摘要:

Marcgravia rectifoliaL. is a dimorphic vine having distinct juvenile and adult shoots. The juvenile shoot is a climber characterized by an orthotropic growth habit, a flattened stem, adventitious roots, and ovate leaves. The adult shoot, on the other hand, possesses a plagiotropic growth habit, has a cylindrical stem, few or no adventitious roots, and lanceolate leaves. Both phases have distichous phyllotaxy, however the plastochron is shorter for the adult phase than for the juvenile. Internode elongation occurs earlier for adult shoots than for juvenile shoots. Cytological analyses show the flattened stem of the juvenile results from differential production of cells, especially in the pith region. On the other hand, internodes of the adult phase are longer than juvenile internodes, a result of more cells produced rather than longer cells. In juvenile stems a perivascular band of elongated fibers develops, while in adult stems this band consists of brachyosclereids. Both phases undergo secondary growth and have non‐storied cambia. Cambial activity begins in the 6th internode of each phase. As secondary growth proceeds, the adult stem produces much more xylem than juvenile stems of the same age. Adventitious roots produced in the juvenile stem are located in vertical rows at the “corners” of flattened stems and are attachment structures aiding the climbing habit of this vine. Phase changes occur regularly in this species. The juvenile phase usually transforms into the adult, however the adult phase can spontaneously revert back into the juvenile phase. The anatomical features and the phase changes are discussed and compared toHedera helix,a vine whose phase changes have been studied in some detail. It is suggested that the anatomical features ofMarcgravia rectifoliaL. including its phase changes, may provide an alternative system to study physiological changes similar to those done withHedera helix.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07915.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The dormant (mid‐November to mid‐February) microsporangia ofPseudotsuga menziesii(Douglas‐fir) contain pollen mother cells (PMC's) in diffuse diplotene, surrounded by 1–2 layers of tapetal cells and 3–4 layers of microsporangial wall cells. At the beginning of dormancy, PMC's are large and their walls are lysed. The cell walls contain a thick layer of loosely‐arranged fibrils which are produced in large vesicles in the PMC cytoplasm and are secreted across the plasma membrane. PMC's contain several layers of rough ER. The inner tangential and the radial walls of the tapetal cells are lysed. During dormancy the PMC's form many new autophagic vacuoles, the chromatin consists of a network of fine threads comprised of medium‐sized granules of uniform size and the nucleoli split. The outer tapetal wall is thick and becomes encrusted by an irregular lipid layer. The tapetal cytoplasm is similar to the PMC cytoplasm but is devoid of amyloplasts. The tapetal cytoplasm shows secretory activity at the beginning of dormancy and again near the end of dormancy. The later secretory activity results in the deposition of a spongy material, especially along the radial and inner walls of the tapetal cells. Tapetal cells contain 1–2 large nuclei which show prominent and irregular clumps of chromatin. Subcellular developmental changes occur in the dormant microsporangia ofPseudotsugain much the same manner as has been reported forPinus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07916.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

A program of experimental field pollinations was carried out on 14 species of woody Rubiaceae in a Costa Rican wet forest in order to test for the presence of self‐incompatibility systems. Species ofCephaelis, Coussarea, Faramea, Hamelia, Posoqueria, Psychotria, Rudgea,andWarszewicziawere investigated in the study. Ten of the species are distylous, and of these, nine were found to be self‐incompatible. The site of the incompatibility barrier varied between and within species. Short style plants always had stigmatic inhibition of pollen tubes following self and intraform pollinations, but the site of the rejection response in long style plants was quite variable. In several species, pollen tubes, resulting from incompatible pollinations of the long style flowers, penetrated to the base of the style. Fruit set was followed in two of these species, and despite deep penetration of self and intraform pollen tubes in the long style morph, only interform pollinations resulted in fruit set. Four of the species tested are florally monomorphic and each was found to be self‐incompatible on the basis of fruit set patterns. Pollen tubes in the styles of self‐pollinated flowers of two of the monomorphic species, penetrated to the ovary, but no fruits resulted from selfpollinations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07917.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Structure and distribution of vascular bundles (VB) have been investigated in petioles of 26 herbaceous and woody dicotyledons. No single pattern of vascular bundle distribution could be found for both groups of plants. Both groups of plants had VB patterns ranging from a cylinder to separate bundles arranged in a variety of patterns, e.g., distorted cylinder, various configurations of a crescent, and other types. The total number of xylem vessels in herbaceous and woody plant petioles varied between 110 and 1756.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07918.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Nickel and zinc were determined in 57 taxa of western North American genera containing serpentine‐tolerant species. The studies resulted in the identification of three varieties ofThlaspi montanum(var.montanum,var.siskiyouense,and var.californicum) which are hyperaccumulators (>1,000 μg/g dry mass) of nickel. These three taxa together with the previously reportedStreptanthus polygaloidesare the only hyperaccumulators of nickel so far reported for continental America. Significantly higher than normal nickel values (up to 664 μg/g) were recorded for the serpentinophyteViola cuneata. Elevated zinc levels (>1,000 μg/g dry mass) were also recorded in four of theThlaspitaxa and confirm the tendency of many species of this genus to accumulate zinc. It is suggested that hyperaccumulation of nickel by the three varieties ofT. montanumis a neo‐endemic rather than palaeo‐endemic process and that the precursor of these varieties isT. montanumvar.montanumfrom non‐mineralized soils.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07919.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The development of secondarily derived features in orchid pollen precludes the possibility of applying evolutionary trends hypothesized for dicot pollen to orchid pollen and perhaps even monocot pollen. There are three lines of pollen wall development, all secondarily derived from a possible tectate‐perforate ancestral type, i.e., tectate‐imperforate with incipient columellae (Cypripedioideae), intectate lacking a foot layer (Orchidoideae), and tectate‐imperforate with globular masses of sporopollenin (Vandoid Epidendroideae).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07920.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

The flowers ofAmyema miqueliiandA. miraculosumare protandrous and pollinated by birds. Their dry‐type stigmatic surface is composed of unicellular papillae. At the male phase, these papillae are constricted with rugulose surfaces. During the transition to the female (pollen receptive) phase these cells expand, almost doubling in width while their surface becomes much smoother. Beneath the thin proteinaceous pellicle, the papillar wall consists of an extraordinarily thick bi‐layered cuticle overlying the primary wall. The two layers of the cuticle are stained by lipid dyes, but are distinguished by their different responses to other cytochemical tests. The reaction product for the enzyme esterase is present within crenulations on the papillar surface in small amounts, and in dense deposits in the cuticular clefts at the base between papillae. Not surprisingly, pollen tubes are unable to penetrate the thick papillar cap and enter the style through these clefts. The unusual thickness of the cuticle is interpreted as an adaptive response to pollination by perching birds (passerines) probing for nectar.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07921.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Morphology and meiosis are described in four progeny plants resulting from tetraploidGrindelia camporumGreene (2n= 24) from California pollinated by diploidG. grandifloraHook. (2n= 12) from Coahuila, Mexico. Three of the four progeny were tetraploid, morphologically like the pistillate parent, and had metaphase I chromosome configurations which included quadrivalents and a complementary number of bivalents. They are considered to have resulted from selfing. The fourth plant was triploid (2n= 18) andmorphologically intermediate between the parents. Chromosome configurations in the triploid were variable with univalents, ring and rod bivalents, trivalents and pentavalents. These two species are considered related through an ancestor with a basic genome, but are separated cytologically by polyploidy and by two distinct chromosomal interchanges that explain the configurations observed in the triploid hybrid.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07922.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Somatic nuclear divisions in sporangiogenous plasmodia ofWoronina pythiiGoldie‐Smith were studied with transmission electron microscopy. During metaphase, each nucleus formed a cruciform configuration as chromatin became aligned at the equatorial plate perpendicular to the persistent nucleolus. Except for polar fenestrations, the original nuclear envelope remained intact throughout the mitotic division. Intranuclear membranous vesicles appeared to bleb off the inner membrane of the original nuclear envelope, adhered to the surfaces of the separating chromatin, and eventually formed new daughter nuclear envelope within the original nuclear envelope. During the first 24 hr of vegetative plasmodial growth, each telophase nucleus exhibited an obvious constriction of the original nuclear envelope in the interzonal region. Similar constrictions were not evident in telophase nuclei found in 24–36‐hr‐old plasmodia. This variation in the ultrastructural morphology of cruciform division appears to be related to the age and size of each sporangiogenous plasmodium, and is the first to be documented within this group of fungal pathogens.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07923.x

出版商:Wiley    

年代:1983

数据来源: WILEY

摘要:

Transmission electron microscopy of pre‐release and post‐release biflagellate gametes ofCephaleuros virescenshas produced comparative data on these cells and on the detailed absolute arrangement of the flagellar apparatus. In all major respects including the presence of two multilayered structures (MLS's) the closely compacted, non‐motile but mature pre‐release gametes are similar to the mature, free swimming post‐release gametes. The elongated shape of the free‐swimming gametes differs from the more compact form of the pre‐release gametes, but does not reflect a major difference in the arrangement of internal components. The flagella are bilaterally keeled and each keel contains a cylindrical element. Each flagellar base is encircled by a densely staining collar of modified plasmalemma at the point of entry into the apical papilla. The equal anterior flagella enter the papilla from opposite sides; their basal bodies are parallel and overlapping. Each terminates in a densely staining terminal cap. No capping plate is present. Each basal body is associated both with a three‐layered MLS, the anterior layer of which becomes a lateral microtubular spline of 2 to 8 microtubules, and with an additional medial compound root of two layers of microtubules (2 over 4 or 5). Both the compound microtubule root and the spline may acquire additional microtubules as they extend distally in close proximity to mitochondria and the plasmalemma. No striated roots, or rhizoplasts, have been observed. Two densely staining plaques are associated with the plasma membrane at specific anterior sites and may be comparable to the presumptive mating structures seen in other green algal motile cells. The reversed bilateral symmetry of the cells produces two possible arrangements of the flagellar apparatus, namely, a 11/5 (or left‐handed) arrangement or a 1/7 (or right‐handed) arrangement. Only 11/5 cells have been found. Despite the presence of distinct multilayered structures, some aspects of the gametes ofCephaleurosquite closely resemble the cruciate motile cells of algae now regarded by some authors as typical of Ulvophyceae, sensu Stewart and Mattox.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1983.tb07924.x

出版商:Wiley    

年代:1983

数据来源: WILEY