Unitegmic Ovules Research Articles

Flower and fruit characters in the early‐divergent lamiid family Metteniusaceae, with particular reference to the evolution of pseudomonomery

Evaluating the morphological relationships of angiosperm families that still remain unplaced in the current systems of classification is challenging because it requires comparative data across a broad phylogenetic range. The small neotropical family Metteniusaceae was recently placed within the lamiids, as sister to either the enigmatic Oncothecaceae or the clade (Boraginaceae + Gentianales + Lamiales + Solanales + Vahliaceae). We examined the development of two of the primary diagnostic traits of Metteniusaceae, the moniliform anthers and the unilocular gynoecium. The gynoecium is 5-carpellate, and contains two ovules with a massive, vascularized integument. Late sympetaly and unitegmic ovules support placement of Metteniusaceae in the lamiids. The 5-carpellate gynoecium is consistent with a sister-group relationship between Metteniusaceae and Oncothecaceae. The gynoecium of Metteniusaceae is unusual in that it is monosymmetric throughout ontogeny, which indicates pseudomonomery; the five carpel initials are congenitally fused by their margins and form a single locule; the two ovules develop from the two smallest and most poorly developed lateral carpels. Comparisons with other pseudomonomerous taxa allow us to propose division of the complex processes leading to pseudomonomery into eight characters, including carpel number and fusion, gynoecial symmetry, timing of carpel reduction, and number and position of nonfertile carpels.

Ovule morphogenesis in Ranunculaceae and its systematic significance.

Ranunculaceae has a prominent phylogenetic position in Ranunculales which appears at the base of eudicots. The aims of the present paper are to reveal the features of ovule morphogenesis in different taxa and gain a better understanding of the systematics of Ranunculaceae. Flowers of 17 species from three subfamilies, nine tribes and 16 genera of Ranunculaceae, at successive developmental stages, were collected in the wild and studied with a scanning electron microscope. The integuments in the unitegmic ovules in Helleborus, Ranunculus and Oxygraphis, as well as the inner integuments in the bitegmic genera, initiate annularly and eventually become cup-shaped. However, the integuments in the unitegmic ovules in Anemone and Clematis, as well as the outer integuments in the bitegmic genera, arise semi-annularly and eventually become hood-shaped. Different kinds of appendages appear on the ovules during development. In Coptis of subfamily Coptidoideae, a wrap-shaped appendage arises outside the ovule and envelopes the ovule entirely. In the genera of subfamily Thalictroideae and tribe Anemoneae of subfamily Ranunculoideae, appendages appear on the placenta, the funicle or both. In tribe Helleboreae of subfamily Ranunculoideae, an alary appendage is initiated where the integument and the funicle join and becomes hood-shaped. Ovule morphogenesis characteristics are significant in classification at the levels of subfamilies and tribes. The initiation patterns of the integuments and the development of appendages show diversity in Ranunculaceae. The present observations suggest that the bitegmic, hood-shaped outer integument and endostomic micropyle are primitive while the unitegmic, cupular-shaped outer integument and bistomic micropyle are derivative.

Embryology of Siparunaceae (Laurales): characteristics and character evolution.

Embryological characters of Siparunaceae, which are poorly understood, were studied on the basis of two constituent genera, an African Glossocalyx and a South American Siparuna, to better understand their evolution within Laurales. These two genera have many embryological characteristics in common with the other lauralean families. Noticeably, they share the multi-celled ovule archesporium (uncertain in Glossocalyx) as a synapomorphy with all the other lauralean families except Lauraceae, the anthers dehisced by valves as a synspomorphy with all the other lauralean families except Calycanthaceae and Monimiaceae, and the bisporangiate anther as a synapomorphy with Gomortegaceae and Atherospermataceae. Siparunaceae are, however, distinct from all other laularean families in having unitegmic ovules that were derived from bitegmic ovules, probably due to an elimination of the outer integument. Likewise, the lack of the testa (i.e., developed outer integument), the "endotegmic" seed coat, and the perichalazal seed at maturity are also characteristics of Siparunaceae. Within the family, Siparuna differs from Glossocalyx in having plural tetrads of megaspores and plural, starchy-rich, one-nucleate, tubular embryo sacs (autapomorphies). On the other hand, Glossocalyx is characterized by having bilaterally flattened seeds (autapomorphy). Although functional aspects of those autapomorphies are uncertain, both Glossocalyx and Siparuna show evolution in different embryological characters.

Anatomy of Umkomasia (Corystospermales) from the Triassic of Antarctica

The permineralized, corystosperm, cupulate, ovule-bearing organ Umkomasia resinosa is described from the early Middle Triassic of Antarctica. This is the first description of anatomically preserved Umkomasia, which consists of a determinate cupulate branch with helically arranged, recurved, pedicellate megasporophylls, each of which bears one or two abaxially attached unitegmic ovules. Cupules are ovoid, bilobed with elongate ventral and dorsal openings or unlobed with a single ventral opening, and have a two-zoned parenchymatous cortex and abundant secretory cavities. Ovules are small, orthotropous, and possess a thin integument that contains numerous secretory cavities. The ovules are broadly attached at the base, with a bifid integumentary apex that extends past the cupule lobes. The cupulate branch displays stem-like anatomy, producing paired traces into each cupule stalk. These structurally preserved ovulate organs can be related to other corystosperm organs from Antarctica, particularly the pollen-organ Pteruchus fremouwensis. Both anatomical and morphological features support interpretation of corystosperm reproductive structures as branching systems rather than as compound sporophylls. As a result of an increased understanding of the organization of Umkomasia, it appears doubtful that any direct relationship exists between the corystosperm and angiosperm lineages.

Origins of flower morphology.

Flowers evolved in many steps, probably starting long before flowering plants (angiophytes) originated. Certain parts of flowers are conservative and have not changed much during evolution; others are evolutionarily highly plastic. Here conservative features are discussed and an attempt is made to trace them back through their evolutionary history. Microsporangia and ovules (which develop into seeds) are preangiophyte floral elements. Angiospermy, combined with postgenital fusion, was the most prominent key innovation in angiophytes. Angiospermy and thecal organization of stamens originated earlier than all clades of extant angiosperms (the crown group of angiophytes). Differentiation of a perianth into calyx and corolla and syncarpy appeared after the first branching of the basalmost clades of extant angiosperms. Sympetaly and floral tubes as well as tenuinucellar, unitegmic ovules originated as major innovations in the clade that led to asterids. An obvious trend in flower evolution is increased synorganisation of parts, which led to new structures. Fixation of floral organ number and position was a precondition for synorganization. Concomitantly, plasticity changed from number and position of organs to shape of the new structures. Character distribution mapped onto cladograms indicates that key innovations do not appear suddenly, but start with trials and only later become deeply rooted genetically in the organization. This is implied from the common occurrence of reversals in the early history of an innovation. J. Exp. Zool. (Mol. Dev. Evol.) 291:105-115, 2001.

Myrica gale L.

Deciduous, much branched shrub, 60-150 (to 250) cm in height. Main stems brown, twigs reddishbrown with scattered shiny yellowish glands, becoming dark, ascending at an angle. Young twigs downy. Roots nodulated with cluster roots; suckering habit. Buds small, ovoid, obtuse, reddish-brown, with several scales (Fl. Br. Isl.). Leaves alternate. Leaf laminae 2-6 cm long, petiole 3-5 mm long. Leaves oblanceolate or oblong-obovate in outline; subsessile. Base of blade narrowly wedge-shaped, tapering into the stalk. Margin coarsely toothed in upper third, entire below and undulate. Adaxial surface dull dark green with fine hairs. Abaxial side pale green with fine hairs on a prominent midrib. Conspicuous, scattered, shining yellowish resin glands on both surfaces. Glandular trichomes can be sessile or stalked. Stomata hypostomatous, anomocytic, venation camptodromous (leaf venation in which secondary veins bend forward and anastomose before reaching the margin of the leaf). Wood and leaves fragrant when bruised. Flowers are borne on the bare wood of the previous year's growth and appear before the leaves. Myrica gale is, for the most part, dioecious, but, within a single population, monoecious and hermaphrodite flowers may also occur (Davey & Gibson 1917), along with a skewed sex ratio of stems (Lloyd 1981). The male catkins are unbranched, usually about 10mm long with redbrown bracts, borne on leafless branches of the previous year's growth, usually in May or June. Bracteoles 0, stamens c.4, anthers red. Female catkins smaller (6-7mm), but thicker and closely set, with green bracts. The female flower is a gynoecium with 2 stigmas, 2 bracteoles, styles red and a single, basal unitegmic ovule. The ovary at pollination is superior, and very small. Following pollination, the bracts are raised up, owing to intercalary growth below the two transverse bracts, beneath the base of the gynoecium and around the locule. Thus, during fruit maturation, the ovary becomes inferior. Intercalary growth is significant in fruit wall formation. The female and male inflorescences are among the least branched of the Myricaceae, a trend that seems to correlate with an increasingly northern distribution. Fruit a nut, dry, flattened, gland-dotted, the adnate, accrescent bracteoles forming 2 wings, the exocarp secreting wax. Air-dry mass of nut (i standard error of the mean, n = 250) = 1.56 ? 0.75

The questionable relationship of Montinia (Montiniaceae): evidence from a floral ontogenetic and anatomical study

The systematic position of Montiniaceae remains uncertain: a relationship with Cornales has been suggested on phytochemical and embryological evidence, while molecular data point to a relationship with Solanales. We investigated the floral development and anatomy of the South African Montinia caryophyllacea to add a new set of characters for clarifying the systematic position of the family Montiniaceae. Pistillate inflorescences show a higher degree of reduction than staminate, with flowers set terminally on short lateral branches. Flowers have an irregular initiation sequence, with frequent abortions of organs. In Montinia, petals grow rapidly, and no zonal growth takes place. The gynoecium develops as a pit surrounded by a girdle. Placentation is basically parietal and becomes axillary by the postgenital fusion of placental lobes; unitegmic ovules are arranged in two parallel rows with adjacent ovules partly overlapping each other. Unisexuality is respectively attained at the stage of anther development and carpel initiation. The floral anatomy of pistillate and staminate flowers is illustrated and discussed. Observations on Montinia are compared with data of taxa from Saxifragaceae sensu stricto, Cornales, and Solanales. The absence of sympetaly in Montinia is discussed. Morphological and anatomical evidence points to a high similarity with Escalloniaceae. Although a position in the asterids is most probable, there is little support for the relationship with Solanales indicated by molecular data.

Phylogenetic affinities of Monimiaceae based on cpDNA gene and spacer sequences

Abstract Nucleotide sequence data from the chloroplast rbcL gene and the trnL-trnF intergenic spacer of 58 species in 38 genera were used to infer the phylogenetic affinities of Monimiaceae to other Laurales, and to assess whether the family in the traditional wide sense is monophyletic. Besides Monimiaceae, the Laurales comprise Calycanthaceae, Gomortegaceae, Hernandiaceae, and Lauraceae. Magnoliaceae and Myristicaceae were used as outgroups. Based on recent molecular data, Amborellaceae and Chloranthaceae, which have sometimes been included in the order, do not belong in the Laurales, and indeed trnL-trnF sequences of Amborella (Amborellaceae) and Hedyosmum (Chloranthaceae) were too different to be unambiguously aligned with the remaining sequences. Parsimony analyses of the trnL-trnF and trnL-trnF-rbcL data groups the genera into five major clades, Calycanthaceae, Atherospermataceae, Gomortega , Siparunaceae, and a weakly supported Monimiaceae s.str.-Lauraceae-Hernandiaceae clade. RbcL data alone provide no resolution at the family level. Many aspects of traditional intra-familiar classification of Monimiaceae are supported except that the sole perfect-flowered member of the family, the monotypic Sri Lankan Hortonia , is not basal (13 of 15–22 genera sampled). Instead, there are two major clades in Monimiaceae. One comprises the functionally dioecious monospecific Peumus from Chile plus the morphologically and functionally dioecious small genera Monimia from the Mascarenes and Palmeria from eastern Australia and New Guinea. The other consists of Hortonia and all remaining genera. The atherospermatoids are supported in their traditional circumscription (14 species, 7 genera, of which 10 and 6 were sampled). The neotropical genus Siparuna , different from recent classifications that have stressed its isolation, is genetically and morphologically very close to the West African species Glossocalyx longicuspis . Both taxa have unisexual flowers of the same general morphology, and both have unitegmic ovules. From the current data it seems that monoecy is basal in Siparuna , but more complete sampling of species with a faster evolving genetic marker is needed for a fuller understanding of the evolution of monoecy and dioecy in this genus.

Vaccinium Oxycoccos L. (Oxycoccus Palustris Pers.) and Vaccinium Microcarpum (Turcz. ex Rupr.) Schmalh. (Oxycoccus Microcarpus Turcz. ex Rupr.)

Subgenus Oxycoccus (Hill) A. Gray. Vaccinium oxycoccos L. is an evergreen shrub. Aerial stems woody, slender, flexible, terete, procumbent, prostrate, rooting, filiform, dark brown to red, occasionally up to 80 cm with short, erect or ascending flowering branches (Fl. Eur. 3; Vander Kloet 1983; Stace 1991). The leaves are (2)-5-7-(10) mm long (5 + 1.5, Vander Kloet 1983) x 2-3-(6) mm (2.0 + 0.7mm, Vander Kloet 1983), evergreen, distant, alternate, almost sessile, entire, oblong-ovate, acute, subglabrous, equally broad from some distance from the base or broader towards the middle, dark shining green above, whitish glaucous beneath with wax so thick that it frequently obscures the stomata (Vander Kloet 1983); the margin of the blade is entire, frequently revolute and often strongly so (Hegi Fl. 1, ed. 3; Fl. Eur. 3; Vander Kloet 1983; Stace 1991). Pedicels red, slender, filiform, are 2-3 cm long, more or less erect, puberulent (Fl. Br. Isl.; Stace 1991) with red scale-like bracts <1 mm wide, sometimes absent (Vander Kloet 1983); with two bracteoles, 1.5 x 0.4 mm, linear-oblong, acuminate about or below the middle (Fl. Br. Isl.; Hegi Fl. 1, ed. 3; Vander Kloet 1983). The flowers, 4-merous, are grouped in axillary or apparently terminal racemes of 1-5. The calyx lobes are deltate to semicircular and ciliate (Fl. Eur. 3) and very small (Vander Kloet 1983). The corolla, pinkishred, is divided almost to the base in lobes 5-6 mm, ovate-oblong, revolute at full anthesis and ciliate. The 8 stamens are apically dehiscent, 4-6 mm; the filaments are pubescent on the edges, glabrous or slightly pubescent outside, much shorter than anthers (Fl. Br. Isl.); the anther sacs are awnless, the tubules are slender, 1 mm long (Fl. Br. Isl.; Vander Kloet 1983); anthers are covered with small warts (Warming 1908). Pollen tetrad diameter ranges between 31.6 ,m and 47.5 ,m (Oldfield 1959; Paquereau 1959; Hegi Fl. 1, ed. 3; Hebda 1979; Vander Kloet 1983; Warner & Chinnappa 1986; Delbuscheche 1996). Style 3-4mm long, glabrous (Vander Kloet 1983). There are a mean of 20 anatropic, tenuinucellate and unitegmic ovules (Baranec et al. 1996). In Belgium, the number of ovules averages 21.6 + 6.2 per flower and the number of tetrads is about 782 + 397 per anther (Delbuscheche 1996). Hebda (1979) found a mean of 1031 (range 881-1152) tetrads per anther. Nectar is produced at the base of the style (Warming 1908). The fruit is an over-wintering berry (cranberry), globose to rarely pyriform, red (rarely white, f. leucocarpus Aschers., Hegi Fl. 1, ed. 3), sometimes speckled with white or brown, edible (Fl. Eur. 3); (4)-810-(15) mm (Fl. Eur. 3; Hegi Fl. 1, ed. 3; Grime et al. 1981; Vander Kloet 1983; Stace 1991). Seed number of berry ranges between 3 and 1 1 (Hegi Fl. 1, ed. 3; Vander Kloet 1983; Ehrlen & Eriksson 1993; Delbuscheche 1996; Eriksson & Froborg 1996): there are 14 large brown seeds in each of the 4 locules of the berry (Vander Kloet 1983). The seeds, dark brown, are 1.5-2.8 mm in length (Hegi Fl. 1, ed. 3); seed coat reticulate (Hegi Fl. 1, ed. 3). The seed fresh mass averages 0.68 + 0.17mg (n = 246) (Vander Kloet 1983). Native, on peat bogs, usually in the wetter parts (Fl. Eur. 3).

Interactions among genes regulating ovule development in Arabidopsis thaliana.

The INNER NO OUTER (INO) and AINTEGUMENTA (ANT) genes are essential for ovule integument development in Arabidopsis thaliana. Ovules of ino mutants initiate two integument primordia, but the outer integument primordium forms on the opposite side of the ovule from the normal location and undergoes no further development. The inner integument appears to develop normally, resulting in erect, unitegmic ovules that resemble those of gymnosperms. ino plants are partially fertile and produce seeds with altered surface topography, demonstrating a lineage dependence in development of the testa. ant mutations affect initiation of both integuments. The strongest of five new ant alleles we have isolated produces ovules that lack integuments and fail to complete megasporogenesis. ant mutations also affect flower development, resulting in narrow petals and the absence of one or both lateral stamens. Characterization of double mutants between ant, ino and other mutations affecting ovule development has enabled the construction of a model for genetic control of ovule development. This model proposes parallel independent regulatory pathways for a number of aspects of this process, a dependence on the presence of an inner integument for development of the embryo sac, and the existence of additional genes regulating ovule development.

The character states of Mussaendopsis Baill. (Rubiaceae-Coptosapelteae)

Summary Mussaendopsis, an arborescent Southeast Asiatic genus of two species (M. beccariana: from the Malay Peninsula and Sumatra East to Borneo; M. celebica: endemic to Sulawesi) has mature stipules in an intrapetiolar position. Developmental studies on M. beccariana, however, showed that they are initially interpetiolar. The large coriaceous leaves, characterized by the presence of two hypodermis layers, have conspicuous sclerenchymatic bundle sheath extensions. The optical attractiveness of the (pleio-)thyrsic or thyrsopaniculate, axillary inflorescences is markedly increased by the presence of enlarged, petaloid, show calyx lobes which are produced only by certain flowers of an inflorescence (± pseudanthium-like). The corollas (corolla lobe aestivation contorted to the right in bud) differ significantly in the two species: In M. celebica, they are hypocrateriform (corolla tubes c. 3.5 mm long; tubes always shorter than the lobes) and in M. beccariana, they are rotate (tube subobsolete to obsolete). The latter, suspected to be myophilous (“dishblossom”, large, exposed ± flat disk profusely producing nectar), shows dichogamy (protandry) coupled with herkogamy. The ovary of the bicarpellate gynoecium contains two large placentas, each with numerous hemianatropous, tenuinucellate and unitegmic ovules which are produced in a sequential fashion. In the course of flower and fruit development, ovules and developing seeds undergo a drastic change in shape: ovules soon develop a winglike extension (marked elongation of the chalazal region!), resulting in a distinctly imbricate arrangement of the tightly packed, variably shaped ovules. Further on, the wing-like outgrowths also encompass the micropylar end of the ovules so that, finally, the mature seeds show an elongated, bipolar wing which surrounds the ± centrally located endosperm- and embryo-bearing part on all sides. The exotesta cells have conspicuous anastomosing local secondary thickenings on the inner tangential walls only. The distinctly oily endosperm consists only of a few cell layers surrounding the relatively large embryo. The fruits are septicidal capsules with hard walls (thick, sclerenchymatic endocarp). The pollen of M. beccariana, 3-colporate and ± spheroidal (P = ± E = 18 – 19.8 μm), has a reticulate to finely reticulate exine. The presented data do not seem to seriously contradict the recently suggested placement of Mussaendopsis in the tribe Coptosapelteae, although they might suggest a ± isolated position of the genus in this essentially paleo tropical tribe.

Floral anatomy of the Styracaceae, including observations on intra-ovarian trichomes

Abstract All eleven genera of the Styracaceae were examined with respect to floral morphology and anatomy. Floral structure and vascularization are described in detail. Flowers of the family exhibit different degrees and patterns of specialization. All Styracaceae show some degree of basal non-divergence of perianth members, forming a hypanthium that is adnate to the ovary wall to a lesser or greater extent. The extent of reduction and amplification in the number of sepals, petals, stamens, and carpels varies widely among genera, and generally the non-divergence, decrease, or increase in parts is not equally pronounced in the different whorls of the same sower. Genera cannot be readily aligned in an intergrading sequence of morphological advancement. Stamen form and anatomy is variable. A fibrous endothecium ranges from well-developed to weakly formed or absent. A nearly uniform feature of the styracaceous gynoccium is the presence of incompletely septate ovaries. The major points of variation in the floral vascular system relate to the number, mode of origin, and degree of independence of sepallary traces; degree of independence of the androecial vasculature; the level at which the common petal and petaladstamen or sepal and sepalad-stamen bundles separate to their component parts; organization of the ventral ovarian supply; and the occurrence of ventral bundles in the style. Floral vascularization provides evidence that the family was derived from an obdiplostemonous ancestor. A unitegmic ovule is predominant in the family and starch is present in the megagametophyte of some taxa. An unusual feature of the flowers of the Styracaceae is the occurrence of stellate and lignified intraovarian trichomes. Numerous similarities in floral morphology and anatomy between Styracaceae and Ericales are pointed out.

Floral anatomy of the Styracaceae, including observations on intra-ovarian trichomes

All eleven genera of the Styracaceae were examined with respect to floral morphology and anatomy. Floral structure and vascularization are described in detail. Flowers of the family exhibit different degrees and patterns of specialization. All Styracaceae show some degree of basal non-divergence of perianth members, forming a hypanthium that is adnate to the ovary wall to a lesser or greater extent. The extent of reduction and amplification in the number of sepals, petals, stamens, and carpels varies widely among genera, and generally the non-divergence, decrease, or increase in parts is not equally pronounced in the different whorls of the same ßower. Genera cannot be readily aligned in an intergrading sequence of morphological advancement. Stamen form and anatomy is variable. A fibrous endothecium ranges from well-developed to weakly formed or absent. A nearly uniform feature of the styracaceous gynoccium is the presence of incompletely septate ovaries. The major points of variation in the floral vascular system relate to the number, mode of origin, and degree of independence of sepallary traces; degree of independence of the androecial vasculature; the level at which the common petal and petaladstamen or sepal and sepalad-stamen bundles separate to their component parts; organization of the ventral ovarian supply; and the occurrence of ventral bundles in the style. Floral vascularization provides evidence that the family was derived from an obdiplostemonous ancestor. A unitegmic ovule is predominant in the family and starch is present in the megagametophyte of some taxa. An unusual feature of the flowers of the Styracaceae is the occurrence of stellate and lignified intraovarian trichomes. Numerous similarities in floral morphology and anatomy between Styracaceae and Ericales are pointed out.

PATTERNS OF EMBRYO AND ENDOSPERM FORMATION IN MONOTROPA HYPOPITYS (MONOTROPACEAE) FROM NORTH AMERICA AND WESTERN SWEDEN

Within the Monotropaceae, Monotropa hypopitys L. has the widest geographical distribution with sporophytes characterized as achlorophyllous, mycotrophic, and morphologically reduced. General and histochemical observations at the light microscope level concerning the postpollination changes in the numerous anatropous, unitegmic ovules reveal a precise embryogeny and endosperm development. Following double fertilization, the primary endosperm cell produces a lipid-rich cellular endosperm situated between a micropylar and a chalazal haustorium. A cytoplasmically unequal division of the elongated zygote initiates proembryo formation. The degeneration of the basal cell of the proembryo results in an isolated terminal cell that undergoes a cytoplasmically equal, transverse division establishing a two-celled embryo embedded in endosperm. Prior to final seed maturation, proteins replace the lipids as the dominant cytoplasmic reserve material. In contrast with earlier studies that depicted the mature embryo as variable in structure, here the embryo is shown to be consistently uniform within and between those populations sampled from North America and Europe. Although often classified as a subfamily of the Erica

The histogenesis of integuments in some species of menispermanceae

The mode of initiation and development of integuments was investigated in six species of five genera in Menispermanceae, which have bitegmic and unitegmic ovules. The species investigated have similar integumentary structures at maturity in each of the bitegmic and unitegmic ovules. In bitegmic ovules (e.g.Cocculus), both integuments are for the most part two-cell layered. The initiation of inner integument (ii) begins with divisions of dermal cells of the nucellar primordium. The initiation of the outer integument (oi) commences with divisions of subdermal cells. In unitegmic ovules (e.g.Stephania), the integument is initiated by periclinal divisions of dermal cells, and cells of subdermal origin (which may represent the oi in case of bitegmy) form a small swelling on the raphal side and, on the antiraphal side, are included in the base of the single integument. Unitegmy of Menispermanceae (at least in the case of the genera investigated) seems to have been derived through elimination of oi, rather than through “integumentary shifting” (Bouman and Calis, 1977), a process suggested for explanation of unitegmy as in Ranunculaceae.

POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF HOPLESTIGMATACEAE

SummaryThe pollen of the ditypic family Hoplestigmataceae was examined in LM, SEM, and TEM, and in conjunction with floral morphology compared with the orders Boraginales, Ebenales, and Violales, to which this family has been assigned. Hoplestigma has pollen with 3‐colporate apertures bordered by (six) meridional ridges that are separated by (three) intercolpar concavities. Pollen similar in SEM and TEM is found in Bourreria and Ehretia of the Boraginaceae, and is also common in the Myrtales. However, this pollen type is not known to occur in either the Violales or Ebenales; in addition the bicarpellate ovary with few ovules and sympetalous corolla of Hoplestigma are not really typical of the Violales, nor is the parietal placentation of Hoplestigma typical of the Ebenales. Although Hoplestigma shares similar pollen, numerous stamens, and many characteristics of the gynoecium with the Myrtales, it differs in having the petals united basally and unitegmic ovules versus distinct petals and bitegmic ovules in Myrtales. Until Hoplestigmataceae is examined for the presence of internal phloem, one of the more definitive characters for Myrtales, we defer to Takhtajan's placement in the Boraginales.

Fruit Development and Structure in Some Indian Bamboos

Fruit structure and development of seven species belonging to five genera of Indian bamboos are described. The fruit in four species is a caryopsis typical of the family Poaceae. The ovule is bitegmic; the outer surface of the cells of nucellar epidermis becomes cutinized and forms the seed coat. Three species bear a fleshy fruit with a unitegmic ovule. In a mature fruit the endosperm is either completely absorbed by the embryo or is present only in small quantity. The developing embryo comes in direct contact with the fruit wall due to the disintegration of the nucellus and integument. The embryo is covered by a thick brown mat from the disorganized cells of the inner layers of the fruit wall.

Shoot development in Betula papyrifera. VI. Development of the reproductive structures

Reproductive buds and developing inflorescences were collected weekly from mature trees during three successive growing seasons in northwestern Ontario. Material was prepared to show all stages of inflorescence and flower development and meiosis. Male inflorescence induction, involving the long-shoot bud apex and one or two proximal axillary apices, occurred in early May, before bud burst. Female induction involved the short-shoot bud apex and occurred in late June – early July. Both male and female partial inflorescences resembled a simple dichasium. The male flower consisted of usually two stamens and two or three tepals variably arranged. Meiosis occurred in late July – early August. Each female flower consisted of two stigmas, two connate tepals that were not noticeable at maturity, and a parietal placenta bearing two unitegmic ovules. Meiosis occurred in mid-June, after pollination in mid-May. It is concluded that developmental data do not help elucidate whether the inferior portion of the gynoecial wall is cauline or appendicular and whether the placenta is derived from axial or carpellary tissue. It is suggested that the trigger(s) evoking male and female inflorescence induction may be different and that the metabolic prerequisites for induction and early development would be supplied by winter-stored material for male development and by current metabolic processes for female development.

Studies in Gentianaceae. Embryology of Swertia minor (Gentianinae)

The embryology of Swertia minor Knobl. (Gentianinae Gentianaceae) was studied. Features of its development are tetrasporangiate anthers, dicotyledonous type sporangial wall formation, glandular anther tapetum and its dual origin, simultaneous cytokinesis in microsporocytes, tricolporate two-celled pollen, unilocular ovary, forked parietal placentae, tenuinucellar unitegmic anatropous ovules, Polygonum-type megagametogenesis, persistent multiple multinucleate highly enlarged haustorial antipodal cells, nuclear endosperm, Solanad type embryo development, and multiseriate suspensor. Embryological features of taxonomic significance in the Gentianinae are compiled in a review of the pertinent data on the subtribe.

INTEGUMENTARY STUDIES IN THE POLYCARPICAE V. NIGELLA DAMASCENA L.

SUMMARY The ovule primordium of Nigella damascena is three-zonate. The nucellus of most ovules is crassinucellate. The inner integument is of dermal origin, whereas the outer integument is initiated subdermally. These ovule characteristics correspond with those of the supposedly most original type of the angiospermous ovule. The ovule can be used as a base of comparison with unitegmic ranunculaceous ovules and with ovules showing a structure intermediate between bi- and unitegmy.