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In biennial plants, the age of flowering is constrained, but size at flowering is highly variable. This suggests that performance at the flowering stage depends largely on growth conditions at the rosette stage. We examined this possibility using Erysimum strictum P. Gaertn., B. Mey., and Scherb. (Brassicaceae), a strictly biennial herb, the reproductive output of which increases with increasing plant height and branch number. In a common garden experiment, we defoliated (50% of leaves removed twice) and fertilized (three times) individual plants at the rosette stage and studied their performance at the flowering stage in the following year. Rosette defoliation adversely affected all performance measures except seed number per fruit and seed weight. Fertilization did not alleviate these effects. Defoliation reduced seed set by 48% in fertilized plants and 29% in unfertilized plants. Fertilization stimulated branch production from the rosette base but did not significantly affect plant height. These observations suggest that, in the case of basally unbranched plants, apical dominance by the leading stalk suppresses the axillary meristems at the rosette base. Fertilization at the rosette stage can break this suppression. The induction for breakage presumably occurs before bolting since, in our earlier experiments, neither fertilization nor apical damage at the flowering stage stimulated branching from the base. Erysimum strictum is likely to be selected for fast vertical growth at the start of bolting, and hence plant height is a less plastic trait with respect to resource availability than branch number. Regression analysis suggested that, in response to rosette fertilization, small plants invest in height growth instead of branching, whereas large plants to a greater extent invest their supplemental resources in vigorous branching. Consequently, resource availability at the rosette stage influences apical dominance at the flowering stage. Unexpectedly, however, improved resource availability did not alleviate the cost of simulated rosette-stage herbivory.Key words: apical dominance, biennial, fitness, herbivory, resource availability, rosette stage.

We have identified three phases within the wild-type Arabidopsis thaliana (L.) Heynh. rosette, based on significant differences in leaf shape, size, vascular pattern, and presence of abaxial trichomes. To test the hypothesis that a single, central mechanism controls the progression through all plant phases and that conditions that alter the time to flowering will also alter the progression through vegetative phases, we analysed the rosette phases under such conditions. In support of our hypothesis, we determined that those conditions (loss of LEAFY activity, short days) that decelerate time to flowering show decelerated progression through the rosette phases, while those conditions (loss of TERMINAL FLOWER, overexpression of LEAFY, low light) that accelerate time to flowering show accelerated progression through the rosette phases. In all conditions except short days, the length of the first phase was unaffected, indicating that this phase is less susceptible to influences of the central mechanism. Progression through the subsequent two rosette phases was accelerated differentially, such that the second phase was affected more strongly than the first. This supports the idea that, in the rosette, as in the inflorescence, the inhibition of phase transition by the central mechanism is gradually decreasing.Key words: phase change, flowering time, Arabidopsis thaliana, LEAFY, TERMINAL FLOWER, heteroblasty.

Improved culture methods and the application of cryotechniques in light and electron microscopy have allowed new insights at the organismic and cellular levels in mycobiont–photobiont relations of selected lichen species. Growth, regenerative capacity, and the ability to cope with spatial disturbances were tested in the foliose macrolichens Xanthoria parietina and Parmelia sulcata. These mycobionts can sense and partly correct an inverted position and thus insure adequate illumination for the photobiont cell population. In both taxa, the apical/marginal pseudomeristem and adjacent elongation zone bend backwards. Parmelia sulcata continues this bending process and grows arch-like until its margin reaches the substratum. Xanthoria parietina stops bending and growing but regenerates new primordial stages along the marginal rim and cut edges. These primordia develop into new lobes with a normal upside up topography. Its remarkable regenerative capacity permits X. parietina to develop a new rosette from an assembly of minute thallus fragments that had been fixed to a ceramic substratum. Cryotechniques applied at the light and electron microscopy levels allow us to visualize drought stress induced structural alterations at the cellular level in lichen bionts. Neither partner of the symbiosis plasmolyses under extreme drought stress. The globose to ovoid green algal or cyanobacterial photobiont cells and their walls shrivel dramatically but the fungal cell wall cannot be deformed to such a high degree during stress events. Ascomycetous lichen mycobionts of three different orders formed a large, intracellular gas bubble of unknown ontogeny and content when their turgor pressure dropped to very low values. This cytoplasmic "air bag" allows the protoplast to shrink and, at the same time, to keep the cell membrane in contact with the wall. In the desiccated state many lichens tolerate extreme stress conditions. Thallus fragments of dry X. parietina grew normally after having been cryofixed in subcooled liquid nitrogen, sputter coated, and examined in a low temperature scanning electron microscope. Fully hydrated samples did not survive this treatment. Key words: culturing experiments, regenerative capacity, drought stress, LTSEM, freeze substitution, intracellular gas bubble.

Within the tribe Veroniceae (Scrophulariaceae), Synthyris and Besseya have been grouped at times with Wulfenia, because of their rosette habit, and with cauline-leaved Veronica, because of similarities of pollen and seed morphology. Floral development patterns of Synthyris reniformis, Besseya alpina, and Wulfenia carinthiaca were studied with quantitative methods to contribute additional evidence towards resolving the phylogenetic relationships of those genera. For each species, 19 flower organ measurements were taken on each of 50 buds from all stages of development. Compared to the fast early corolla development observed in most Scrophulariaceae, all species examined shared a delay in early corolla tube growth which was less extreme than that observed in Veronica. A strong delay in early corolla lobe growth was shared only between Veronica, Synthyris, and Besseya. This derived attribute is a possible synapomorphy supporting hypotheses of monophyly of those genera. Summarizing all measurements with multigroup principal components analysis showed that the overall floral allometries of Wulfenia have more similarity with those of Digitalis than with Veronica and relatives; this concurs with evidence from vegetative and reproductive morphology. Key words: floral development, allometry, phylogeny.

In a random block field experiment, life-history traits associated with colonizing ability of diploid and tetraploid cytotypes of Capsella (Brassicaceae) were compared. These were germination, flowering, growth-form parameters, and leaf shape. Data are not in favour of differences in germination behaviour between the diploid and tetraploid Capsella species, as germination rate and capacity are highly influenced by inception and release of seed dormancy. Although our data at first glance seem to suggest that diploid C. rubella start flowering later than tetraploid C. bursa-pastoris, considerable ecotypic variation for flowering in both species makes it difficult to assign an effect specifically to ploidy level. We also conclude that plant height, rosette diameter, and branching number are not directly determined by ploidy level. In contrast however, leaf shape is clearly determined by ploidy level. In the light of all available data including data of previous experiments, we suggest that gene duplication by polyploidization may have been a key element that provided C. bursa-pastoris with additional genetic flexibility. It is not primarily the gain of colonization ability, as both species are weeds and colonizers. Rather, the greater genetic flexibility enabled C. bursa-pastoris to extend its range beyond that of C. rubella. Key words: ploidy level, germination, flowering, growth form, leaf morphology, Capsella.

The leaves of the carnivorous bromeliad, Brocchinia reducta, are clustered in a tight vertical rosette, forming a water-collecting tank in which insects are trapped. Evidence in the literature indicates that nutrient uptake into the leaves occurs primarily, if not entirely, via trichomes located at the base of the leaves on the tank side. The outer cell wall in the trichomes from the carnivorous bromeliad B. reducta has an unusual ultrastructure. This wall has a labyrinthine-like appearance of light and dark-staining regions that suggests a highly specialized function. This study examined three structural aspects of this wall. First, the limiting porosity of the trichome wall was examined with fluorescently labelled dextrans and shown to permit the transport of molecules as large as 6.6 nm. Second, structural changes in a dehydrated wall were observed using freeze-substitution techniques. Specifically, the electron transparent wall "regions" were collapsed when the trichome was dried. Last, the presence of periodic acid soluble polysaccharides was detected throughout the electron-dense wall protuberances, but occurred only as thin, dispersed strands in the more electron-transparent regions. We have concluded from these studies that in the hydrated state, these electron-transparent regions represent the channels through which solutes move through the wall to the cap cell surface. A pore size of 6.6 nm would also permit the movement of modest-size proteins, and based on previous observations, we suggest that protein uptake into the cells would occur by pinocytosis. We found channels can vary in size and thus porosity; in the dehydrated state, the wall is considerably shrunken and the channels collapse. We hypothesize that the shrunken wall restricts the loss of water from leaves through trichomes to the atmosphere. Key words: Bromeliaceae, cell wall porosity, fluorescently labelled dextrans, freeze-substitution, Thiéry staining.

The technique of demography of parts was used to study the phenotypic plasticity of Chrysanthemum leucanthemum (ox-eye daisy). Plants were cloned and submitted to two separate experiments: three treatments of light intensity and three treatments of nutrient levels. Plant parts (leaves, branches, capitula, stems) were marked at regular intervals during the growing season. Leaves present at the time of transplant generally died earlier when light and nutrient treatments were reduced. However, the number and survivorship of the main stem leaves did not show any significant difference among treatments. In general the number of first-order branches, stems, capitula, and rosette leaves decreased with low light intensity and low nutrient levels. Demography of parts is a dynamic approach, allowing the study of cumulative production of leaves, branches, and capitula. Other techniques, such as traditional growth analysis and study of resource allocation, are more static and descriptive.

The developmental ontogeny of eugymnohymenial apothecia in Ascodesmis nigricans van Tieghem and A. sphaerospora Obrist, homothallic operculate Discomycetes (Pezizales, Pyronemataceae), was investigated from initiation of the T-shaped gametangial initials through spore discharge. Branching of these T-shaped side branches gave rise to gametangia that paired and coiled helically. Paraphyses proliferated from the base of the rosette of gametangia and enveloped the coils, which appeared to undergo plasmogamy at their apices. Although a loose peridium of paraphyses was formed, a true excipulum was absent. Displacement of the opercula on the positively phototropic asci was towards the more strongly illuminated side.

A previously unreported method of asexual reproduction has been found in Barbarea vulgaris. It involves the formation of a rosette of leaves (similar to those of the basal rosette) on the inflorescence after seed formation. If the stalk is bent to the ground, adventitious roots from the cauline rosette can become established. Eventually, if it survives overwinter, this new plant may bolt and flower.

Rumex crispus (curled dock) overwinters as a rosette. Growth of the rosette begins in the middle of April and the panicles emerge after about 4 to 6 weeks. Anthesis starts in the middle of a panicle and proceeds basipetally and acropetally on the main rachis and outward on the primary and secondary branches. The seeds mature from the end of July to the middle of August.The perianth is a major portion of the total chlorophyll-containing tissue of the panicle. Perianth segments enclosing the seeds contribute significantly to the dry matter of seeds. The contribution is highest when the perianth is young. The growth in length and width of seeds is complete 8 days after anthesis.

The periplast of Cryptomonas sp. θ covers most of the cell surface and is composed of the plasma membrane sandwiched between inner and surface periplast components. The surface periplast component is tightly appressed to the plasma membrane and consists of irregularly shaped plates composed of subunits organized into a crystalline array. Noncrystalline material distinguishes plate borders, and changes in plate size and (or) shape may result from the addition or subtraction of subunits at the borders. The inner periplast component is difficult to discern, but normally appears as a thin sheet of material appressed to the cytoplasmic surface of the plasma membrane. The inner periplast component is not closely associated with the plasma membrane at the positions corresponding to plate borders in the overlying surface periplast component. Both periplast components end at the entrance to the vestibulum, which together with the gullet is covered by a surface layer of heptagonal "rosette scales." The size and shape of the surface periplast plates, as well as the degree of association of the inner periplast sheet with the plasma membrane, are mirrored in the P and, to a lesser degree, E fracture faces of the plasma membrane. The presence of distinct membrane domains suggests the plasma membrane may be directly involved in the assembly and subsequent development of the periplast layers.

Young plants of the cold-hardy winter wheat (Triticum aestivum L. emend. Thell.) Kharkov 22 MC did not develop atypical prostrate or rosette growth habit unless light supply exceeded 350 klux∙h∙day−1. Prostrate habit developed under both short (10-h) and long (16-h or 24-h) photoperiods. Under a given photoperiod, expression of this trait intensified as light intensities increased. This finding was demonstrated in both field and growth-cabinet experiments. The degree of development of the rosette growth habit may be assessed by plotting plant height against plant age. Plants that develop typical rosettes decline in height when the rosettes develop whereas plants that remain erect show a continuous increase in height.

Virus isolates obtained from peach with rosette mosaic and from grapes with ‘decline’ in Michigan have a similar host range and in vitro properties and morphology and are related serologically. Particles are isometrics averaging 28 nm in diameter. Isolates of virus from both sources, where transmitted manually, induced rosette mosaic on peach and decline on grapes.The virus is seed-borne in Chenopodium quinoa Willd., but it is not transmitted by Cuscuta campestris L. or by Myzus persicae Sulz. Partially purified virus preparations contain two infectious and serologically active components with sedimentation coefficients (s20,w) of 115 and 134, with molecular weight of 5.5 and 6.3 daltons, and with estimated values of 37 and 44% ribonucleic acid (RNA), respectively. The UV absorption at 254 nm of the middle and bottom infectious components is not dependent on the time after inoculation of C. quinoa, suggesting that the slowest component is not a precursor of the virus. Both components were reproduced when each was inoculated separately into C. quinoa. Virus isolates recovered from infected grapes varied in virulence, and serological differences could be detected by cross absorption and immunodiffusion tests. The name peach rosette mosaic virus (PRMV) is proposed for the virus responsible for the grape decline. The cryptogram of the virus is(R)/*;*/*;S/S;S/Ne.

A dwarf plant isolated from anther culture of a normal genotype of birdsfoot trefoil (Lotus corniculatus L. cv. Leo) has been isolated, characterized, and maintained as an in vitro shoot-tip culture. The dwarf condition is the result of a much shorter internode length when compared with a normal genotype in shoot tip culture. Dwarf shoots which are typically rosette respond to increased GA3 levels by increased internode growth. Normal genotypes are inhibited and eventually die as a result of increased levels of GA3 in the culture medium. This dwarf has the normal tetraploid chromosome number of 24, and although stable in shoot tip cultures since 1977, has not survived outside of in vitro shoot tip cultures.

Purified preparations of peach rosette mosaic virus (PRMV), were shown by rate-zonal centrifugation in sucrose and equilibrium centrifugation in CsCl to be composed of two nucleoprotein components with buoyant densities of 1.47 (middle) and 1.51 (bottom) g/cm3. The virus contains two RNA species with molecular weights of 2.5 × 106 (RNA 1) and 2.2 × I06 (RNA 2), and a single protein subunit with a molecular weight of 57 000. RNA 1 and RNA 2 reside separately in components B and M, respectively. Both RNAs are required for infection thus indicating that the virus has a divided genome. The nucleotide composition of both RNAs is similar except for cytidilic acid. The hyperchromic profile for the M component is broader than that of B and the Tm value is higher (for M Tm = 55 °C; for B Tm = 48 °C). Particle disruption and release of RNA progresses slowly over the absorbance–temperature transition. Only half of the particles were dissociated at the Tm value. Freezing dissociates most of M component into RNA 2 and protein but had no effect on the B component. Sodium chloride protected the M particles from low temperature disruption. The data support the conclusion that PRMV is a nepovirus with particular properties of the tomato ring-spot virus (TomRSV) subgroup.

Wild celery (Vallisneria americana, Hydrocharitaceae) is a common submersed freshwater macrophyte rarely reported from lakes with pH below 6. Plants grown in a greenhouse on a uniform sediment within pH-controlled tanks all survived 60 days at pH 5 but showed reduced dry matter accumulation (by 76%), leaf area (by 79%), and rosette and winter bud production (by 44 and 63%, respectively) compared with plants grown at pH 7.5. The sensitivity of this plant to only moderate acidity did not differ for plants in water acidified to pH 5 by a combination of H2SO4 and HNO3 or by HCl, indicating that the former acids exerted no fertilizing effects to counter the detrimental influence of acidification. Tissue nitrogen and phosphorus levels were well above the critical concentrations previously reported for this species. Tissue calcium and manganese concentrations showed no clear relationship to treatment pH. Both aluminum and iron levels in tissues were twofold to threefold higher for the smaller plants grown at pH 5 (means of 1970 and 3090 μg/g, respectively), suggesting that metal toxicity may have caused growth reduction at low pH.

Hieracium floribundum is a rosette species requiring a number of long days for flower induction. Histological studies of vegetative, transition, and floral apices showed the structural changes associated with flower induction in this species. One striking histochemical change observed was the absence of starch in vegetative apices and the accumulation and retention of quantities of starch in prefloral and floral apices. A study of initiation and development of axillary buds at the time of flowering revealed that there was a gradient in the potential to flower shown by these buds along the developing flower stalk to the base of the plant. The buds in the axils of upper peduncle bracts always develop as capitula while the apices of the buds in the axils of the next few bracts assume the shape of floral buds but fail to develop unless the upper developing inflorescences are removed. Buds in the axils of the lowest bracts and upper (youngest) leaves have the potential to form rosettes, stolons, or inflorescences depending on the environmental conditions in which the plants are grown. Buds formed in the lower (oldest) leaf axils normally fail to grow out until after seed set when a few may develop as rosettes. Possible explanations for these results are discussed, and some experimental approaches being used to elucidate the physiological basis for bud expression are indicated.

The plumule in rosette plants showing the phenomenon of "pseudomonocotyly" remains in a quiescent stage at the base of the cotyledonary tube, and this quiescent stage appears to be due to the inhibitory influence of the cotyledons. This correlative inhibition in which the development of the embryonic apical region is influenced by the cotyledon may be an important survival adaptation in alpine rosettes.