertili- zation changes; Yen (1936), Morf (1950) on the anatomy of fruit and flower; and Zielinski (1953) on cytology are notable. The present communication, however, deals with the anatomy of the flower in three species and the structure and development of gametophytes in two species of Ribes. The flower-buds and flowers of R. missouriense Nutt. and R. cynosbati Linn. were collected by Dr. Y. S. Murty, from Chicago (U.S.A.) and those of R. roezlii Regel. by Prof. H. F. Copeland from California (U.S.A.). Following usual method of dehydration and embedding, the material was sectioned at 10-12 t~ and stained with safranin and fast green combination which gave satisfactory results.

* Research Contribution No. 96 from the School of Plant Morphology, Meerut. ** Present address: Department of Botany, D.N. College, Meerut. B5 213 214 N.P. SAXENA

OBSERVATIONS Gross morphology.--Three species of the genus, viz., R. missouriense, R. cynosbati and R. roezlii examined are prickly or glabrous shrubs with alternate, exstipulate leaves and epigynous, pentamerous flowers. The floral tube is more or less prolonged beyond the ovary. In R. missouriense and R. roezlii it is nearly cylindric while in R. cynosbati is companulate. The gynoecium is one-celled and bears two parietal placentae. In R. roezlii the ovary is covered with small spinous outgrowths. The pedicel is covered with two types of hair: (i) simple single-celled, pointed and (ii) glandular, as characteristic of other genera of Saxifragaceae, with a multi-celled, multi-seriate stalk and a glandular, globose head (Figs. 11-12). Floral anatomy.--Besides some minor differences the three species resemble closely in their vascular anatomy, as such only R. missouriense is described in detail and differences for the others are only noted. The vascular cylinder of the pedicel breaks up into a ring of ten col- lateral strands at the base of the receptacle (Figs. 2-3). Out of these two opposite strands give off one branch each inwards (Fig. 3-5). These branches are concentric in R. missouriense (Figs. 6). In R. cynosbati, however, they are inversely oriented in the beginning but later on become concentric. They are the ventral strands. R. roezlii appears to be somewhat different. In this case the vascular supply of the pedicel consists of a ring of several vascular bundles which branch and anastomose and then reorganise into six strands and two opposite groups of vascular tissue (Figs. 13-14). Each group of vascular tissue gives off two strands outwards during its upward course and then itself becomes the ventral strand (Fig. 15). A locule makes its appearance in the centre and gradually widens. The massive placentae appear opposite those ventral strands and bear ovules in many vertical rows. The ventral strands furnish several traces for the ovules borne on the respective placentae (Fig. 5). The ten peripheral strands referred to above send several traces which supply the ovary wall and in their inward course they branch profusely (Figs. 6-7). A few of them supply the disc which, at a subsequent level, lines the floral tube as well as encircles the stylar base (Figs. 1, 8, 16). Nec- taries have been described from a number of genera and families occurring in relation with different floral organs (see Fahn, 1953). q-hese floral nectaries have diverse morphological nature (see Puri, 1951 ; Eames, 1961). In a passing reference Parcival (1965) pointed out that the nectaries in peri- ~nous Rosaceae and Saxifragaceae are receptacular. Since the supply of Studies in the Family Saxifragaceae--VII 215

I I mr~ I @ 13 ~!4 15 Fios. 1-16 the disc is received from the peripheral strands at different levels and that the carpellary dorsals do not become differentiated from the rest of the vascular tissue, the nature of the disc traces cannot be judged correctly. Thereafter, the remaining traces arrange themselves into a ri,g and come ~loser to the ventral strands (Fil~. 8). Each ventral ~trand divides into 1;.W9 216 N, P. SAXENA normally oriented ventral bundles at a level when the styles become distinct (Figs. 8-9). The aforesaid ring of vascular bundles extend into the style but disappears in the lower stylar region. Each stigma receives two ventral bundles belonging to same carpel (Figs. 9-10). The ten strands of the floral tube alternately behave as SmSt and SIP (Figs. 8-10). The single petal bundle as well as the lateral bundles of the sepal divide after entering the organ. In a cross-section a sepal shows 6-9 bundles and a petal 3-4 bundles (Fig. 10). The filaments separate from the floral tube at the level of the stigmas. In R. cynosbati and R. roezlii the separation of these organs takes place at a comparatively higher level. Development of gametophytes.--The development of g~metophytes has been studied in R. missouriense and R. cynosbati. As the two species of the genus resemble closely with each other, therefore, only the former has been described in detail. Microgametogenesis and male gametophyte.--The anther wall as in other plants consists of an outer cutinised epidermis, a single-layered endothecium, 2 to 3 (R. missouriense) or 1 to 2 (R. cynosbati) middle layers and a tapetum (Figs. 17, 19). The cells of epidermis are tenniferous of places and those of middle layers greatly compressed and as such are tangentially elongated. The tapetum is glandular in nature. The tapetal cells are rectangular and become binucleate at maturity. The endothecium develops a characteristic fibrous thickening at the time of dehiscence (Figs. 18-19). The dehiscence of the anther takes place by the disappearance of the septum between two pollen chambers of the anther lobe accompanied by the formation of a slit in the region of stomial groove (Fig. 2). The micro- spores of R. cynosbati are much bigger in size than those of R. missouriense (Figs. 20-23). The nucleus of a uninucleate microspore divides and this division is accompanied by wall formation. As such a small biconvex gene- rative and a big vegetative cell is formed (Figs. 20-21). In R. cynosbati the resulting nuclei are of almost equal size (Figs. 22-23) and as in other Saxi- fragaceae (see Webb, 1902; Pace, 1912; Raghavan and Srinivasan, 1942) they are shed at bicelled stage. However, in Saxifraga diversifolia the pollen is shed at 3-celled stage (Saxena, 1964). Due to lack of young material the various stages of microsporogenesis could not be seen. Megasporogenesis and female gametophyte.--The ovules are anatropous, bitegmic and crassinucellate (Fig. 43). The earliest stags seen in the develop- mQnt is a megaspore mother cell having three parietal cells above (Fi~. 25), Studies in the Family Saxifragaceae--VIl 217

18 22 23 ®z,@ ~~0,5mt~j

O,Imr~ ' 2 4 6 27 25 l! - !s (:~ /L-

O~Smm i

~, -..' ---d

39 1 44

FIGS. 17--48

A few vertical divisions occur in the parietal cells (Fig. 26). The megaspore mother cell then divides to form a dyad (Fig. 27). The upper dyad iS comparatively smaller than the lower one. The dyad in turn divides tQ 218 N.P. SAXENA form a linear or T-shaped tetrad (Figs. 28-30, 32-34). An isobilateral tetrad has also been recorded in R. missouriense (Fig. 31). Although the four megaspores are not arranged in typical isobilateral manner, both the arrangement appears to be more close to isobilateral pattern. A similar tetrad of megaspores has been reported by author (Saxena, 1964 b) in Parnassia nubicola. So far there appears to be no record of such a type of tetrad from this family. Two cases of twin tetrads of megaspores amounting to false polyembryony have also been recorded in R. missouriense. On ore of them the two tetrads lie one above the other whereas in the other case they lie side by side (Figs. 45-49). In both the cases the tetrads are lirear. In all probability the second tetrad in R. missouriense originated from a second megaspore. The author has also reported the occurrence of twin embryo sacs in Saxifraga diversifolia and Bergenia ciliata (Saxena, I963, 1969b). Out of four, generally the lowest megaspore functions. It divides thrice, in the usual manner and the resulting eight nuclei organise into a Polygonum type of embryo sac (Figs. 35-39, 40-44). The egg apparatus in B. cynosbati shows a "filiform apparatus " and the synergids are spurred (Fig. 44). Similar structures have also been observed in Saxifraga hieracifolia Ly Wiggins (1959). Systematic consideration.--While most of the workers has preferred to put it in Saxifragaceae the genus, Ribes, has occasionally been assigned to a family of its own (Lindley, 1853; Lemaout and Decaisne, 1876; Hut- chinson, 1926, 1959; Rydberg, 1932; Tippo, 1938; Porter, 1959, etc.). Melchior (1964) while revising Engler's "Syllabus der pflanzenfamillien " raised the status of Ribes from tribe to sub-family. The present observations reveal that besides its bushy habit and herry fruit, Ribes differs frcm Saxi- fraginae only in having indistinct dorsal and pentoporate or zono-aperturale pollen grains (Saxena, 1969 a). Tippo (1938), on the basis of wood anatomy, places Grossulariaceae between Hydrangeaceae and Escalloniaceae. Hew far the establishment of a new family on this ground in justified, is a matter of individual interpretation and does not warrant any discussion here. In the view of present author, a striking similarity in the floral anatcmy or Ribes with Heuchera (Saxifraginae) (SmSt and SIP pattern) and also its bitegmic crassinucellate ovule, it is more appropriate to plAce the genus in the family Saxifragaceae near Saxifraginae rather than raising and putting it along with Hydrangeoideae and Escallonoideae.

ACKNOWLEDGEMENTS The author acknowledges his gratitude to Dr. Y. S. Murty for his guidance and many helpful suggestions and to Professor V. Puri for ~aking Studies in the Family Saxifragaeeae--VII 219 keen interest in the work and also critically going through the manuscript. He is also thankful to Dr. R. Shiam for helping in various ways and to the Ministry of Education for the financial assistance.

REFERENCES

Dahlgren, K. V. O. .. " Zur embryologie der Saxifragoideen," Svensk. Bot. Tidskr., 1930, 24, 429-48. Eames, A. J. .. l~lorphology of At~giosperms, New YGrk, 1961. Fahn, A. .. "The topography of thc nectary in the flowers and its phylogenetical trend," Phytomorphology, 1953, 3, 424-26. Hutchinson, J. .. The Families of Flowering Plar, ts, Vol. I, Dicotyledons, London, 19 26. The Families of Flowering Plants, Vol. I, Oxford, 1959. Lemaout, E. and Decaisne, J... A General System of Botany--Descriptive and Analytical, London, 1876. Lindley, J. .. The Vegetable Kingdom, London, 1853. Mauritzon, J. .. "Studien fiber die embryologie der Familien Crassulaccae und Saxifragaceae," Diss., Univ. Lurid., 1933. Melchior, H. .. A Engler's Syllabus der Pflananzen-familien, II, Band, Berlin, 1964. Morf, E. .. "Vergleichende-morphologische Untersuchungen am Gyno- sceum des Saxifragaceen," Ber. Schweiz. Bot. Ges., 1950, 60, 516-90. Pace, L. .. "Parnassia and some allied genera," Bot. Gaz., 1912, 54, 306-29• Parcival, M. S. .. Floral Biology, Oxford, 1965. Porter, C. L. .. Taxonomy of Flowering Plants, London, 1959. Purl, V. •. "The role of floral anatomy in the solution of morphological problems," Bot. Rev., 1951, 17, 471-553. "Placentation in angiosperms," Ibid., 1952, 18, 603-51. Raghavan, T. S. and Srinivasan .. "A contribution to the life-history of Vailha viscosa Roxb. and Vahlia otdenlandioides Roxb.," Proc. lnd. Acad. Sci., 1942, 15 B, 83-105. Rydberg, P. A, .. Flora of the Prairies and Plains of CentraLNorth Amer&a, New York, 1932. Saxena, N. P. .. "Twin embryo sacs in Saxifraga diversifolia Wall,." Scl. & Cult., 1963, 29, 614-15. .. "Studies in the family Saxifragaceae. I. A. contribution to the Morphology and embryology of Saxifraga diverst- folia Wall.," Proc. Ind. Acad. Sci., 1964, 60, 36--51. .. "Pollen grains in some species of Ribes L." Palynol. Bull. 1969 a, 4, 94-96. 220 N. P. SAXENA

Saxena. N. P. .. "Studies in the family Saxifragaceae. IV. A contribution to the Embryology ofBergenia ciliata (Royle) Raizada," Proc. Ind. Acad. Sci., 1969 b, 70, 103-10. Tippo, O. .. "Comparative anatomy of the Moraceae and their pre- sumed allies," Bot. Gaz., 1938, 100, 1-99. Webb, J. E. .. "A morphological study of the flower and embryo of Spiraea," Ibid., 1902, 33, 451-60. Wiggins, I. L. .. "Development of the ovule and megagametophyte in Saxi- fraga hieracifolia," Amer. Jour. Bot., 1959, 46, 692-97. Yen, T. K. .. "Floral development and vascular anatomy of the fruit of Ribes aureum," Bot. Gaz., 1936, 98, 105-20. Zielinski, Q. B. .. "Chromosome numbers and meiotic studies in Ribes," Ibid., 1953, 1141 265-74.

EXPLANATION OF FIGURES

FIGS. 1-16. Fig. 1. Semi-diagrammatic longitudinal section of the flower of Ribes missouriense showing the course of vascular supply to various floral organs. Figs. 2-10. Serial cross- sections of the flower of the same from base upwards. Figs. 11-12. Magnified unicellular and glandular hairs of R. cynosbati. Figs. 13-16. Serial transections of the flower of R. roezlii. (N, disc; P, petal bundle; SI, sepal lateral; SIp, sepal lateral-petal strand; Sm, sepal median; SmSt, sepal median-stamen strand; St, stamen bundle; Vs, ventral strand.)

FIGS. 17-46. Figs. 17-18. Portions of the anther wall of R. missouriense magnified showing binucleate tapetum in one and fibrous thickening in the other. Fig. 19. A portion of the anther wall of R. cynosbati showing binudeate tapetum and fibrous thickening in the endothecium. Figs. 20-21 and 22-23. Single and bicelled pollen grains of R. missouriense and R. cynosbati respectively. Fig. 24. Cross-section of the anther of R. missouriense showing dehiscence. Figs. 25-28. Various stages of megasporogenesis in R. missouriense. Figs. 29-31. Showing linear, T-shaped and an isobilateral tetrad of megaspores respectively in R. missouriense. Figs. 32-34. Linear and T-shaped tetrads of megaspores in R. cynosbati. Figs. 35-39. Different stages of megagametogenesis and organised embryo sac in R. missouriense. Figs. 40--44. Different stages of megagametogenesis and organised embryo sac in R. cynosbati. Figs. 45-46. Twin tetrads of megaspores in R. missouriense (ant, antipodals; deg. meg, degenerated megaspore; e. egg; end, endothecium; epi, epidermis; fib, th. ,fibrous thickening; m.L, middle layers; s.n, secondary nucleus; syn, synergid ; t, tannin ; tap, tapetum )

1968-70. Printed at The Bangalore Press, Bangalore-18, by M. S. Narayana Murthy, Secretary, Published by B. S. Venkatachar, Editor, "Proceedings of the Indian Academy of Sciences", Bangalore