The Inflorescence and Flowers of Dichrostachys Cinerea, W & A
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THE INFLORESCENCE AND FLOWERS OF DICHROSTACHYS CINEREA, W & A BY C. S. VENKATESH (Department of Botany, University of Delhi, Delhi) Received April 14, 1951 (Communicated by Prof. P. Maheshwari, r.A.SC.) THE inflorescences of certain members of the sub-family Mimosoide~e bear polygamous flowers. Geitler (1927) has described this phenomenon in Neptunia oleracea. The results of a similar study of Dichrostachys cinerea, another member of the sub-family, are embodied in the present paper. This plant is of frequent occurrence in the dry forests of India and material collected on the Delhi Ridge last September by Prof. P. Maheshwari was very kindly passed on to me for study. Besides dissections of numerous flowers from several inflorescences, microtome sections of complete young spikes as well as of individual flowers were cut following the customary methods of infiltration and imbedding in paraffin. Some sections were stained with safranin and fast green and others with Heidenhain's iron-alum h~ematoxylin. OBSERVATIONS A portion of a flowering and fruiting twig of the plant is shown in Fig. 1. Exclusive of the stalk, approximately the upper half of the spicate inflorescence bears normal, perfect, bisexual flowers with the floral formula K (5), C (5), A 5, and G 1. The petals are subconnate towards their bases and are bright yellow in colour. The stamens have slender filiform fila- ments. The five stamens opposite the sepals are longer than those oppo- site the petals (Fig. 11). The dorsifixed anthers are four-celled, with the connective prolonged into a conspicuous, stipitate gland (Figs. 17, 18, 29). Four archesporial groups are differentiated in each anther (Fig. 30). The pollen grains in each anther locule are aggregated to form 6 or 7 pollinia arranged in a single fi!e (Fig. 17). The ovary is one-celled and densely hairy (Fig. 12). The long style ends in a dilated, cup-like stigma with a marginal rim (Fig. 13). There are several ovules in two rows on a marginal placenta (Fig. 12). The anther filaments and the style are folded in bud but straighten out and become exserted in the open flower (Fig. 7). B1 183 184 C.S. Venkatesh FIGS. 1-13. Fig. 1. Twig bearing three inflorescences with closed flowers (a), open flowers (b) and fruits (c), x 1. Fig. 2. Part of axis of inflorescence with flowers and bracts removed to show arrangement of scars of perfect flowers (a), flowers of intermediate zone (b), and sterile flowers (c). Fig. 3. Youn.g spike showing compactly arranged flower buds, x 189 Figs. 4-6. Buds of perfect (fig. 4), intermediate (Fig. 5) and sterile (Fig. 6) flowers, x 5. Figs. 7-9. Open flowers of three types, perfect (Fig. 7), intermediate (Fig. 8) and sterile (Fig. 9) x 5. Fig. I0. An open sterile flower with the tassel or staminodes straightened out, x 5. Fig. 11. Two petals and three stamens of a perfect flower, x 5. r~ig. 12. Pistil of a perfect flower; dotted lines indicate position of ovules within, x 2289 Fig. 13. Enlarged stigma, x 70. T/te Inflorescence and Flowers of Dichrostachys cinerea, W & ,4 185 Flowers borne in the lower region of the inflorescence are sterile. The greatly shortened sepals and petals are somewhat pinkish in colour. Anthers are wanting and the bare filaments of the staminodes are greatly elongated and flattened and lie crumpled in bud. They form a dense tassel of tangled, thread-like, purplish-red structures which are much more conspicuous than the sepals or petals (Figs. 1 b, 9, 10). The tips of the staminodes show no differentiation into anthers (Figs. 28, 34). The pistillode presents a reduc- tion series from one with a short style and stigma to a very minute hairy structure without any such differentiation. Ovules are either rudimentary or wanting. The reduction may be abrupt, belated or gradual so that the lowest flowers in an inflorescence may have only the barest rudiment of a pistillode, or a fairly large pistillode with a distinct style and stigma, or one with a very short beak-like style. The demarcation between the upper fertile and lower sterile flowers is not so apparent in the youngest spikes (Fig. 3), but becomes more and me, re conspicuous in the later stages (Fig. 1, a) specially when the flowers open (Fig. 1, b). At first all the flowers are more or less of the same colour, but later the lower sterile flowers turn somewhat pinkish while the fertile upper flowers retain a bright yellow colouration. When in full bloom, the pretty nodding spike shows the bright yellow of the upper half in striking contrast to the red-purple of the lower half. All the flowers in the young spike are compactly arranged, but as it elongates the shorter flowers of the lower half appear to be more loosely arranged (Fig. 1, a). However, at the open-flower stage the lower zone again appears denser (Fig. 1, b) because of the tangled mass of staminodes. Between the two zones described above are a few flowers which are of an intermediate nature. The calyx and corolla present a gradual reduc- tion in size. A few such flowers immediately below the perfect flowers bear stamens with 4-celled anthers but these are slightly smaller than those of the perfect flowers (Figs. 19, 20). Flowers still lower bear very small, variously deformed rudimentary anthers with 3, 2 or 1 loculus only (Figs. 21-25, 31-33). The terminal gland also shows corresponding reduction from a conspicuous stipitate structure to just a blunt, shortened stump (Figs. 25-27). The filaments show a marked tendency to elongate, broaden and twist like the staminodes (Fig. 15). The gyncecium in these flowers is almost normal except for a slight decrease in size. Further down the inflorescence are a few flowers that are apparently female with the stamens devoid of anthers. 186 C.S. Venkatesh Fins, 14-34. Fig. 14. Short and long stamens of a perfect flower, • 5. Fig. 15 Short and long stamens of an intermediate flower, • 5. Fig. 16. Staminode front The In/lorestence a~zd Flowers of Dichrostachys cinerea, W 6" A 187 sterile flower, • 5. Figs. 17-18. Ventral and dorsal views of anther from a perfect flower (dotted lines indicate position of the pollinia within), • 45. Figs. 19-24. Anthers from intermediate flowers with all four loculi intact (figs. 19, 20), with one loculus reduced (Fig. 21), and with two loculi reduced (Figs. 22-24), • 45. Figs. 25-27. Other deformed anthers, • 45. Fig. 28. Tip of a staminode showing lack of anther, • 45. Fig. 29. L.S. anther gland from a perfect flower, x 730. Fig. 30. T.S. perfect anther with 4archesporial groups, • 320. Figs. 31-33. T.S. anthers with 3, 2 and only 1 archesporial group respectively, x 320. Fig. 34. T.S. tip of staminode showing Jack of differentiation of anther, x 320. Of the total number of flowers in a spike, the perfect flowers are the most numerous, the sterile flowers fewer and the intermediate flowers fewest. Counts made on four spikes gave the average of 117 fertile, 34 sterile and 11 intermediate flowers. As expected, in the fruiting spike the twisted pods are confined only to the upper zone (Fig. 1 c). It is clear from the above account that sterilization in the inflorescence is in the basipetal direction. In an individual flower it is centripetal, pro- gressing from the stamens to the pistil. Sterilization in both cases is gradual, the perfect flowers in the spike being separated from the sterile flowers by a few transitional types. SUMMARY The inflorescence of Dichrostachys cinerea is described in detail. In addition to the two externally well-marked zones consisting of the upper perfect and bisexual flowers, and the lower sterile ones, there is a short inter- mediate zone of a few flowers which form a transition between the two. Sterilization of the inflorescence is basipetal; of the flower centripetal. The author expresses his grateful thanks to Prof. P. Maheshwari, for material and guidance and to Dr. B. M. Johri for helpful suggestions. LITERATURE CITED Duthie, J. F. .. Flora of the Upper Gangetic Plain, Calcutta, 1911. Gamble, J. S. .. Flora of the Presidency of Madras, Calcutta, 1915. Geitler, Lothar .. "Zur Morphologie der Inflorezenzen und Bliiten yon Neptunia oleracea," Ber. deutsch, bot. Ges., 1927, 45, 36-39. Hooker, J. D. .. Flora of British India, 1879, 2, Kent, England. .