ON THE PROBABLE ORIGIN OF THE UNILOCULAR OVARY OF THE CONIPOSITA~ FROM THE STYLIDIACE~ BY K. SUBRAMANYAM (Department of Botany, Central College, Bangalore*) Received April 2, 1951 (Communicated by Dr. P. Maheshwari, F.A.SC.) THE Australasian family Stylidiace~e (Engler, 1908) includes the following six genera: Donatia, Phyllachne, Forstera, Oreostylidium, Levenhookia and Stylidium. The largest genus is Stylidium including 103 species. During the course of my embryological studies on the Stylidiace~e (Subramanyam, 1950a, b; 1951 a) certain important features were noticed in the structure of the ovary, which seem to throw some light on the origin of the unilocular ovary of the Composite. In Donatia Novae-Zelandiae the inferior ovary is typically bilocular (Fig. 1) with the septum extending from the base of the ovary to the top and enclos- ing a number of ovules borne on the axile placenta. In the different species of Stylidium we find a series of stages showing the gradual loss of the septum separating the two locules and this starts from the top of the ovary towards the base. The loss of the septum may be due to its gradual dissolution or incomplete development. In Stylidium graminifolium (Subramanyam, 1951 a) the inferior ovary is bilocular in the lower region but becomes unilocular at the apex (Figs. 16-20). This is because of the incomplete septum or perhaps its dissolution in the upper region of the ovary. Correspondingly, the placentation is axile in the lower region and free central above. A simi- lar condition is met with in S. rupestre (Fig. 2), S. laricifolium (Fig. 3), S. lineare (Fig. 5), S. glandulosurn (Fig. 6), S. hirsutum (Fig. 7)and Oreostylidium subulatum (Fig. 4). Starting from S. rupestre and passing on to S. hirsutum we can trace a series of stages showing the gradual loss or incomplete extension of the septum (Figs. 2-7). Thus in S. rupestre the septum is incomplete at the apex of the ovary (Fig. 2); and in S. hirsutum there is no septum in the upper half of the ovary (Fig. 7). The next condi- tion is reached in Levenhookia dubia (Fig. 10), Stylidium scandens (Fig. 11), S. verticillatum (Fig. 12) and S. schoenoides (Fig. 13), where the ovary is * Part of work done during the tenure of a Junior Research Fellowship of the National Institute of Sciences of India. 327 328 K. Subramanyam FIGS. 1-22 FIGs. 1-14. Longitudinal sections of ovaries of: Donatia Novae-Zelandiae;Stylidium rupestre ; S. laricifolium ; Oreostylidium subulatum , Stylidium lineare ; S. glandulosum ; S. hirsutum ; S. guttatum ; S. imbricatum ; Levenhookia dubia ; Stylidium scandens ; S. verticillatum ; S. schoenoides ; Zinnia. FIG. 15. T.S. of ovary of Downingia. FIG. 16. A tbree-dimensional view of sections of ovary of S. graminifolium at different levels. FIGs. 17-19. T.S. of ovary at levels a, b and c marked in Fig. 16. FIG. 20. L.S. of ovary parallel to septum to show ?ts unilocular nature at the top. FIGs. 21-22. Transverse sections of two ovaries of Stylidium adnatum to show atrophied condition of the upper chamber. [Note.--ln Fig. 1 the longitudinal section is taken at right angles to septum ; in Figs. 2-7 it is parallel to septum. Figs. 1, 2,4, 6--9 and 11-13 after Engler (1908) ; Figs. 15, 21 and 22 after RosGn (1935) ; Figs. 3, 5, 10, 14, 16-20 original]. Origi~z of UJtilocular Ovary of Composi/,~ from So,lidiace~ 329 typically unilocular as a result of the complete loss of the septum. In these forms the ovules are borne on a free central placenta. Further, in Leven- hookia dubia, S. scandens and S. verticillatum the short axis of the free central placenta projects into the locule from the base of the ovary (Figs. 10--12). In S. schoenoides even this is suppressed so that all the ovules are crowded at the base of the locule (Fig. 13). If at this stage there is a reduction in the number of ovules to one, the result will be a condition similar to that of the unilocular ovary of the Composita~ with a single anatropous ovule borne on a basal placenta (Fig. 14). In fact a tendency towards reduction in the number of ovules is also seen in certain members of Stylidiace~e, viz., S. guttatum (Fig. 8) and S. imbricatum (Fig. 9). Further, in these forms the axis of the free central placenta is very thin and slender. There is also another possible line of approach towards the origin of the unilocu!ar condition of the Composit~e. In Stylidium graminifolium (Subra- manyam, 1951 a) where the ovary is bicarpellary, the anterior carpel with its locule is distinctly larger than the posterior (Figs. 16--19). Next, in S. adnatum Ros~n (1935) finds that one of the chambers shows an atrophied condition and does not bear ovules (Figs. 21, 22). He considers it probable that the one-chambered ovary of the Stylidiace~e has been derived from the typically two-chambered ovary of the Lobeliace~e and adds that even among certain Lobeliace~eous members a unilocular condition of the ovary is met with as in Downingia (Fig. 15), though this condition is of a somewhat different nature from that of Stylidium adnatum. So, if in a form like S. adnatum, where one of the loeules become atrophied, there is next a complete suppres- sion of this locule, the result will be the unilocular condition of the Compo- sits. CONCLUSIONS The unilocular ovary of the Composit~ from the Stylidiace~e may have arisen by the gradual suppression or incomplete development of the septum separating the two locules or by abortion of one of the locules. On similar lines Ros0n (1946) has derived the origin of the ovary in the Composita~ from the Goodeniace~e. Hence the unilocular condition of the ovary in the Com- posit~e may be traced from two levels, viz., the Stylidiace~e and the Goodeni- ace~e. It may be also pointed here that the families Lobeliace~e, Stylidiace~e, Goodeniace~e and Composit~e are closely interrelated on embryological grounds (Rosrn, 1935, 1937, 1946, 1949; and Subramanyam, 1950a, b; 1951 a, b). It gives me great pleasure to thank Prof. P. Maheshwarl for going through the manuscript. I also thank Prof. L. N. Rao for kind encouragement and B3 330 K. Subramanyam the National Institute of Sciences of India for the award of a Research Fellowship. SUMMARY It is suggested that the unilocular ovary of the Composit~e may have originated as a result of the gradual suppression or incomplete development of the septum separating the two locules in the ovary of the Stylidiace~e. It is also possible that the unilocular condition of the Composit~e may have been derived as a result of abortion of one of the locules, for, this tendency is already evident in certain species of Stylidium like S. adnatum. LITERATURE CITED Engler, A. .. Das Pflanzenreich. Heft, 1908, 35 B and IV, 278, 1-98. Ros6n, W. .. "Beitrag zur Embryologie der Stylidiaceen," Bot. Notiser (Lund), 1935, 273-78. .. " Beitr/i.ge zur Kenntnis der Embryologie der Goodeniaceen," Acta Horti G6teborgs, 1937, 12, 1-10. .. "Further notes on the embryology of the Goodeniace,e," MeddeL Ft. Gi~teborgs. Bot. Triigd., 1946, 16, 235-49. .. "Endosperm development in Campanulacem and closely related families," Bot. Notiser (Lund)., 1949, 2, 137-47. Subramanyam, K. .. "An embryological study of Levenhookia dubia Sond. in Lehm.," Proc. N3t. Inst. Sci. lndia, 1950 a, 16, 245-53. .. " Development of embryo-sac and endosperm in Stylidiltrtl tenellum Swartz.," Curt. Sci., 1950b, 19, 294. .. "'A morphological study of Stylidium grambdfoliurn Swartz.,'" Lloydia, 1951 a (in press). .. "Flower structure and seed development in Isotama fluviatilis F. vM.," Proc. Nat. Inst. ScL India, 1951 b (in press). &ST.51~Printed at The BandalO#e Pmzss, Bsnjaloz.e City, by O. Sz.]nlvasa Rao, Supor,ntoflden~ ~znd Published by The IndlSo Acmdemy of SollnQOl, B~I3{I~|OrG .