Mode Of Vegetative Reproduction Research Articles

Redistribution of water via layering branches between connected parent and daughter trees in Norway spruce clonal groups

Key message We measured sap flow and shoot water potentials in clonally connected parent and daughter trees. We found bidirectional flow patterns in branches mediating the connection between parent and daughter trees. Abstract Layering is an important mode of vegetative reproduction at treeline, in which clonal daughter trees are formed by the rooting of lower (''layering'') branches of the parent tree. These branches mediate the connection between parent (PT) and daughter tree (DT). Here, we measured quantity and direction of sap flow in layering branches as well as PT and DT, and measured shoot water potentials in the crowns of a connected PT and DT. We found bidirectional sap flow pattern in layering branches, with the bidirectionality of the flow resulting from water potential dynamics of the parent and daughter trees varying diurnally. We found that 4.3 % of the total water transpired by the DT was supplied by the PT root system, with up to 25 % of the instantaneous daughter tree sap flow coming from the parent tree. In contrast, water provided by the daughter's root system to the parent tree comprised only a negligible amount, less than 1 % of the parent's entire sap flow. Additionally, after experimental excavation of part of the DT roots, layering branch flow towards the DT in- creased, while flows in the opposite direction almost van- ished. This study showed that aboveground clonal connections can facilitate a new type of hydraulic redis- tribution where water is transported bidirectionally through branches. This transfer of water and nutrients is vital especially in the first years of the daughter tree but supplies considerable amounts of water even several years after the establishment of a new clonal tree.

Systematics of the hypervariable <i>Moraea tripetala</i> complex (Iridaceae: Iridoideae) of the southern African winter rainfall zone

Field and laboratory research has shown that the Moraea tripetala complex of western South Africa, traditionally treated as a single species, sometimes with two additional varieties, has a pattern of morphological and cytological variation too complex to be accommodated in a single species. Variation in floral structure, especially the shape of the inner tepals, degree of union of the filaments, anther length and pollen colour form coherent patterns closely correlated with morphology of the corm tunics, mode of vegetative reproduction, and in some instances capsule and seed shape and size. The morphological patterns also correlate with geography, flowering time and sometimes habitat. It is especially significant that different variants of the complex may co-occur, each with overlapping or separate flowering times, a situation that conflicts with a single species taxonomy. We propose recognizing nine species and three additional subspecies for plants currently assigned to M. tripetala. M. grandis, from the western Karoo, has virtually free filaments and leaves often ± plane distally; closely allied M. amabilis, also with ± free filaments and often hairy leaves, is centred in the western Karoo and Olifants River Valley. Its range overlaps that of M. cuspidata, which has narrowly channelled, smooth leaves, linear inner tepals spreading distally and filaments united for up to 1.5 mm. M. decipiens from the Piketberg, M. hainebachiana, a local endemic of coastal limestone fynbos in the Saldanha District, M. ogamana from seasonally wet lowlands, and early flowering M. mutila constitute the remaining species of the complex in the southwestern Western Cape. M. helmei, a local endemic of middle elevations in the Kamiesberg, Namaqualand, has small flowers with short, tricuspidate inner tepals. All but M. amabilis and M. mutila are new species. We divide M. tripetala sensu stricto into three subspecies: widespread subsp. tripetala, subsp. violacea from the interior Cape flora region, and late-flowering subsp. jacquiniana from the Cape Peninsula and surrounding mountains.

New insights into placozoan sexual reproduction and development.

Unraveling animal life cycles and embryonic development is basic to understanding animal biology and often sheds light on phylogenetic relationships. A key group for understanding the evolution of the Metazoa is the early branching phylum Placozoa, which has attracted rapidly increasing attention. Despite over a hundred years of placozoan research the life cycle of this enigmatic phylum remains unknown. Placozoa are a unique model system for which the nuclear genome was published before the basic biology (i.e. life cycle and development) has been unraveled. Four organismal studies have reported the development of oocytes and one genetic study has nourished the hypothesis of sexual reproduction in natural populations at least in the past. Here we report new observations on sexual reproduction and embryonic development in the Placozoa and support the hypothesis of current sexual reproduction. The regular observation of oocytes and expressed sperm markers provide support that placozoans reproduce sexually in the field. Using whole genome and EST sequences and additional cDNA cloning we identified five conserved sperm markers, characteristic for different stages in spermatogenesis. We also report details on the embryonic development up to a 128-cell stage and new ultrastructural features occurring during early development. These results suggest that sperm and oocyte generation and maturation occur in different placozoans and that clonal lineages reproduce bisexually in addition to the standard mode of vegetative reproduction. The sum of observations is best congruent with the hypothesis of a simple life cycle with an alternation of reproductive modes between bisexual and vegetative reproduction.

Mode of vegetative reproduction of the bipolar budding yeast species Wickerhamomyces pijperi and related strains

To clarify the budding pattern of Wickerhamomyces pijperi, the vegetative cells were observed by scanning electron microscopy. The cells grew by bipolar budding, but cells that budded from the shoulder of a mother cell were occasionally observed. We examined the cell morphology and phylogeny of five strains of Wickerhamomyces sp. isolated in Thailand as well as seven W. pijperi and three Wickerhamomyces sp. strains that were preserved in culture collections. Phylogenetic analysis based on three different nucleotide sequences (D1/D2 domain of 26S rDNA, the actin gene ACT1 and the elongation factor 2 gene EF2) indicated that all the strains belonged to the genus Wickerhamomyces and were neighbours of the type strain W. pijperi NBRC 1290(T). The strains fell into two groups in this analysis. The budding patterns of the strains were carefully observed by staining the bud scars, and these patterns were categorized into three groups: types I-III. Type I included cells that grew by bipolar budding and formed multiple scars, type III included cells that grew by multilateral budding and formed a single scar, and type II included cells that exhibited a mixture of type I and type III patterns. Among the 15 strains, 12 strains, including W. pijperi NBRC 1290(T), mainly exhibited type I or type II budding patterns; these strains belonged to group 1 of the phylogenetic analysis. The remaining three strains, which belonged to group 2, exhibited either type II or type III patterns. Thus the phylogenetic relationship and budding patterns are related. Moreover, some cells also exhibited budding characteristics that were intermediate between bipolar and multilateral budding.

Sympagohydra tuuli (Cnidaria, Hydrozoa): first report from sea ice of the central Arctic Ocean and insights into histology, reproduction and locomotion

Various cnidarians have adapted their life style to interstitial habitats of marine sediments. Recently, for the first time a hydroid was reported from the interstitial brine channel system of Arctic fast ice. Due to its derived features, the new genus and species Sympagohydra tuuli was introduced. Here we describe findings of S. tuuli in sea ice at several sites within the central Arctic Ocean. In our view the results of this study do not allow assignment of Sympagohydra to any known family and we, therefore, suggest the introduction of a new family Sympagohydridae which is placed within the hydrozoan subclass Hydroidolina, order Anthomedusae, suborder Capitata. A first detailed histological analysis of S. tuuli is presented. In vivo analysis of locomotion and reproduction revealed a remarkable convergent evolution in S. tuuli and distant meiobenthic relatives. Shared traits are a flagellated epidermis enabling the animals to glide within small interstices by means of flagellar beating as well as an internalised embryogenesis. In S. tuuli gametogenesis occurs in the absence of gonophores inbetween gastro- and epidermis clearly separated from the epidermis. Budding was observed as the vegetative mode of reproduction. Documentation of feeding behaviour identified copepod nauplii and rotifers as prey items and demonstrates a high trophical position of the hydroids within the sympagic food web. Occurrence of reproducing individuals and pronounced tolerances towards changing temperatures and salinities indicate S. tuuli as a truly sympagic species.

Hybrid origin of the arctic � Pucciphippsia vacillans (Poaceae): evidence from Svalbard plants

The hypothesised hybrid origin of the High Arctic grass × Pucciphippsia vacillans from the putative parents Puccinelliavahliana, Phippsia algida or Phippsia concinna was investigated by analyses of morphological, cytological, and enzymatic data. Chromosome counts showed that × P. vacillans from Svalbard is triploid (2n = 21) and sterile, supporting the hypothesis of a hybrid origin. Enzymatic investigations showed that × P. vacillans is identical to Phippsia in most enzyme markers and furthermore that all four taxa are closely related. Additive banding pattern in one enzyme system (6-PGD) as well as some morphological traits indicated that × P. vacillans is a Puccinellia × Phippsia hybrid. × Pucciphippsia vacillans is morphologically intermediate between Phippsia algida and Puccinellia vahliana in several individual characters as well as in a multivariate analysis, indicating that Phippsia algida is the more probable Phippsia parent. Mature seeds have never been observed in × P. vacillans and the taxon has no known mode of vegetative reproduction. This investigation suggests that it might be a sterile first-generation hybrid wherever it occurs in Svalbard. The close genetic relationship between × Pucciphippsia, Phippsia, and Puccinellia vahliana has implications for their generic delimitation and might suggest that only one genus is involved.

Genetic and morphological analysis of two novel nutsedge biotypes from California

The identities of two novel perennial nutsedge biotypes collected near Bakersfield, CA, were assessed using isozyme and random-amplified polymorphic deoxyribonucleic acid markers in conjunction with morphological analysis. The two biotypes, designated as CK (Cyperus rotundus cv. ‘Kempeni’) and CR (Cyperus esculentus cv. ‘Robusta’), morphologically resemble purple nutsedge and yellow nutsedge, respectively. Plants from both biotypes exhibited more prolific growth than the typical forms and possessed some traits that are not characteristic of the species they resemble. The morphological study was conducted on a total of 15 purple nutsedge, yellow nutsedge, CK, and CR populations collected in the first year and on 20 additional nutsedge populations were collected in the second year. The genetic analysis was performed on populations from the first year only. In general, there was agreement among the results obtained from the morphometric, isozymatic, and deoxyribonucleic acid studies. Populations of CR clustered with yellow nutsedge populations, indicating that CR is within the normal range of variation of this species and may represent a new introduction. Populations of CK, however, were distinct from both purple nutsedge and yellow nutsedge populations. Considering the low level of genetic variation reported in purple nutsedge and its strict vegetative mode of reproduction, CK might represent a sexually reproducing ecotype of purple nutsedge or a hybrid with yellow nutsedge.

Genetic structure and differentiation in cultivated grape, Vitis vinifera L.

222 cultivated (Vitis vinifera) and 22 wild (V. vinifera ssp. sylvestris) grape accessions were analysed for genetic diversity and differentiation at eight microsatellite loci. A total of 94 alleles were detected, with extensive polymorphism among the accessions. Multivariate relationships among accessions revealed 16 genetic groups structured into three clusters, supporting the classical eco-geographic grouping of grape cultivars: occidentalis, pontica and orientalis. French cultivars appeared to be distinct and showed close affinity to the wild progenitor, ssp. sylvestris from south-western France (Pyrenees) and Tunisia, probably reflecting the origin and domestication history of many of the old wine cultivars from France. There was appreciable level of differentiation between table and wine grape cultivars, and the Muscat types were somewhat distinct within the wine grapes. Contingency chi2 analysis indicated significant heterogeneity in allele frequencies among groups at all loci. The observed heterozygosities for different groups ranged from 0.625 to 0.9 with an overall average of 0.771. Genetic relationships among groups suggested hierarchical differentiation within cultivated grape. The gene diversity analysis indicated narrow divergence among groups and that most variation was found within groups (approximately 85%). Partitioning of diversity suggested that the remaining variation is somewhat structured hierarchically at different levels of differentiation. The overall organization of genetic diversity suggests that the germplasm of cultivated grape represents a single complex gene pool and that its structure is determined by strong artificial selection and a vegetative mode of reproduction.

Synaptic mutation associated with gametic sterility and population divergence in Coptis teeta (Ranunculaceae)

Cytogenetic investigations of 13 natural populations of Coptis teeta, an endemic and endangered medicinal plant from the Eastern Himalaya, were carried out. About 70–80% individuals in some of the populations were synaptic mutants. The predominantly sexually breeding plant populations were confined to higher cooler latitudes, whereas the mutant apomict inhabited lower warmer latitudes. The breeding systems were observed to be associated with morphological differentiation and ecological preference of some populations. Individuals of subsp. teeta reproduced sexually as well as vegetatively, but those of subsp. lohitensis have adapted almost entirely to a vegetative mode of reproduction. Though no variation was observed in somatic chromosome number and karyotypes, the two subspecies differed significantly with respect to their male meiotic behaviour and rhizome morphology. The mutants either produced little fertile pollen or were completely sterile, leading to low seed production or none at all. This has resulted in low reproductive fitness, localized distribution and small population sizes of the taxon.

Synaptic mutation associated with gametic sterility and population divergence in Coptis teeta (Ranunculaceae)

Cytogenetic investigations of 13 natural populations of Coptis teeta, an endemic and endangered medicinal plant from the Eastern Himalaya, were carried out. About 70–80% individuals in some of the populations were synaptic mutants. The predominantly sexually breeding plant populations were confined to higher cooler latitudes, whereas the mutant apomict inhabited lower warmer latitudes. The breeding systems were observed to be associated with morphological differentiation and ecological preference of some populations. Individuals of subsp. teeta reproduced sexually as well as vegetatively, but those of subsp. lohitensis have adapted almost entirely to a vegetative mode of reproduction. Though no variation was observed in somatic chromosome number and karyotypes, the two subspecies differed significantly with respect to their male meiotic behaviour and rhizome morphology. The mutants either produced little fertile pollen or were completely sterile, leading to low seed production or none at all. This has resulted in low reproductive fitness, localized distribution and small population sizes of the taxon.

Isozyme variation among populations of the clonal species, Phragmites australis (Cav.) Trin. ex Steudel

Few studies have examined population genetic variation in clonal, emergent, aquatic plant species. Phragmites australis (Cav.) Trin. ex Steudel is a clonal, cosmopolitan species common to marshes, estuarine, and other wetland habitats. With the exception of several European studies examining local variation, little is known about the distribution of genetic variation in this taxon, particularly in the U.S. In recent years, the rapid and invasive, vegetative spread of P. australis into disturbed marsh habitats in the U.S., particularly on the Eastern Seaboard and the Mississippi River delta, has sparked interest in its ecology and genetic structure. In this study, electrophoresis was used to analyze isozyme variation among 37 populations of P. australis from the eastern half of the U.S. The electrophoresis data strongly support a primarily vegetative mode of reproduction and spread. A total of 21 multilocus, isozymic phenotypes were identified among the 37 populations. All populations sampled along the Gulf Coast (GC) from Texas to the Florida panhandle (with the exception of the two populations from the Mississippi River delta) were uniform, sharing a single, multilocus phenotype. P. australis populations had lower levels of percent polymorphic loci and number of alleles per locus than typical asexual terrestrial species, but had a higher mean heterozygosity. Nei's genetic distance UPGMA depicts a substantial amount of geographic clustering of populations. However, populations described as `invasive' showed no genetic similarity to one another.

Equisetites arenaceus from the Upper Triassic of Germany with evidence for reproductive strategies

In situ triplet groups of asymmetrical ellipsoidal strobili of Equisetites arenaceus in different stages of maturity, borne at the end of straight equisetalean branches, are described from the Keuper (Upper Triassic) of southern Germany. Apart from the organization of the strobili, spores in situ are also described. The strobili are compared to other equisetalean strobili with in situ spores and to extant Equisetum material. An additional mode of vegetative reproduction by shed twigs indicating adventitious roots is proven. In autochthonous situations, dense packages of shed twigs built up patches of newly sprouted rhizome layers. Moreover, we include Equisetites elegans Kräusel, 1959 in E. arenaceus (Jaeger) Schenk and give an emended diagnosis for the species.

Prothallus Structure in Cladonia

All of the taxa in the lichen genus Cladonia that were examined for this study possess a prothallus. This non-lichenized, exclusively fungal component of the thallus was found in both organic and inorganic substrates. It was usually found in contact with the primary squamule or with another part of the photosynthetic thallus such as the podetium. Most prothallus mycelial aggregations were diffuse. Some formed rhizine-like bundles, aggregations, or non-cellular masses. Most of the species had more than one prothallus form. Secreted materials, which bind the hyphae of the prothallus to one another and to particles of substrate were observed. The prothallus may provide a mode of vegetative reproduction in Cladonia lichens, and it may play a role in soil stabilization. In this study, the genus Cladonia was surveyed in order to describe the prothallus and its characteristics. The prothallus is an exclusively fungal component of the lichen thallus, in which contact with the algal photobiont is infrequent. The prothallus is contiguous with the photosynthetic lichen thallus, but it is found beneath the surface of the substrate. It has a characteristic fungal morphology, in which tubular, elongated hyphal cells ramify, anastomose, and aggregate into various configurations. Most lichens possess a prothallus, and the prothallus is conspicuous in many humicolous and saxicolous species Letrouit-Galinou & Asta 1994; Sanders 1994). All of the major morphological groups crustose, foliose, fruticose, and squamulose lichens, possess taxa with a prothallus. In most of the species of Cladonia and in the genus Cladina the prothallus is inconspicuous but in species of section Cocciferae it is macroscopically visible and conspicuous. Prothalli were present in all of the species that were studied here. Vainio (1887, 1894, 1897) described the prothallus in the species that he included in his monograph. He proposed that the prothallus (or hypothallus) might function as an anchor to the above ground thallus, or that it might translocate materials to the lichenized thallus. He also considered the potential role of the prothallus in dispersal and vegetative reproduction. Krabbe (1891) described the process by which the fungal component of Cladonia came into contact with algal cells, producing a lichen thallus. Zuckel (1896) described the wandering in Peltigera venosa (L.) Hoffm. and Solorina saccata (L.) Ach., in which the fungal mycelium forms rhizines that run horizontally through the ground, producing new thalli. Gallee (1913, 1920, 1954) applied the concept of hypothallus wanderer to questions of dispersal and reproduction in Cladonia. He suggested that the prothallus might provide the lichen with the ability to exploit new habitats outside of its immediate microenvironment. He contrasted two morphologies in the prothallus and attributed taxonomic importance to them. He distinguished between diffuse prothalli, and prothalli with thick hyphal bundles devoid of intercellular spaces. Both of these forms and their intermediates were found in the present study. Hannemann (1973) illustrated the prothallus rhizomorphs of a few Cladonia species and described them as rhizoptes or Rhizinenstriigen, (rhizine-strands), a term later used by Ott et al. (1993). Thogersen (1977) illustrated the prothallus of Cladonia macrophylla (Schaer.) Stenh., but no explanation was provided with the illustration. Jahns (1988) suggested that the prothallus might serve to attach the thallus to its substrate and in addition, might function in water and mineral uptake. Ahmadjian (1993) briefly discussed mycelial growth in Cladonia and suggested that the prothallus might be a free-living symbiont with a potential role in the establishment new lichen colonies. Ott et al. (1993) concluded that the hyphae of the prothallus are reservoirs or conduits for subsurface moisture. Hammer (1996) discussed the role of the prothallus as a soil stabilizer in lichen-dominated habitats. The genus Cladonia was surveyed here in order to describe the prothallus and its characteristics. MATERIALS AND METHODS Approximately 500 specimens in the genera Cladina, Cladonia, and Trapeliopsis were examined for the present study. The specimens were obtained from fresh collections that were not curated or from herbarium specimens at the Farlow Herbarium (FH). Connections with the photosynthetic thallus were confirmed by dissection. The speci0007-2745/96/212-217$O.OO/O This content downloaded from 207.46.13.51 on Sun, 19 Jun 2016 06:07:04 UTC All use subject to http://about.jstor.org/terms 1996] HAMMER: FUNGAL AGGREGATIONS 213 C,,rCl;t, 2---~-~ ,, I / : 9L: Y1 ?L `4 L~E~V `\?

Recent Progress in the Systematics of Basidiomycetous Yeasts

Basidiosporogenous yeasts and basidiomycetous anamorphic yeasts have been classified based on the morphological, physiological and biochemical characteristics. Higher taxonomic ranks such as genus, family etc. are classified based on the mode of vegetative reproduction, morphological characteristics found during sexual reproduction and certain physiological characteristics such as the assimilability of inositol. Recent chemosystematics studies suggest the unreasonableness of the taxonomic system based on these characteristics. Monosaccharide compositions of the cells, especially the presence or absence of xylose, and ubiquinone systems are suggested to be more reliable systematic criteria than the mode of vegetative reproduction and morphological criteria found during the sexual reproduction on the basis of the partial sequencing study of rRNAs. Ultrastructural features well correlate with chemosystematics characteristics and are regarded as reliable systematic criteria in higher taxonomic ranks. Polyphasic approaches are essential for further progress of the systematics of basidiomycetous yeasts.

Evaluation of phylogenetic relationships among fission yeast by nDNA/nDNA reassociation and conventional taxonomic criteria

The genus Schizosaccharomyces comprises a small, somewhat heterogeneous group of yeast species which have in common a unique mode of vegetative reproduction by cross-wall formation without constriction as well as a certain degree of osmophilia, most strains having been isolated from habitats of high sugar concentration. This study evaluated inter- and intraspecific relationships utilizing nDNA/nDNA optical reassociation and by the analysis of physiological profiles of several strains of each species. Results demonstrate that the genus should be divided into three species: Schiz. japonicus, Schiz. octosporus and Schiz. pombe.

A Photoperiod Determined Life-Cycle in an Oligochaete Worm

For one common cosmopolitan naidid worm, Stylaria lacustris, we studied the effects of different environmental factors upon (1) the alternation of reproductive modes, (2) the rates of population increase, and (3) the combination of each of (1) and (2). While age, temperature, population density, or rate of feeding did not affect the mode of reproduction, photoperiod had a dominant effect. Under long-day conditions (LD > 12: 12), all worms reproduced exclusively by paratomic fission, theoretically ad infinitum. When transferred to short-day conditions (LD {le} 12:12) the worms ceased vegetative reproduction, and within 2 to 4 weeks developed the hermaphroditic genital apparatus and a clitellum. After an additional two weeks, the first cocoons were produced. The switch to the bisexual mode of reproduction was cum grano salis irreversible. These findings are consistent with observations of field samplings, and allow one to predict the annual life-cycle strategy of S. lacustris. This is the first example of a photoperiod determined life-cycle within the oligochaete worms. The vegetative mode of reproduction led to extremely high rates of population increase, whereas with the bisexual mode of reproduction the number of individuals was roughly stable. However, because S. lacustris could not withstand temperatures of 5{deg}C or lower, the switch to sexual reproduction and the formation of diapausing cocoons appear to be the only mechanism of overwintering. Nevertheless, some `asexual' clones never switch to sexual reproduction, whereas a loss of the asexual vegetative mode of reproduction did not occur. In contrast to some general predictions from life-history theories, the reproductive strategy of S. lacustris is highly preprogrammed and cannot respond to sudden and unexpected environmental changes.

The Contrasting Dynamics of Two Populations of Plantago Lanceolata Classified by Age and Size

(1) The dynamics of two populations of Plantago lanceolata from contrasting habitats are simulated with the use of matrix projection models. The fecundity and survival parameters that together form the matrix are based on demographic fieldwork and evaluated for both size and age categories at the same time. (2) After verification of the model, elasticity analysis is applied to determine the model parameters that are most important in defining the population growth rate. The effect of more complex changes in the life histories on the population growth rate is evaluated by means of simulation. (3) The results are in general agreement with expectations based on field observations: seed production is more important in an unpredictable environment, whereas adult survival is more important in a stable environment. In both populations seedling establishment is the most important phase in the life history, especially in the stable habitat. (4) The formation of side rosettes is not so much a mode of vegetative reproduction as a way to increase the current year's seed production in an unpredictable environment. (5) Timing of germination in spring or in autumn is important, but the effect of delay by means of a seedbank is unexpectedly small. (6) The particular form of this matrix projection model is time-invariant. Because fecundity and survival are rarely constant over time, however, random sequences of bad, normal and good years are generated and incorporated in the model. The impact of this variation over time is evaluated using time-to-extinction as a measure.

Effects of Experimental Releases of Oil and Dispersed Oil on Arctic Nearshore Macrobenthos. III. Macroalgae

An experimental subsurface release of chemically dispersed oil at Cape Hatt, northern Baffin Island, resulted in short-term relatively high oil concentrations in the water of two adjacent bays. Untreated oil released onto the surface of the third bay could not be detected in the water below a depth of 1 m. Both releases, however, resulted in measurable contamination of sediments in shallow water. Macroalgae at 3 m depth were sampled by a diver-operated airlift sampler in three treatment bays and in a fourth (reference) bay during the open water seasons of 1980-83 (two pre-spill and four post-spill sampling periods). Biomass, number of species and reproductive condition of the dominant understory algae at 3 m depth did not seem to be adversely affected wither by oil in subtidal sediments or by chemically dispersed oil in the water column. No oil effects were detected in data on the biomasses of total algae or of two of the three species analyzed (Stictyosiphon tortilis and Pilayella littoralis). In the third species, Dictyosiphon foeniculaceus, growth increased in the year following the oil release, either stimulated by low levels of oil in sediments or through natural annual variability. The lack of major effects on macroalgae may have been partly attributable to the lack of effects on herbivores and the vegetative mode of reproduction in the dominant macroalgal species.Key words: arctic macroalgae, oil effects, dispersed oil effects, experimental oil releases, Baffin Island, macrobenthos, Stictyosiphon tortilis, Pilayella littoralis, Dictyosiphon foeniculaceus

Root Formation by Stems of Eucalyptus botryoides Sm. In Natural Stands

The production of new shoots from dormant bud strands in eucalypt stems is a well documented and important adaptive trait of most species. The production of roots by stems of naturally occurring eucalypts and the associated adaptive significance of this phenomenon are poorly documented. This paper reports both field and glasshouse observations on the production of roots by coppice and lignotuber stems and fallen main stems of Eucalyptus botryoides Sm. Transverse sectioning of stems at sites of root initiation showed that the area immediately surrounding the root was comprised of aerenchyma tissue. The production of new shoots and roots by the various types of E. botryoides stems constitutes a mode of vegetative reproduction that may be vital for the persistence of this species in the harsher parts of its environmental range. A summary is provided of the taxonomic groupings of all eucalypts that have produced roots from stems under a range of field environments.

Cytological studies on three aquatic members of hydrocharitaceae in relation to their morphological and ecological characteristics.

The present investigation has included the study of the morphological and cytological details of seventeen populations of three aquatic submerged taxa viz. Hydrilla verticilla Presl., Ottelia alismoides Pers. and Vallisneria spiralis L. belonging to the family Hydrocharitaceae. The species examined were collected from various localities in the plains of West Bengal.The chief objective was to analyse the nature of association among different environmental factors, morphological variations and chromosomal peculiarities.Morphological details, giving average leaf length and breadth and length of internodes, were observed in members of each population and the average calculated. Karyotype analysis was carried out on each population following pretreatmentorcein squash technique modified for the purpose. The pH and proportions of Ca, Mg, K and Na were calculated of the aquatic medium surrounding each population.Eight populations of H. verticillata were studied. Seven show 2n=24 chromosomes while only one population has 2n=16 chromosomes. The karyotype formulae were observed to differ significantly.The water analysis data indicated a wide range of variation in the proportions of minerals and of pH. No direct association among the morphology, water analysis data and the chromosome numbers was noted.Four populations of Ottelia alismoides studied showed chromosome numbers 2n=44, 66 and 68. The populations with same chromosone numbers differ from each other in the structural composition of chromosomes. Population III (2n=68) is an aneuploid one which may have arisen through duplication of two chromosomes from a 2n=66 type or from 2n=33 type following duplication of the entire genome. The tetraploid populations I and II have a total chromatin length less than double those of III and IV indicating a diminution in chromosome size with polyploidy.The water analysis data indicates that the species can tolerate wide chemical variations in their aquatic environment.In the five populations of Vallisneria spiralis the chromosome number is 2n=30 for populations I and III, 2n=40 for II and V and 2n=24 chromosomes for IV. Karyotypes differ even among the populations with same number. Total chromatin length shows a proportionate increase during polyploidy.Populations II and V with 2n=40 chromosomes have apparently evolved through polyploidy followed by structural changes in the chromosomes. Population IV represents a completely different picture. Its chromosome number may have been derived from 2n=40 or 2n=30 forms through non-disjunction and maintained through vegetative propagation.There is no apparent association between the minerals present in the aquatic media and the chromosomal composition of the populations. The only exception is population IV.The observations show that cytological races cannot be correlated with morphological characteristics. The water analysis data can suggest no specific association between the morphological and cytological characteristics, except that an alkaline medium of range of 6.8 to 8.55 is necessary.In all the taxa studied vegetative mode of reproduction is an important factor of propagation. The occurrence of variant nuclei in the somatic cells indicates the way through which a new form could have arisen in nature. Such a variant nucleus, on entering a growing shoot, may give rise to a cytologically different form which may later form a colony under environmental conditions best suited for its survival. The excess of nutrients present in the surrounding media may permit all these forms to survive.As far as the present study shows the alkalinity and mineral content do not have any definite effect on the evolution of cytological races. A possible role of the supply of nutrients through soil and of light intensity can be suggested.