Ultrastructure of the tapetal cell wall in the stamenless-2 mutant of tomato (Lycopersicon esculentum): correlation between structure and male-sterility

Summary In the stamenless-2 (sl-2) mutant of tomato (Lycopersicon esculentum Mill.), the breakdown in microsporogenesis corresponded with various abnormalities in the ultrastructure of the tapetal cell wall. In some mutant anthers, the inner tangential wall was excessively loosened allowing the passage of tapetal cell wall material and cytoplasmic contents into the anther locule. This presumably altered the osmoticum of the locule and resulted in plasmolysis of the microspores. Membranous fragments commonly observed in the normal tapetal cell wall, and presumed to have a role in transfer of materials from the tapetum to microspores, were absent from thesl-2 mutant. This was associated with reduced transfer of materials, such as lipids, to the developing pollen grains. In addition, a lining of sporopollenin-like deposits that coated the inner tangential wall of the normal tapetum, was discontinuous in the mutant. In mutant anthers where the tapetal cell wall did not loosen, the transfer of all materials was restricted and this resulted in the collapse of sporogenous material.     

GYNOECIAL ONTOGENY AND MORPHOLOGY,AND POLLEN TUBE PATHWAY IN BLACK MAPLE,ACER SACCHARUM SSP. NIGRUM (ACERACEAE)

The black maple (Acer saccharum Marsh, ssp. nigrum [Michx. f.] Desm.) gynoecium displays classical involute carpel development; carpels form, in mid- to late-summer, as two separate, opposite, hood-shaped primordia bearing naked megasporangia on inrolled carpel margins. Megasporogenesis, integument initiation, and carpel closure occur in spring; carpels fuse, forming a biloculate ovary with a short, hollow style and two divergent, dry, unicellular papillose stigmas. Transmitting tissues consist of developmentally and morphologically similar trichomes that form along the apparent carpel margins. The path from stigma to micropyle is open, but pollen tubes do not grow entirely ectotrophically. Germinating at the tip of a stigma papilla, a tube grows, apparently under the cuticle, to the papilla base. It then grows between stigma cells to the style, emerging to grow ectotrophically through the style to the compitum, where it passes into one of the locules. Within a locule, the tube grows over placenta and obturator to the micropyle, then between megasporangium cells to the female gametophyte, spreading over the surface near the egg. This study adds to our sparse understanding of gynoecium development and transmitting tissue in relation to pollen tube growth in naturally pollinated woody plants.     

Is the quantity of orbicules released by Dactylis glomerata and Cynosurus echinatus (Poaceae) big enough to play an allergenic role?

Orbicule characteristics of Dactylis glomerata and Cynosurus echinatus (Poaceae) were investigated using light (LM), scanning electron (SEM) and transmission electron microscopy (TEM). Based on SEM micrographs, the number of orbicules per 100?µm² of the locule wall surface was determined in both dehisced and undehisced anthers and was further compared statistically. A total of 100 pollen grains were examined using SEM in search for orbicules attached to the pollen exine. Orbicules were not found distributed freely in the anther locules. They were attached to the locule wall surface through sporopolleninous fibrils, the orbicule wall being firmly embedded in, and often in continuity with the thin layer of sporopollenin lining each locule. The orbicule density on the locule wall surface of both the dehisced and undehisced anthers did not differ significantly. Only a few orbicules were seen attached to the pollen exine in both species. It is concluded that orbicules are not easily removed from the surface of the locule wall and, consequently, that the number of orbicules emitted from the two grass species is too low to play a significant role in triggering allergic diseases.     

THE MORPHOLOGY OF THE MYRISTICACEAE. I. FLOWERS OF MYRISTICA FRAGRANS AND M. MALABARICA

Floral histology and vascular anatomy of Myristica fragrans Van Houtt. and M. malabarica Lam. have been investigated from serial sections and specimens cleared in chloro-lacto-phenol. The flowers are unisexual. The androecium is considered to consist of a whorl of laterally concrescent anthers. The bisporangiate anthers are attached by a ridge of tissue to the terminal part of the androphore. In many cases the number of vascular bundles in the androphore is half the number of anthers. The gynoecium consists of a monocarpellate pistil with basal placentation and a single anatropous ovule. Of the many vascular bundles that enter the base of the carpel, two, because of their position and because they provide vascular traces to the ovule, are designated as ventral bundles. Additional ovular traces are provided by the carpel wall vascular system. These additional traces originate at the top of the locule and descend to the ovule. The similarity between the androecia of these two species and the androecium of the ćnellaceae is noted.     

DIOECY IN BAUHINIA RESULTING FROM ORGAN SUPPRESSION

Bauhinia malabarica and B. divaricata have both been reported to have dimorphic flowers; floral development of these species has been investigated and compared using SEM. B. malabarica is subdioecious, with three types of flowers: perfect, staminate, and carpellate. Individual trees usually have only one type of flower. Perfect and carpellate flowers have similar initiation of floral organs; each has five sepals, five petals, two whorls of five stamen primordia and a carpel primordium. The carpels of carpellate flowers do not differ from those of perfect flowers throughout development. Both have a gynophore or stipe and a cuplike hypanthium. Stamen development diverges markedly after mid-development: the perfect flowers have ten stamens in two whorls, the outer with longer filaments than the inner. All stamens have anthers, which are covered abaxially with abundant inflated trichomes. Carpellate flowers have a circle of short cylindrical staminodia, each bearing a few hairs, about the base of the carpel on the rim of the hypanthium. Heteromorphy in B. malabarica is effected by suppression of stamen development, even though the usual number of stamen primordia is initiated. Suppression of stamens occurs at midstage in development in carpellate flowers of B. malabarica, and is complete. In B. divaricata nine stamen primordia are released from suppression in late stage, undergo intercalary growth and form a staminodial tube around the carpel stipe. The dimorphy in B. divaricata is expressed late in bud enlargement as divergent rates of growth in the carpel in the two morphs.     

Comparative floral ontogenies among Persoonioideae including Bellendena (Proteaceae)

Floral ontogeny is described and compared in five species and four genera of the hypothetically basal proteaceous subfamily Persoonioideae sensu Johnson and Briggs. The hypotheses surrounding the origin of the peculiar proteaceous flower and homologous structures within the flowers are examined using ontogenetic morphological techniques. Ontogenetic evidence reveals that the proteaceous flower is simple, composed of four tepals, each tepal initiated successively with the lateral tepals being initiated first and second followed by the successive initiation of the sagittal tepals. Each of four stamens is initiated opposite a tepal in a similar sequence to tepal initiation. A single carpel develops terminally from the remaining floral meristem. In taxa of Persoonieae, nectaries are initiated from a broadened receptacle in alternistamenous sites after zonal growth beneath and between the tepals and stamens has begun. The nectaries are interpreted as secondary organs, not reduced homologues of a “lost” petal or stamen series. Developmental variation is present among the examined taxa in several forms including the development of a Vorlaüferspitze (spine) on the upper portion of the tepals, adnation between the anthers and tepals, and formation of the carpel. In Placospermum the early formation of the carpel cleft extends to the floral receptacle and in the other taxa, the carpel cleft is distinctly above the receptacle. Different developmental pathways result in similar mature morphologies of the carpel in Persoonia falcata and Placospermum coriaceum. Bellendena montana is unique relative to the other taxa in having free stamens, a punctate stigma, reduced (not lost) floral bracts, and the floral and bract primordia are initiated from a common meristem. This study provides a foundation for future studies of the developmental basis of floral diversity within Proteaceae.     

SECRETORY CAVITY DEVELOPMENT IN GLANDULAR TRICHOMES OF CANNABIS SATIVA L. (CANNABACEAE)

Development of the secretory cavity and formation of the subcuticular wall of glandular trichomes in Cannabis sativa L. was examined by transmission electron microscopy. The secretory cavity originated at the wall-cuticle interface in the peripheral wall of the discoid secretory cells. During the presecretory phase in development of the glandular trichome, the peripheral wall of the disc cells became laminated into a dense inner zone adjacent to the plasma membrane and a less dense outer zone subjacent to the cuticle. Loosening of wall matrix in the outer zone initiated a secretory cavity among fibrous wall materials. Membrane-bound hyaline areas, compressed in shape, arose in the wall matrix. They appeared first in the outer and subsequently in the inner zone of the wall. The membrane of the vesicles, and associated dense particles attached to the membrane, arose from the wall matrix. Hyaline areas, often with a conspicuous electron-dense content, were released into the secretory cavity where they formed rounded secretory vesicles. Fibrous wall material released from the surface of the disc cells became distributed throughout the secretory cavity among the numerous secretory vesicles. This wall material was incorporated into the developing subcuticular wall that increased five-fold in thickness during enlargement of the secretory cavity. The presence of a subcuticular wall in the cavity of Cannabis trichomes, as contrasted to the absence of this wall in described trichomes of other plants, supports a polyphyletic interpretation of the evolution of the secretory cavity in glandular trichomes among angiosperms.     

An ultrastructural and cytochemical study of the wall-membrane apparatus of transfer cells using freeze-substitution

Summary A freeze-substitution technique is described which enables the ultrastructure of certain types of plant transfer cells to be preserved with minimal ice crystal damage. The ultrastructure of transfer cells fromFunaria, Lonicera, andSenecio after freeze-substitution has been compared with that of glutaraldehyde-osmium fixed material. The irregular clear zone between wall and plasma membrane, present in conventional preparations, is absent in freeze-substituted tissue. It is proposed that this interfacial zone is an artefact caused by expansion of wall ingrowth material during conventional fixation procedures. In transfer cells with a complex wall labyrinth the swelling of wall material severely disrupts the true structure of the wall-membrane apparatus and results in a large decrease in the surface to volume ratio of the protoplast. These findings are supported in the case ofFunaria by a freezefracture study. The reactivity of the plasma-membrane to the PTA/chromic acid stain is enhanced in freeze-substituted material. Use of theThiéry silver proteinate reagent in conjunction with freeze-substitution has revealed marked differences between the wall ingrowths ofFunaria sporophyte haustorium transfer cells and those ofLonicera nectary trichomes.     

Developmental Ultrastructure of Glandular Trichomes of <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>: Secretory Cavity and Secretory Vesicle Formation

Glandular trichomes in the leaf lamina of Rosmarinus officinalis L. were examined by scanning and transmission electron microscopy. The leaves were characterized by an abundance of two types of glandular trichomes—small capitate and large peltate glandular trichomes. In addition to the glandular trichomes, numerous non-glandular trichomes were present on the abaxial surface of the leaf. These trichomes mainly predominated on the midrib, whereas glandular trichomes occurred on non-vein areas. At the initial phase of secretory cavity formation, hyaline areas were abundant in periclinal walls of head cells, while they were not observed in the anticlinal walls. The hyaline areas gradually increased in size, fusing with other areas throughout the wall. Loose wall material adjacent to hyaline areas was released from the head cell walls and migrated into the secretory cavities. As the secretory cavities continued to enlarge, the new vesicles emerging into the secretory cavities from the walls of head cells became surrounded with the surface of a typical membrane. They developed a round shape, but the contours of the vesicle surfaces appeared polygonal when tightly packed inside a cavity. These vesicles varied in size; small vesicles often possessed electron-dense contents, while large vesicles contained electron-light contents.     

ORIGIN AND DEVELOPMENT OF THE TERMINAL CARPEL IN PSEUDOWINTERA TRAVERSII

Flowers of Pseudowintera traversii (Buchan.) Dandy possess a terminal unicarpellate gynoecium. The present study of carpel morphogenesis was initiated for the purposes of (1) providing additional developmental documentation of the occurrence of terminal carpels in the Winteraceae and (2) comparing the mode of initiation and development of the ascidiate terminal carpel of P. traversii with the essentially conduplicate terminal carpel of Drimys lanceolata. Following its axillary origin, the floral apex of P. traversii initiates 2–3 connate sepals, 5–6 petals, 4–15 stamens, and usually a single terminal carpel, in acropetal succession. Bicarpellate gynoecia may occur with a frequency of up to 15 % on a given plant. The floral apex is zonate and shows increased expression of its zonation during later stages of floral development. The terminal carpel is ascidiate from inception and originates as a cylindrical growth around the entire circumference of the floral apex; transformation of the floral meristem into a carpel primordium terminates apical growth of the floral axis. Carpel growth continues to be cylindrical and is mediated by a ring of marginal and submarginal initials at its summit. Earlier and more extensive division of initials and their derivatives on the dorsal rim causes the primordium to become canted adaxially, shifting the apical cleft to a subterminal adaxial position. Continued marginal meristematic activity results in closure of the cleft as well as elevation and elaboration of the stigmatic crests. Five to seven bitegmic ovules are initiated at the same time as crest elaboration and arise in two rows from the adaxial (laminar) position. Carpel maturation is signified by tannin deposition and oil cell differentiation, beginning at the base and proceeding acropetally; carpel margins bordering the cleft are the last to differentiate. Carpel procambialization is continuous and acropetal from inception, with the dorsal median bundle differentiating before the ventral strands. The significance of occasional bicarpellate flowers is discussed.     

THE DEVELOPMENTAL BASIS FOR SEXUAL EXPRESSION IN CERATONIA SILIQUA (LEGUMINOSAE: CAESALPINIOIDEAE: CASSIEAE)

The flowers of Ceratonia siliqua, an anomalous caesalpinioid legume in the tribe Cassieae, are unusual in being unisexual and in lacking petals. Inflorescence development, organogeny, and flower development are described for this species. All flowers are originally bisexual, but one sex is suppressed during late development of functionally male and female flowers. Ceratonia siliqua is highly plastic in sexuality of individuals, inflorescence branching pattern, racemose or cymose inflorescences, bracteole presence, terminal flower presence, organ number per whorl, missing floral organs, pollen grain form, and carpel cleft orientation. Order of initiation is: five sepals in helical order, then five stamens in helical order together with the carpel. Each stamen is initiated as two alternisepalous primordia that fuse to become a continuous antesepalous ridge; in some flowers, the last one or two stamens of the five may form as individual antesepalous mounds. Petal rudiments are occasional in mature flowers. Position of organs is atypical: the median sepal is on the adaxial side in Ceratonia, rather than abaxial as in most other caesalpinioids. This feature in Ceratonia may be viewed as a link to subfamily Mimosoideae, in which this character state is constant.     

PISTIL DEVELOPMENT AND PARIETAL PLACENTATION IN THE PSEUDOMONOMEROUS OVARY OF ZELKOVA SERRATA (ULMACEAE)

Development of female flowers in Zelkova serrata was observed using epi-illuminated microscopy and scanning electron microscopy, with particular attention given to placentation. After the inception of staminodial primordia, the floral apex becomes flat, and the first and subsequently the second carpel primordia appear at opposite comers of the pistil primordium. Inside each carpel primordium a fossette forms. Through differential growth this depression becomes clear and the carpel wall encircles one side of the future placental region. The placental region is detectable even in early stages, but clear signs of ovule inception appear late when the placental region is elevated onto one side of the ovary wall by intercalary growth. Although the relative size of the two carpels varies among flowers, the placental position always appears to be the border between the two carpels and the floral apex. This suggests that the placentation of Zelkova is parietal. The ovule position in tricarpellate ovaries also suggests an evolutionary derivation from ovaries with parietal placentation. Parietal placentation appears to be the original condition in Urticales.     

CARPEL DEVELOPMENT IN DRIMYS LANCEOLATA

The dissimilar carpels of representatives of the Tasmannia and Wintera sections of the genus Drimys have been investigated developmentally with particular attention to the presence of peltation. In Drimys winteri of the Wintera section peltation results from an active adaxial meristem, but in D. lanceolata of the Tasmannia section the adaxial “cross-zone” meristem is weakly developed and contributes little to the carpel. The form of the carpels also shows contrasts; the carpel of D. lanceolata begins growth as paired ridges separated by a cleft extending over the summit. Allometric growth reorients the cleft and it eventually extends from the ventral base of the carpel up over the summit. The cleft elongates greatly, together with the main part of the carpel. In D. winteri, growth is concentrated below the level of the cleft, and the carpel grows as an elongating cylinder. The cleft remains short, not extending with the carpel. In both species, early growth involves subsurface initials: subapical, adaxial (although weak in D. lanceolata), and submarginal. The presence of a disc encircling the base of the solitary carpel is reported for the first time for D. lanceolata.     

STUDIES ON THE FLORAL ANATOMY OF THE CUNONIACEAE

Twenty-two genera representing sixty-two species of Cunoniaceae and Davidsonia were examined with respect to floral anatomy. Sepals are vascularized by three traces with the lateral traces of adjacent sepals united. Pancheria is unique for the family with species in which the sepals are vascularized by a single, undivided bundle. Petals, when present, and stamens, are uniformly one-trace structures. A general tendency exists within the family for the principal floral bundles to unite in various ways, with fusions evident between calyx, corolla, and androecial vascular supplies. Carpel number ranges from two to five and the gynoecium is generally surrounded by a prominent disc. Gynoecia of Ceratopetalum and Pullea are “half-inferior.” The number of ovules per carpel locule ranges from one to numerous. Ventral carpel sutures range from open to completely sealed at the level of placentation. Carpels of the apocarpous genus Spiraeanthemum (incl. Acsmithia) are vascularized by a dorsal bundle and either three or four bundles constituting the ovular and wing vasculation in the ventral position, a condition unlike other members of the family. Ovules are supplied by the median ventral bundle. More advanced bicarpellate gynoecia within the family are predominately vascularized by a dorsal and two ventral bundles although a variable number of additional lateral wall traces may be present. A major trend exists toward fusion of the ventral bundles of adjacent carpels in the ovary of both bicarpellate and multicarpellate plants. At the base of the styles the fused ventral strands separate and extend along with the dorsal carpellary bundles into styles of adjacent carpels. In Pullea the ventral bundles terminate within the ovules. The united ventral carpellary bundles in Aphanopetalum, Gillbeea, and Aistopetalum lie in the plane of the septa separating adjacent carpels. Ovules are vascularized by traces originating from the vascular cylinder at the base of the gynoecium or by traces branching from the ventral bundles. Ovular traces in each carpel are united, or remain as discrete bundles, prior to entering the placenta. Tannin and druses are common throughout all floral parts. Although floral anatomy generally supports the position of Cunoniaceae near Saxifragaceae and Davidsoniaceae, the evolutionary relationship of the Cunoniaceae to the Dilleniaceae is uncertain.     

RE-EVALUATION OF CERTAIN KEY RELATIONSHIPS IN THE ALISMATIDAE: FLORAL ORGANOGENESIS OF SCHEUCHZERIA PALUSTRIS (SCHEUCHZERIACEAE)

Transition to flowering in the North-temperate bog plant Scheuchzeria palustris occurs in early May and results in the formation of a simple raceme with six flowers. Five of the flowers are subtended by large foliar bracts, while the sixth and last-formed flower on the inflorescence remains ebracteate. The individual flowers develop along a clearly trimerous pattern. The three outer tepals develop first, arising almost simultaneously at the periphery of the triangular floral apex. They are followed closely by the development of the three anti-tepalous outer stamens. The three inner tepals are next in the developmental sequence, alternating with the outer whorl of tepal-stamen pairs but arising at a slightly higher level on the floral meristem. Three inner stamens are initiated opposite the inner tepal primordia. Finally, three gynoecial primordia are initiated on the remaining central portion of the floral apex and alternating with the inner whorl of tepal-stamen pairs. Each carpel develops at first as a horseshoe-shaped structure. Two ovules form in each carpel, initiating on the adaxial margin of the carpel wall. Histogenesis of all floral appendages involves initially periclinal divisions in the second tunica layer followed by corresponding anticlinal divisions in the first tunica layer and concurrent activity in the underlying corpus. Separate procambial strands differentiate acropetally from the inflorescence axis to each tepal-stamen pair and then bifurcate. The vascular connection to the gynoecium develops directly from the strands in the tepal-stamen pairs. The results of this developmental study of the flower of S. palustris have a significant bearing on the positioning of this and related taxa within the Alismatidae and on the speculation of the phylogeny of the monocotyledon flower.     

FLORAL ANATOMY IN THE SAXIFRAGACEAE SENSU LATO. II. SAXIFRAGOIDEAE AND ITEOIDEAE

The floral anatomy and morphology of 26 species from the Saxifragoideae and three from the Iteoideae are described and compared. The flowers of the Saxifragoideae are predominantly actinomorphic, partially epigynous and/or perigynous, and pentamerous, with two carpels which bear numerous ovules. There is usually some degree of independence between carpels, and the normally separate styles possess both a canal and transmitting tissue. Generally, staminodia are absent and nectariferous tissue, which is not vascularized, is present. The subfamily is characterized by large multicellular trichomes with globular, often glandular, heads. Placentation may be parietal, axile, or transitional between the two; parietal appears to be a derived condition in the subfamily. The vascular cylinder in the pedicel generally consists of several to many discrete bundles from which diverge ten compound traces at the base of the receptacle, leaving an inner cylinder of vascular strands that coalesce at a higher level into either as many ventral bundles as carpels or twice that number. In the former case, each ventral bundle consists of one-half of the vascular supply to each adjacent carpel and separates into individual ventral strands in the distal half of the ovary. The ventral bundles provide vascular traces to the ovules and, along with the dorsals, extend up the style to the stigma. Each trace diverging in a sepal plane typically supplies one or more carpel-wall bundles, a median sepal bundle, and a stamen bundle. Each petal-plane trace usually provides one or more carpel-wall bundles, a lateral trace to each adjacent sepal, a petal bundle and, in flowers with ten stamens, a stamen bundle. Dorsal carpel bundles are usually recognizable and may originate from traces in either perianth plane. While the position of Ribes remains problematical, its floral structure does not easily exclude it from the Saxifragoideae. Floral structure in the Iteoideae is remarkably similar to that in the Saxifragoideae, the main differences being a lesser degree of independence between carpels, generally narrower placentae with somewhat fewer ovules, and the presence of only unicellular, acutely pointed epidermal hairs as opposed to the relatively complex, multicellular trichomes prevalent in the Saxifragoideae.     

黄瓜雄花形成过程中心皮的发育

黄瓜(Cucumis sativus L.)为重要的经济作物,雌雄同株异花,是研究植物性别分化的经典材料。人们对黄瓜性别分化进行了广泛的研究。Astmon和Galun、任吉君和王艳对黄瓜性别分化的形态特征和器官发生进行了初步研究,表明黄瓜单性花分化和发育过程中经历了无性期、两性期和单性期,最终只有一种性别的性器官原基发育成有功能的性器官,从而形成单性花,而对单性花中未形成有功能器官的相反性别原基的研究报道甚少。我们对雄花发育过程进行了连续的形态学分析,并对不同时期雄花中的心皮进行了细胞计数和同工酶电泳分析,以期从性器官发育的角度探讨黄瓜性别表现的机理。     

NORMAL FLORAL ONTOGENY AND COOL TEMPERATURE-INDUCED ABERRANT FLORAL DEVELOPMENT IN GLYCINE MAX (FABACEAE)

Floral onset in soybean (Glycine max cv. Ransom) is characterized by precocious initiation of axillary meristems in the axils of the most recently initiated leaf primordium. During floral transition, leaf morphology changes from trifoliolate leaf with stipules, to a three-lobed bract, to an unlobed bract. Soybean flowers initiated at 26/22 C day/night temperatures are normal, papilionaceous, and pentamerous. Sepal, petal, and stamen whorls are initiated unidirectionally from the abaxial to adaxial side of the floral apex. The median sepal is located abaxially and the median petal adaxially on the meristem. The organogeny of ‘Ransom’ flowers was found to be: sepals, petals, outer stamens plus carpel, inner stamens; or, sepals, petals, carpel, outer stamens, inner stamens. The outer stamen whorl and the carpel show possible overlap in time of initiation. Equalization of organ size occurs only within the stamen whorls. The sepals retain distinction in size, and the petals exhibit an inverse size to age relationship. The keel petals postgenitally fuse along part of their abaxial margins; their bases, however, remain free. Soybean flowers initiated at cool day/night temperatures of 18/14 C exhibited abnormalities and intermediate organs in all whorls. The gynoecium consisted of one to ten carpels (usually three or four), and carpel connation varied. Fusion of keel petals was often lacking, and stamen filaments fused erratically. Multiple carpellate flowers developed into multiple pods that were separate or variously connate. Intermediate type organs had characteristics only of organs in adjacent whorls. These aberrant flowers demonstrate that the floral meristem of soybean is not fixed or limited in its developmental capabilities and that it has the potential to produce alternate morphological patterns.     

Ultrastructure of the Water-absorbing Trichomes of Pineapple (Ananas comosus, Bromeliaceae)

An ultrastructural study of dry and wet trichomes from the upperleaf surface of pineapple revealed that shield cells were normallydead and stalk cells were often living. In stalk cells of drytrichomes, polysaccharide material was present within vacuolesand a layered material was present between the plasma membraneand cell wall. In stalk cells of trichomes wet for 12 h vacuoleswere enlarged and appeared to contain little material. Layeredmaterial between the plasma membrane and cell wall was alsoabsent. In both wet and dry trichomes, numerous mitochondriawere present and plasmodesmata were observed connecting stalk,foot, and adjacent epidermal and mesophyll cells. It is suggestedthat the large numbers of mitochondria, which indicate highmetabolism, and the numerous plasmodesmata connecting the cells,provide indirect evidence for the function of the trichomesin uptake of dissolved nutrients. Ananas comosus (L.) Merr., pineapple, trichomes, ultrastructure, Bromeliaceae     

FLORAL DEVELOPMENT IN MYRISTICA (MYRISTICACEAE)

Myristica fragrans and M. malabarica are dioecious. Both staminate and pistillate plants produce axillary flowering structures. Each pistillate flower is solitary, borne terminally on a short, second-order shoot that bears a pair of ephemeral bracts. Each staminate inflorescence similarly produces a terminal flower and, usually, a third-order, racemose axis in the axil of each pair of bracts. Each flower on these indeterminate axes is in the axil of a bract. On the abaxial side immediately below the perianth, each flower has a bracteole, which is produced by the floral apex. Three tepal primordia are initiated on the margins of the floral apex in an acyclic pattern. Subsequent intercalary growth produces a perianth tube. Alternate with the tepals, three anther primordia arise on the margins of a broadened floral apex in an acyclic or helical pattern. Usually two more anther primordia arise adjacent to each of the first three primordia, producing a total of nine primordia. At this stage the floral apex begins to lose its meristematic appearance, but the residuum persists. Intercalary growth below the floral apex produces a columnar receptacle. The anther primordia remain adnate to the receptacle and grow longitudinally as the receptacle elongates. Each primordium develops into an anther with two pairs of septate, elongate microsporangia. In pistillate flowers, a carpel primordium encircles the floral apex eventually producing an ascidiate carpel with a cleft on the oblique apex and upper adaxial wall. The floral ontogeny supports the morphological interpretation of myristicaceous flowers as trimerous with either four-sporangiate anthers or monocarpellate pistils.