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Embryology of Helichrysumrupestre (Rafin.) DC. var.messerii Pignatti (Inuleae,Asteraceae)Rosalba Villari aa Istituto di Botanica-Orto Botanico , Via P. Castelli2, I-98100, Messina, ItalyPublished online: 14 Sep 2009.

To cite this article: Rosalba Villari (1987) Embryology of Helichrysum rupestre(Rafin.) DC. var. messerii Pignatti (Inuleae, Asteraceae), Giornale botanicoitaliano: Official Journal of the Societa Botanica Italiana, 121:1-2, 27-40, DOI:10.1080/11263508709431643

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Giorn. Bof. Ita!., 121: 27-40, 198i

Embryology of Helichrysum rupestre (Rafin.) DC, var. mcsserii Pignatti (Inuleae, Asteraccae)

ROSALBA VILLARI Istittito d i Bofatxica-Orio Bofatxico, Via P. Casfelli 2, 1-95100 hlessitxa, l faly

Arcepfed: IG ]anuary 1981;

ABSTRACT. - Embryology of Helichrysiraz rrrpestre var. rizesserii Pignatti has been studied. The anther is tetrasporangiate and its \\vll development conforms to the Dicotyledonous type. The tapetum corresponds to the Periplasmodial type and its uniseriate cells show a dual origin. hlicrosporocytes are linearly arranged; tetrahedral, isobilateral or decussate pollen tetrads were observed. The ovule is anatropous, unitegmic, tenuinucellate and endotheliate; the peripheral nucellar cells begin to degenerate after the tetrad stage, when the endothelium is already diffe- rentiated. This integumentary layer surrounds the mature embryo sac almost com- pletely remaing uniseriate with uninucleate cells after fertilization. The unicellular ovular archeosporium functions as the megaspore mother cell. The chalazal megaspore of the linear tetrad develops into a Polygonum-type embryo sac. The synergids are hooked at their micropylar region and show a filiform apparatus before fertilization. At this stage the primary antipodal cells increase in number. Unusual nuclear arran- gement as well as precocious cell mall development has been observed in a few young gnmetophytes; in a single ovule a coenocytic megagametophyte has been observed with supernumerary nuclei and anomalous vacuolation. Fertilization is porogamous. Endosperrn development is of Nuclear type. The embryogeny conforms to the Asterad type.

Key ruords: Anther 'and ovule development, Asteraceae, embryology, embryogenesis, Helichrysutn rirpesfre var. messerii.

INTRODUCTION

Embryological observations on the genus Helichrysrriiz hlill. corr. Pers. mere carried out firstly by DAHLGREN (1920), who observed the occurrence of super- numerary antipodal cells in the embryo sac of Helichrysuitz aizgrrstifolirriiz DC., as well as an embryonal development in the absence of endosperm. SCHNARF (1931) reported a cellular type of endosperm development in a Helichrysrriiz sp. studied by HOFMEISTER (1858). TOSGIORCI (1936, 1942) examined the development of the female gametophyte in Helichrysiritz areizarirriiz Moench and in H . bracteattriiz Andr.

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Both species showed a single magasporocyte and supernumerary antipodal cells; the megagametophyte development was of Polygonum-type in H . areizarizrin and of Pyretrum partenifolium-type (Drusa-type according to DAVIS, 1966) in H . bracteatzrm. PANDEY (1980) studied structure and developmental pattern of the endothelium in some members of the Compositae. He quoted H . brmteatzrrn among the species showing a single layered endothelium throughout seed development; he also stated that this integumentary layer degenerates or persists in form of a non- cellular pellicle appressed to the outermost endosperm layer, when the seed is mature. SKVARLA et al. (1977) examined the pollen morphology in H . dnveizportii F. Muell. with TEM.

The present investigation gives an account of some embryological aspects of Helichryszrm rrrpestre var. iizesserii Pignatti (1979), an endemic entity for Marettiino (Egadi Islands, West Sicily).

This entity, as H . rirpestre DC. var. perzdzrlrrm (Presl.) Fiori, has been previously examined both cytologically (2n=28) (D’AhiATO, 1971) and anatomically (FRANCINI & MESSERI, 1955-56).

hlATERIALS AND METHODS

Flower heads of different ages were collected from different plants of Hefichrysrriiz rupestre var. tizesserii growing in Marettimo (Egadi Islands).

The material was fixed in formalin-acetic acid-alcohol (FAA 70%) and embedded in paraffin using the standard technique ( JOHANSEN, 1940). Serial longitudinal and transverse sections of complete capitula and single florets were cut a t a thickness of 7-10 prn and stained in Heidenhain’s hematoxylin. Voucher specimens have been deposited in the Herbarium of Messina (hlS), Italy.

OBSERVATIONS

Floral morphology

The hemispheric capitula of H . rrrpestre var. messerii have a slightly convex receptacle bearing 32-55 tubulate florets with acropetal development.

The floral parts in each floret differentiate in the following sequence: corolla, pappus, stamens, carpels and ovule (Figs. 1-4).

The flower heads are heterogamous and show .8-11 peripheral or sub-peripheral pistillate filiform florets. They differ at anthesis from the monoclinous ones because of the zygomorphic corolla-tube and the poorly developed stylar nectary. The pistillate florets can be distinguished also during their early differentiation for they do not form stamina1 primordia (Fig. 5 ) .

As a rule, the two carpellary protuberances (Fig. 3 ) fuse successively giving

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rise to a syncarpous gynoecium with a solid style of Senecio type (MERXMULLER

el al., 1977). The inferior ovary is unilocular and normally produces a unitegmic, tenui-

nucellate, anatropous ovule (Figs. 4, 13, 14), which nearly fills the locule. I n two instances two ovules in the same ovary (Figs. 29, 30) have been observed.

The ovary mall has two vascular traces. I n the basal region outer epidermal cells are differentiated at a young stage (Fig. 4), which later become enlarged and their cell walls thicken. These cells were also observed in ovaries containing atypical ovules detached from the ovary wall (Fig. 34).

Both monoclinous and pistillate florets are chasmogamous and pappose when mature. During the anthesis the five stamens remain confined within the corolla-tube with only the apical anther appendages exserted. Basal hair-like anther appendages are also present.

The tetrasporangiate anthers remain joined together owing to the adhesion of epidermal cuticle on adjacent anthers (Fig. 8).

Microsporaagiutir atid titale gatiretopbyte

A young microsporangium shows a layer of primary parietal cells just below the epidermis, inside of which lies a single row of primary sporogenous cells (Fig. 6). During further development, the primary sporogenous cells undergo repeated trans- verse divisions, so one row of pollen mother cells develops in each locule (Fig. 7).

The cells of the primary parietal layer, in the meantime, divide periclinally (Fig. 6) giving rise to two secondary parietal layers; the outermost cells divide again periclinally forming the endothecium and the middle layer (Fig. 7), while the inner- most parietal cells develop into tapetal cells.

The periclinal divisions observed in the connective cells adjacent to the sporo- genous tissue (Fig. 6), led us to conclude that the concentric tapetal layer is of dual origin.

During the maturation of the microsporocytes, all the cells of the parietal layers, except the tapetal ones, become stretched and flattened. The cells of the middle layer become compressed before the onset of meiosis in the microspore mother cells and the anther simulates a Reduced-type wall (Fig. 8).

The uniseriate tapetal cells derived from parietal or connective cells show a similar differentiation: they become binucleate during prophase I and later multinu- cleate iFig. 8), their nuclei usually fusing in a later stage (Figs. 11, 12). The tapetal cells become periplasmodial during early pollen development (Fig. 12); n o traces of tapetum have been observed when the pollen is three-celled. At this stage the endothecial cells appear radially enlarged and show thickened inner tangential walls.

Microsporogenesis occurs as usual: the resulted microspore tetrads are mostly tetrahedrally arranged (Fig. 8); however, decussate or isobilateral arrangements have also been observed (Figs. 9, 10).

R. VILLARI - Ernbrjology of Helichrysrim rirpestre t'ar. ' messerii 29

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Ovule arid female gametopkyle

The single archesporial cell becomes differentiated in the ovular primordium before the initiation of the integument (Fig. 13). As always in this family, during iurther ovular development the archesporial cell increases in size and develops into the fuctional megasporocyte. This undergoes meiosis when the ovule reaches the anatropous position (Fig. 14). At this stage the integument has already grown beyond the nucellus and the innermost integumentary layer differentiates into the endo- thelium.

The four megaspores have the same location and volume as the megaspore mother cell in prophase; they are always arranged in a linear row. The micropylar cells soon degenerate, whereas the chalazal one enlarges (Fig. 15) and develops into an eight-nucleate embryo sac of Polygonum type.

Increase in size of the functional megaspore is accompanied by degeneration of the peripheral nucellar cells (Figs. 15, 16), whose remnants can be seen in the extreme chalazal region of the organized gametophyte (Fig. 17).

The mature gametophyte is spindle-shaped and shows elongate synergids with their hooked apical portion protruding into the micropyle; the egg cell is pear-shaped and soan reaches its typical polarity. The central cell is large and vacuolate with the polar nuclei centrally located. The three antipodal cells are arranged in a T, the justaposed ones smaller, with a dense and scarcely vacuolate cytoplasm when compared to the chalazal antipodal cell (Fig. 17).

A t the time of fertilization the synergids exhibit the filiform apparatus; the central cell is evidently vacuolate and shows the secondary nucleus close to the egg cell (Fig. 18). At this stage five to twelve uninucleate antipodal cells are arranged in

Figs. 1-5 - Helichrysrrnl rrrpestre var. iuesserii. Floret development. Fig. 1 - Longitudinal section showing petal primordia (pp) and pappus initials (arrows). x 708. Figs. 2, 4 - Longitudinal sections of monoclinous florets in different stages. x 305, s 472, and x 487, respectively. c=corollary teeth; st=staminal primordia; (*)=initials of carpellary protuberances; cp=carpellary protuberances; op=ovular primordium; vt=rascular traces; arrows indicate the differentiating outer epi- dermal cells in the basal region of the ovary wall. Fig. 5 - Young pistillate filiform floret (oblique section). x 535.

Figs. 6-12 - Anther locule development and microsporogenesis. Fig. 6 - Cross section of a young locule showing the primary parietal layer between the epidermal layer (Ep) and the primary sporogenous cell. Note periclinal division in a parietal cetl. Arro\vs indicate a young tapetal cell derived from a connective cell. x 1,579. Fig. 7 - Longitudinal section of part of a locule showing epidermis, three parietal layers (pL) and uniseriate pollen mother cells. x 1,367. Fig. 8 - Cross section of adjacent locules of contiguous anthers with marging cuticles (a ) at tetrad stage. Note multinucleate tapetal cells and compressed cells of the middle layer (arrows). x 1,428. Figs. 9, 10 - Tetrads of decussate and isobilateral microspores. x 2,005, and ~ 2 , 4 0 6 , respectively. Fig. 11 - Parietal tapetal cells (arrows) at stage of uninucleate microspores (LS). x 1,034. Fig. 12 - Cross section of a locule at stage of mononucleate pollen grains. Note epidermis, flattened endothecial cells and periplasrnodial tapetal cells ($0. s 1,606.

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two parallel rows. They have always been observed at the chalazal end of the embryo sac. Presumably, all the primary antipodal cells undergo division followed by cytokinesis, although mitosis has been observed only in the chalaza1 antipodal cell.

Some anomalous features have been observed in developing embryo sacs (Figs. 30-33). A few ovules showed young degenerating gametophytes and in a single instance we observed an obliterated embryo sac flanked by a multiseriate endo- thelium.

Ovules that were detached from the ovary wall containing a mature embryo sac were also sometimes seen (Fig. 34) in both pistillate and monoclinous florets. These ovules, like the normal ones, showed funicular vascular strands extending almost to the chalazal end and enlarged integumentary cells close to the uniseriate endothelium (Figs. 18, 34).

Ferfilizaiioiz, endosperuz and embryo

Fertilization is porogamous and the pollen tube persists for a while after fertilization (Fig. 20). The receptive synergid soon degenerates. Moreover, the remnants of both synergids persist in the embryo sac till the two-celled stage of The proembryo (Figs. 20, 22). The secondary antipodal cells appear to remain alive until the formation of a globular proembryo (Fig. 24).

The endothelium remains uniseriate with uninucleate cells that appear elongated and distorted when the embryo becomes heart-shaped (Fig. 28). After fertilization, the integumentary cells adjacent to the endothelium become disorganized, at first forming a periendotheliar zone (Fig. 18) and later a lysigenous space (Fig. 24).

The endosperm is at first nuclear and the primary endosperm nucleus divides

Figs. 13-18 - Ovule and megagnmetophyte (LS). Fig. 13 - Young ovule showing unicellular archeosporium (A,) Arrowheads indicate initials of the integument on the an- tiraphal region. ow=ovary wall. x690. Fig. 14 - Anatropous ovule showing the megaspore mother cell encircled by uniseriate nucellar cells. ow=ovary wall x 405. Fig. 15 - Ovule with enlarged chalazal megaspore. Arrows indicate the remnants of degenerating micropylar megaspores and peripheral nucellar cells. x620. Fig. 16 - Binucleate embryo sac limited by the endothelium (En). x870. Fig. 17 - Primary antipodal apparatus (An) with a vacuolate chalazal cell. Note remnants of the chalazal nucellar cells. x 1,203. Fig. 18 - hiature embryo sac with supernumerary antipodal cells (An) and filamentous apparatus larrow- heads) on the hooked synergids. Pz=periendotheliar zone; E=egg cell; SN=se- condary nucleus. x 479.

Figs. 19-21 - Endosperm. Fig. 19 - Rare mitosis in a four-nucleate endosperm (NE). x 505. Fig. 20 - Typical aspects of micropylar endosperm cells at twocelled proembryo stage. Note the remnants of the pollen tube (*) and of synergids (DS) sur- mounted by the filamentous apparatus. x708. Fig. 21 - Haustorial aspect of a micropylar endosperm cell (arrowheads) at eight-celled proembryo stage. CE=cel- M a r endosperm. x 566.

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earlier than the zygote. The resulting two endosperm nuclei take up a position close to the nucleus of the polarized zygote; they normally divide synchronoisly in the same plane forming four nuclei around the zygote or the long basal cell of the bicellular proembryo. Thus, the apocytial endosperm cell mantains the same polarity as shown before fertilization. I n a single embryo sac the four endosperm nuclei have been observed dividing synchronously (Fig. 19). More frequently, four vacuo!ate and uninucleate endosperm cells are seen surrounding the bicellular proembryo (Fig. 20). One or two of these are unaccompanied by cell walls in the chalaza1 region.

When the proembryo has already formed the quadrant (Fig. 24), the micropylar endosperm region consists of numerous elongate cells, some of which extend to the base of the micropyle (Fig. 21). I n contrast, the endosperm in the mid-chalaza1 region becomes cellular at a later stage and its cells appear to be larger and more highly vacuolate than the micropylar ones.

A peripheral layer of endosperm showing narrow, anticlinally elongated cells has been observed at the young globular embryo stage, below the persisting endo- theliar cells (Fig. 26). During, late embryogeny the endosperm cells adjacent to the embryonic head have degenerating nuclei (Fig. 28).

Embryo development follows the Asterad type: the first division of the zygote results in the formation of a small apical cell (ca) and a long basal cell (cb) (Fig. 22). The apical cell divides longitudinally, while the basal cell is cut transversally forming the cells in (Fig. 23) and ci.

The daughter cells of the terminal tier as well as cell iu, divide longitudinally, while ci produces the superposed cells IZ and it’ (Fig. 24). The cells of the three upper tiers continue to divide longitudinally, while cell 11’ divides transversally giving rise to o and p (Fig. 25); this latter represents the mother cell of the suspensor and i t shows, like i z ’ , ci, and cb, a marked vacuolate micropylar portion.

Cell segmentations occur almost simultaneously in all the proembryonal cells up to the fourth generation (Figs. 23, 24), later they proceed asynchronously (Figs. 25-28).

After formation of the protodermal cells in the two upper tiers (Fig. 26), cells derived from b divide more actively than those derived from u. Thus, in a

Figs. 22-28 - Embryo development. Fig. 22 - Fertilized embryo sac showing a two-celled proembryo. The filamentous apparatus surmounts a degenerated synergid. x 566. Fig. 23 - Head of a fourtelled proembryo. x991. Fig. 24 - Persisting antipodal cells (An) and endosperm encircling an embryo of the third generation. Pz=peri- endotheliar zone; Ls=lysigenous space; En=endothelium. s 549. Fig. 25 - Longi- tudinal section of a proembryo after the fourth cell generation. The cells a are forming the dermatogen initials. x 739. Fig. 26 - Young globular embryo showing three-celled suspensor (s). Arrowheads indicate the differentiating peripheral endo- sperm cells. de=dermatogen. x 566. Fig. 27 - Globular embvo with periblem (pe) and plerome (pl) initials. x775. Fig. 28 - Heart-shaped embryo showing coty- ledonar and stem apes regions. Note in tier n the initial cells of the rcot cortex (iec) and in tier o the first cells of the root cap (co). x519. Lettering of em- bryo according to SOULCES (1948), Bars = 14.5 Iim.

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globular embryo, i t is possible to distinguish the cotyledonar (pco) and the stem tip regions. A t this stage the four innermost cells of tier i i z are already transversally divided, so that the initials of periblem and plerom of the hypocotyledonary region can be easily identified (Fig. 27).

Together with the development of the globular embryonic head, cell p divides transversally to form a suspensor, which consists normally of a row of four to seven cells. The basal suspensor cell (Fig. 26) always appears to be enlarged, except in one case in which a biseriate suspensor was observed.

When the embryo is heart-shaped, the initials of the root cortex ( iec) in tier i z and the first cells of the root cap (co) in tier o can be seen (Fig. 28).

DISCUSSION

The floral structures in H. rtcpestre var. iizesserii show the same developmental sequence described for Blzruzea laciiziata L. (BANERJI, 1942 in KAPIL & SETHI, 1962).

The occurrence of modified outer epidermal cells in the basal region of the ovary wall has been noticed also in Lnggera pterodoiita Benth. , Aiznphalis bzisiza Hand. and in Vicoa auticulata Cass. (PULLAIAH, 1979), where it has been inter- preted ns an abscission layer.

As in the Inuleae so far investigated, with the exception of Blrriizea iiieiizbratzacea DC. (PULLAIAH, 1979), the anther of Helichrysrriiz is tetrasporangiate and its n d l development follows the Dicotyledonous type (DAVIS, 1966; PULLAIAH, 1983). Although a dual origin of the tapetal cells has not been reported for other members of Asteraceae (PULLAIAH, 1979; 1983), according to BHANDARI (1984), this fea- ture could be of normal occurrence in most Angiosperms.

Figs. 29-30 - Reconstructions of atypical ovaries bearing two anatropous ovules in the same locule (L). Fig. 29 - Ovules at the tetrad stage. x228. Fig. 30 - The ovule drawn with darker line shows the pollen tube (arrowheads) in the micropvle and a young degenerated gametophyte (dG) flanked by the uniseriate endothelium (En). Note typical funicular vascular trace (vt) extending to the chalaza1 end. The subjacent ovule outlined shows the nucellar lobe (NL). x 128.

- Detail of nucellar lobe of Fig. 30. The tetranucleate coenomegaspore (car) is encircled by deqenerating peripheral nucellar cells (pNC). Note the well developed endothelium (En). x 795.

Figs. 32-33 - Schematic drawings of anomalous gametophytes observed in ovaries with a single ovule. Fig. 32 - Atypical vacuole (*) and cells (arrows) in the chalnzal region of a G tetranucleate, gametophyte from a pistillate floret. x68-1. Fig. 33 - The coenocytic megametophyte (G) shows unusual vacuolation and supernumerarv nuclei. Arrows indicate the pollen tube in the micropyle. pKC=peripheral nucellar cells; En=endotheliurn. x 283.

Fig. 31

Fig. 31 - Reconstruction of an atypical mature ovule detached from the ovary wall from a monoclinous floret. G=mature embrvo sac; Pz=periendotheliar zone; vt =va- scular trace; o\v=ovary wall; mc=modified epidermal cells. s 100.

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The anthers become syngenesious during their development as observed among the Inuleae in Podolepis Labill. and in At~zrizobiii~~z alattir7z R.Br. (DAVIS, 1961 a; 1962); however, we did not observe the hyaline membrane noticed in Helinrzthris ariizrizis (Heliantheae) (NANDA & GUPTA, 1976).

As always in the family, the ovule is anatropous, unitegmic, tenuinucellate and endotheliate. The ovular hypodermal archesporium differentiates before the initia- tion of the integument and is unicellular, as reported for H. arettnritiin (TOXGIORGI, 1936).

The chalazal megaspore in the linear tetrad develoDs into a monosporic, eight- nucleate gametophyte of Polygonum type, as reported for the members of Inuleae so far investigated (PULLAIAH, 1979), escept for H . bracteatrim (TOSGIORGI, 1942) and Atiitizobitim alaititn (AVANZI, 1918; DAVIS, 1962). Regarding Leonfodon hi- spidris L. (BERGhIAN, 1935) quoted by PULLATAH (1979), it is a member of Lactuceae (TOMB, 1977).

The degeneration of micropylar megaspores and of apical nucellar cells generally occurs during the enlargment of the functional megaspore, which evolves into an enormous mononucleate gametophyte, as observed in H . arericrirtm (TOSGIORGI, 1936).

The uniisual division occurring in highly vacuolate antipodal cells has also been reported in Podolepis (DAVIS, 1961 b).

The occurrence of supernumerarv antipodal cells at the time of fertilization has been observed in all the members of the genus so far investigated, as well as in some Inuleae. I n our plant, as obscrved for B!tirnea tizeiiibraizncea (PULLAIAH, 1979), the supernumerary antipodal cells do not enlarge after fertilization and persist up to the time of formation of the globular embrvo. The persistence of the antipodal cells nfter fertilization also seems to be closely linked with endosDerm development

Anomalous gametophytes among the Inuleae have been recorded in Inrr ln helerrirrriz L. (TOSGIORGI, 1937) and in Ami~iobiri~rz ahtzrm (AVANZI, 1948), in which the occurrence of supernumerary polar nuclei has been related to the lack of differen- tiation of antipodal cells. I n Helichrysrinz me observed a few irregularities either in megasDorogenesis o r in megagametogenesis.

T i e structure and behaviour of the endothelium after fertilization is conforms to that of H. brncieattitrz (PANDEY, 1980) and other Inuleae so far investigated, except for Blrrtizen malnbarica Hook. f. (PuLLAIAri, 1979), which shows a niulti- layered endothelium in the chalaza1 region. I n one instance we observed a multi- seriate endothelium encirclinp, a degenerate gametoDhyte, as occurs in some Aste- raceae (KAPII. & TIWARI, 3978; PANDBY, 1980; CICHAN flr PALSER, 1982).

Among the Asteraceae the occurrence of mature ovules detached from the ovary wall has been observed only in unDollinated flowers of Cichorizrriz intybtis L. (Lactu- ceae) (CICHAN & PALSER, 1982).

The present study shows that endosperm development follows the Nuclear type, as seen in some soecies of B!rtrriea (CHENNAVEERAIAII & PATIL, 1971; PULLAIArI, 1979) and in Amfertnaria (STEBBINS, 1932; DAVIS, 1966), and endosperm cell \valls

(Cfr. KAPIL flr B~IATNAGAR, 1976; \VILLEhlSE & VAN \VENT, 1984).

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are generally formed after the second nuclear generation. The haustorial cells in the micropylar region of the embryo sac seen at the young, globular embryo stage are of endosperm origin, whereas in A h z o b i t r m (DAVIS, 1962) a surviving synergid has been observed which increases in size but does not extend into the rnicropyle.

As usually occurs in the family (PULLAIAH, 1983), embryogenesis follows the Asterad type (JOHANSEN, 1950).

Acktrozoledgements. - The author is grateful to Prof. hiax H. Hommersand, Department of Biology, University of North Carolina at Chapel Hill and Prof. G. Tripodi, for their comments and critical reading of the manuscript. Appreciation is extended to hlr. Casella and hlr. Costa for their assistance in preparation of drawings and photographs.

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AVANZI hl.G., 1948 - Osservazioni cito-embriologiche sir Amtnobiiinz alafiim R.Br. (Asferaceae).

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R. VILLARI - Etnbryology of Helichryszinz riipestre vat. rnesserii 39

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RIASSLJNTO

Enzbriologia d i Helichrysrittz rripesfre (Rafin.) DC. var. messerii Pigttaffi (Inrileae, Asferaceae). - I1 lavoro illustra lo sviluppo dell’antera e quello dell’ovulo in una inulea endemica dell’isola di hlarettimo (Isole Egadi). L’antera & tetrasporangiata, la sua parete presenta uno sviluppo di tipo Dicotiledone e le cellule del tappe to divengono periplasmodiali durante Ia ma- turazione del polline. I microsporociti sono disposti in una sola serie e danno origine a micro- spore con disposizione tetraedrica, isobilaterale o decussata. L’ovulo 5 anatropo, unitegumentato, tenuinucellato ed endoteliato. Le cellule nocellari periferiche iniziano a degenerare dopo la differenziazione dell’endotelio, che persiste anche durante I’embriogenesi. 11 rnegarchesporio i: unicellulare. I1 garnetofito fernminile si sviluppa second0 il tipo Polygonum e, allo stadio maturo, presenta antipodi soprannurnerarie e sinergidi con apparato filiforme. La fecondazione 5 porogarnn, I’endosperrna i: di tipo Nucleare e I’ernbriogenesi segue il tip0 Asterad.

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