To View Fulltext

A CONTRIBUTION TO THE EMBRYOLOGY OF SONNERATIACEAE. BY JILLELLA VENKATESWARLU. (From the Department of Botany, Benares Hi~,du U~iz,ersity, Benares.) Received April 14, 1937. (Communicated by iV[r. A. C. Joshi, M.sc.) SONNERATIACEm iS a small family of the Myrtifloreae. According to Engler and Prantl (1898, 1908), it includes four genera, Sonneratia, Duabanga, Xenodendron and Crypteronia, comprising about a dozen species. All these are found in the tropics, the monotypic genus Xenodendron being confin6d to New Guinea and the rest being mostly restricted to the Indo-Malayan region. Hutchinson (1926) in his recent system of classification has sepa- rated the genus Crypteronia into a separate family Crypteroniacem and the family Sonneratiaeem as defined by him includes only three genera. Bc:ntham a!~d I~ooker (1%2-67), on the other hand, include these genera in the family Lythracem, to which there is little doubt that these are very closely related. As the writer had been recently studying the embryology of the family Lythracem (Joshi and Venkateswarln, 1935 a, 1935 b, 1935 c, 1936), it was thought desirable to study the family Sonneratiacem also from the comparative point of view and to see how far its embryological features agree with those of the Lythracem. The previous work on this family is limited to an investigation on Sonneratia apetala Linn. by Karsten (1891). tIis observations, however, are very fragmentary and also partly erroneous as pointed out by me in preliminary notes (Venkateswarlu, 1936a, 1936b) relating to the plants described in the present paper. The present paper deals with the two chief genera of the family, namely, Duabanga and Sonneratia. The species studied are Duabanga sonneratioides Ham., and Sonneratia apetala Lamk. The material of the former was collected by me from plants growing in the Royal Botanical Gardens, Sibpur, Calcutta, during the months of April 1933 and May 1935 and was later supplemented by a fresh amount kindly sent by Mr. I. Banerji of Calcutta University. The material of Sonneratia apetala was collected by me in April 1936 from plants growing wild in the salt marshes near Calcutta. Material of both the plants was fixed in Nawaschin's fluid and Allen's modified Bouin's fluid. Haidenhain's iron-alum-h~ematoxylin with or without a counter-stain of light green was used for staining the sections. 206 ./1 Conlribution to the Em3ryoZogy of Souneraliace~ 207 Development and Structure of Pollen. The primary archesporium consists of a sub-epidermal row of cells in each of the four lobes of the anther, as may be seen from the longitudinal and transverse sections of young anthers (Figs. 1 and 2). In Sonneratia apetala there are about 10 archesporial cells in this row, in Duabanga sonneratioides about 20-25 cells. The first division of the primary archesporial FIGS. 1-7. Fig. 1, D~abanga sonneratioides, longitudinal section of an anther-lobe showing the primary archesporium. Some archesporial cells near the bare have cut 'off parietal cells. Figs. 2-4, Sonneratia apetala, transverse sections of various stages in the development of an anther-lobe. Fig. 5, Sonneratia apetala, 1-nucleate pollen grain in section along tbe shorter diameter. Figs. 6-7, Duabanga sonneratioides, bi-nucleate pollen grains cut along thelonger and the shorter diameters respectively. Figs. 1 & 4, • 450 ; Figs. 2 & 3, • 600; Figs. 5--7, • 1,600. 208 Jillella Venl~ateswarlu cells is periclinal and results in an outer layer of primary parietal cells and an inner layer of primary sporogenous cells. The primary parietal ceils by periclinal divisions ultimately form 3-4 cells thick wall between the epidermis and the tapetum (Fig. 4). The inner layers of the wall are formed by narrow flattened cells which get crushed with the growth of the tapetum and sub- epidermal wall layer. The primary sporogenous cells undergo a number of divisions in all planes and give rise to a large amount of sporogenous tissue. The origin of the tapetum could not be followed definitely. Usually it consists of a single layer of cells, but sometimes here and there it is 2-seriate just as was seen in some Lythrace~e (Joshi and Venkateswarlu, 1936). At about the time when pollen-mother cell nuclei enter synizesis, the nuclei of the tapetal cells divide once mitotically, just as in the majority of other angiosperms (Cooper, 1933) and become bi-nucleate. During the formation of pollen grains, the anthers undergo the usual increase in size and the cells of the epidermis and the sub-epidermal wall layer divide anticlinally to keep pace with the general increase in size of the anther. The sub-epidermal layer in the later stages develops into the fibrous endothecium. The wall layers below it are crushed and the tapetum degenerates without forming any periplasmodium. The pollen grains separate and round off before the differentiation of intine and exine takes place. The first division of the nucleus in the pollen grains takes place after the full differentiation of intine and exine and the attainment of almost their maximum size. In Sonneratia apetala, it takes place just before the dehiscence of the anther. At the time of shedding, the pollen grains are 2-nucleate. No membrane or wall between the vege- tative and generative nuclei is seen at this stage. The mature pollen grains are "slightly elongated along one diameter. The exine is thick. The surface is smooth in Duabanga sonneratioides, while it is rather rugged in the case of Sonnera~ia apetala. Further the pollen grains of the two plants differ remarkably in size. The mature pollen grain of Duabanga sonneratioi4es measures about 16 ~ along the shorter diameter and 20/z along the longer diameter. In Sonneratia apetala it measures about 30/z along the shorter diameter and 35/~ along the longer diameter. There are 3 germ pores in the exine of each pollen grain arranged in an equatorial fashion. Their sections, therefore, along different diameters give rise to different appearances just as in Ammania baccifera (Figs. 5-7). The intine protrudes out through the germ pores. The pollen grains of Sonneratia apetala have been tested for starch, which is present in consider- able amount. A Contribution to the Embryology of SonmraEacece 209 Degenerations in the young sporogenous tissue in the anthers are quite common in Sonneratia apetala. Structure of the G,'na~cium and the Ovule. The ovary is semi-inferior. Usually it is described to be many-celled (10-20-celled) in Sonneratia (Engler and Prantl, 1898; Hooker, 1879, Haines, 19,~ [luring the present investigation, in Sonneratia apetala it was found to be only 5-6-celled (Fig. 8). Karsten (1391) also describes it to be 5-celled. In Duabanga sonneratioides, according to t~ngler and Prantl (1898), Hooker (1879) and Haines (1922), the ovary is 4-8-celled, but in the material examined by the writer it was found to be often up to 10-celled. In Sonneralia apetala the midribs of the carpels, which alternate with the septa, slightly protrude into the loculus of each carpel (Fig. 8), though these are not as prominent as in the ovary of Lagerstroemia (Joshi and Venkateswarlu, 19:35@ The placentas are axile and very much enlarged. There is no suggestion of a parietal or sub-basal plaeentation as described by Rendle (1925). The style is bent upon itself in bud as m some Lythraeem (Lawsonia, Neswa, Lagerstrwmia, etc.) and bears a 6-10-lobed, capitate stigma in Duabanga sonneratioides and a large, umbrella-shaped stigma in Sonneratia apetala. In Sonneratia apetala the ovules are anatropous with a small bend in the chalazal region towards the raphe, a fact" also observed by Karsten (1891). They are also slightly flattened towards this side. The funicle is very long and in the chalazal region there is often a small space left between the outer and the inner integuments. The space may be only on one side (Fig. 10) or on both the sides (Karsten, 1891, Fig. 88). The ovules of Duabanga sonneratioides are also anatropous in their form, but they are completely cylindrical. They develop long prolongations of their integuments at either end, so that the seed becomes divided into a body or nucleus and two tails (Fig. 11). In Sonneratia apetala, there is no such development. In both plants, the ovules are two-integumented and ascending. However, one case was met with in Sonneratia apetala, where one of the ovnles was found to be in the orthotropons condition at the megaspore-mother cell stage, while all the neighbouring ovules had become anatropous. This ovule also deviates from the rest in only having a single integument (Fig. 9). This exactly coincides with an exceptional case observed in the case of Nescea nwrtifolia (Joshi and Venkateswarlu, 1936, Fig. 50). In Duabanga sonneratioides occasionally an ovule is found to be descending. 210 Jillella Venkateswarlu FIGS. 8-14. ,,4 Contributiou to the Embryology of Sonneratiace~ 211 Figs. 8-10.--Sonneratia apetala. Fig. 8, transverse section of an,, overy showing 6 loculi and the carpel midribs projecting slightly into the cavities ; Fig. 9, part of Fig. 8 on a higher magnification showing an arthotropous ovule besides a normal one ; Fig. 10, longitudinal section of an ovule at the mature embryo-sac stage showing its form, micropyle and the air space between the two integuments near the chalaza. Figs. ll-14.--Duabanga sonneratioides. Fig. 11, longitudinal section of an ovule, showing the form, micropy'le, nucellus, conducting strand and prolongations of the integuments ; Fig. 12, transverse section of an ovule showing two nueelli within c~mm~n inner and outer integuments; Fig. 13a, longitudinal section of the upper part of an old ovule showing the long, straight mieropyle; Fig.

Load more