HISTO-ANATOMICAL ASPECTS REGARDING THE MORPHOGENESIS OF THE CYATHIUM IN TWO SUBSPECIES OF EUPHORBIA MYRSINITES L. (EUPHORBIACEAE JUSS.)

on the Euphorbia cyathium is quite rich, the first histo- anatomical data appertaining to Houard (1906), who studies some floral morphosis produced by larva in Euphorbia cyparissias L., pointing out the structure of the normal and the infested inflorescence. Haber and the collaborators (1925) analyze the vascular origin of the cyathium in some Euphorbia species and adduce an argument in plus for uphold the conception according to that the cyathium is a high specialized inflorescence. Other researchers (Weniger, 1917; Raya & Prakasa, 1975; Gori, 1987; Carmichael & Selbo, 1999) investigate the development of the ovule and the embryogenesis in the representative Euphorbia species. The recent (2004) Papp’s researches regard the structure of the nectary glands of the cyathium. Until us, the Romanian literature of the field includes no study on the anatomy of the Euphorbia cyathium. This article analyzes the cyathium morphogenesis in two subspecies of Euphorbia myrsinites L. from the Romanian flora related to the vascular transition. MATERIAL AND METHODS The material represented by the inflorescences of two Euphorbia taxa (E. myrsinites ssp. myrsinites and E. myrsinites ssp. litardierei), collected from Dobrogea (Romania) was fixed in FEEA mixture and preserved in 70% ethylic alcohol. To observe the changes of the vascular tissues in the cyathium, the histo- anatomical investigations were done on serial cross-sections through this inflorescence, which were performed using the standard paraffin-embedded protocol applied in plant histo-anatomical researches and described by Şerbănescu et al. (1983). Fixed samples were dehydrated by a passage through ethanol/water solutions and then embedded in paraffin at 65?C for 24 hours. The embedded material was cut into 13 µm thick sections with a rotator microtome. The dried serial sections were deparaffinized, rehydrated in serial dilutions of ethanol (100%, 90%, and 70%), coloured with metilen blue and ruthenium red, and finally mounted in Canada balsam. The all permanent slides were analyzed in the light microscopy, using a Novex (Holland) microscope; the micro-photos were made at the same microscope with a Sanyo digital camera. RESULTS From a morphological point of view, the cyathium in both Euphorbia myrsinites subspecies is relatively similar. The nectary glands are bi-cornute, but have a different colour, being yellow (in Euphorbia myrsinites ssp. myrsinites) or red (in E. myrsinites ssp. litardierei). In the cross-sections realized along the cyathium, suggestively notated with alphabetical letters (Fig. 1), successive stages of inflorescence development may be observed. In the lower level (Fig. A), the central axis of the cyathium is delimited by an epidermis (consist of papilla-shaped cells) and comprises a lax cellulosic parenchyma, in which many vascular bundles (consist of a thick procambium between a few phloem elements and xylem vessels) are present; seven of this bundles are located in the central part of the cyathium axis, suggestively named “central vascular bundles”(Fig. A. 1), the other ones being situated at its periphery, taking the name of “peripheral vascular bundles”(Fig. A. 2). At the periphery of the phloem, many laticifers with thick, but cellulosic walls are present. During the ontogenesis of the cyathium, the monostaminate male flowers are first formed (Fig. B); a single peripheral vascular bundle pervades in each primordium of stamen. Simultaneously with the male flowers development, the involucre begins to separate from the central axis, this process being continuous along the inflorescence (Figs. C, D). Finally, the central axis of the cyathium will comprise only the “vascular central bundles”. In the upper part of the cyathium (Fig. D), the involucre is completely separated from the central axis, having an irregular polygon shape, with undulate margins (in transverse section) and presents: 1. external epidermis consist of papilla-shaped cells and stomata with suprastomatal chambers; 2. very lax parenchyma tissue, in which many vascular bundles are present, some of them being solitary, the others forming tangential rows; the latest ones will penetrate the future nectary glands; at the periphery of the phloem, many big laticifers may be observed; 3. internal epidermis, in which the most of the cells are tangentially elongated. At the upper level of the involucre, the nectary glands are completely formed (Fig. E), and consist of an epidermis, a glandular tissue and a lax parenchyma tissue, in which vascular bundles may be observed. The central axis of the cyathium grows in length by the elongation of the cells and finally forms the pedicel of female flower. At the upper level of the pedicel the carpels are formed successively. The completely developed ovary is syncarpous 3- carpellar, 3-locullar; there are cases in which the female flower is infertile (Fig. 2). In each locule a single ovule is formed, the placental position being central- marginal. CONCLUSIONS  The morphogenesis of the cyathium is similar in the both analyzed taxa.  In the first stage of the cyathium morphogenesis, the involucre begins to separate successively from the central axis at the same time with the forming of the primordia of stamens; in each monostaminate male flower pervade a single vascular bundle.  The three carpels appear successively from the central axis and form the ovary, in which the placental position is central-marginally.  The nectary glands of the cyathium are formed from the involucre at its upper level; several vascular bundles of the involucre pervade in the glands.  In the involucre, pedicel of female flower and ovary wall, numerous laticifers could be observed. BIBLIOGRAPHY

CARMICHAEL, S., SELBO, M. SARENA, 1999 – Ovule, embryo sac, embryo and endosperm development in leafy spurge (Euphorbia esula), Can. J. Bot., 77, 4: 599-610

EMBERGER, L., 1960 –Les végétaux vasculaires. t. II, Traité de Botanique systématique (de M. Chadefaud et L.Emberger), Libraires de L’Académie de Medicine , Paris

GORI, P., 1987-The fine structure of the developing Euphorbia dulcis endosperm, Ann. Bot., 60: 563-569 HABER MOESEL, JULIA, 1925, - The anatomy and the morphology of the flower of Euphorbia, Ann. Bot., 39:656-707

HOUARD, M. C., 1906- Sur l’anatomie de la galle de l’involucre des

Euphorbes, Rev. Gen. Bot., 18: 67-81 PAPP NORA, 2004 – Nectar and nectary studies son seven Euphorbia species, Acta Bot. Hung., 46, 1-2: 225-234

PARROT, G., 1947- Quelques remarques sur l’inflorescence d’Euphorbia peplus L., Bull. Soc. Bot. France, 94, 9: 424-427 RAJA RAJESWARI RAO, K., PRAKASA RAO, P. S., 1975 - Embryo development in Euphorbia peplus L., Current Science, 44, 1: 57-59 ŞERBĂNESCU -JITARIU GABRIELA, ANDREI M., MITROIU- RĂDULESCU NATALI, PETRIA ELENA, 1983 – Practicum de biologie vegetală, Ed. Ceres, Bucureşti

WENIGER, WANDA, 1917 –Development of embryo sac and embryo in Euphorbia preslii and E. splendens, Bot. Gaz., 63, 4: 266-281 E. myrsinites ssp. myrsinites cyathium (orig. photos): 1- Macroscopic aspect; A, A. 1, A. 2, B, C, D – Serial cross-sections (from base to tip) through the cyathium; E- Longitudinal section through a nectary gland of the cyathium; 2- Cross-section from the ovary of the female flower of the cyathium (scale bars = 50μm)