The Structure and Development of the Thallus in the British Species of Gelidium and Pterocladia

The apical structure and the development of the thalli of allthe British species of Gelidium and Pterocladia have been investigated;the development of G. pulchellum is described in detail. Eachaxis is terminated by one or more apical cells, which by theirsegmentation form the tissues of the thallus. An axial filamentis distinct for a short distance behind each apical cell, butsecondary pit-connexions develop rapidly so that in sectionthe mature axis has the appearance of a multi-axial structure. Lateral branches of the frond develop by the segmentation ofthe lateral branch apical cells, which are formed by the transformationof superficial cortical cells, either in the meristematic ormature parts of the axes. The extreme variability of externalappearance is due principally to the indeterminate origin ofall lateral branches. The thallus in the British species of Gelidium and Pterocladiaconsists of erect fronds borne on creeping axes. The relativeproportions of the frond and creeping axes in various speciesand their survival through adverse conditions are discussed.     

The Life-History of Marginariella urvilliana (Ach. Rich.) Tandy

In Marginariella urvilliana gametes are produced in the thirdyear and then annually for several years. On germination ofthe egg a single primary rhizoid is formed. Its early subdivisioninto four main branches is unusual amongst the Fucaceae. Growthof both the main axis and of the receptacles is carried outby a three-sided apical cell. The oogonia develop earlier thanthe antheridia. Nuclear divisions are completed within the conceptacle,often several weeks before extrusion of oospheres. The liberatedoosphere is held in a tubular stalk until after fertilizationand the sporeling has begun to develop. Marginariella has affinities with the other endemic submergedAustralasian fucoids, and together these form a rather isolatedgroup, probably rightly included within the Fucaceae.     

Analysis of Branching in Spring-sown White Lupins (Lupinus albusL.): The Significance of the Number of Axillary Buds

Plant density and sowing date were shown to affect branchingin spring-sown white lupin (Lupinus albusL.), but the responsevaried among environments. The patterns of primary and secondarybranching in the cv. Lublanc were studied as a function of boththe number of axillary buds and the plant growth rate. Fieldexperiments that used a wide range of sowing dates and plantdensities to alter plant architecture were conducted over 5years, and these were supplemented with data from additionalglasshouse and growth cabinet experiments. The number of axillary buds on the main stem or primary branches,which determined the potential number of branches, increasedlinearly with the number of nodes. In situations where all axillarybuds did not produce branches, it was found that the numberof primary and secondary branches produced was related to theplant growth rate at the beginning of branch elongation. Knowledgeof the number of axillary buds improved the analysis of theinteraction between cultural practices and environmental conditionson plant architecture. The variability of branching potentialamong genotypes was discussed. Lupinus albus; branches; axillary buds; growth; sowing date; plant density     

Genetic Variability ofLepidium meyeniiand other AndeanLepidiumSpecies (Brassicaceae) Assessed by Molecular Markers

A phylogenetic survey based on similarity levels was performedfor 29 cultivated accessions of maca (Lepidium meyeniiWalp.)and 27 accessions of wild species ofLepidiumfrom Ecuador, Peruand Bolivia, with RAPD markers. Chromosome counts for each accessionwere also performed. The similarity tree matrix separated intwo main branches: cultivated and wild species. The similaritylevel among cultivated accessions was high (0.952 or higher)indicating a low level of polymorphism. Within the wild species,two main secondary branches could be resolved, of which onewas subdivided into two tertiary branches. Morphological evaluationof the wild species accessions within each main group identifiedthree wild species: (1)L. bipinnatifidum, consisting mostlyof tetraploids and a single octoploid accession; (2)L. kalenbornii,consisting only of tetraploid accessions; and (3)L. chichicara,consisting mostly of octoploid and a few tetraploid accessions.Clustering by principal coordinates analysis supported the resultsobtained by the similarity tree matrix. These results indicatethat none of the three wild species is related enough to beconsidered ancestral to the cultivatedL. meyenii. Three accessionsof intermediate position may be of hybrid origin. None of thewild species was found to be diploid, which suggests that polyploidyhas been an important adaptation to high altitude habitats inthese species.Copyright 1998 Annals of Botany Company Lepidum meyenii, Lepidium peruvianum, maca, DNA markers, phylogeny.     

Cytological Investigations on Porphyra umbilicalis(L.) Kutz. var. laciniata(Lightf.) J.Ag.

1. Vegetative mitosis of Porphyra umbilicalis var. laciniatais normal, the chromosome number as seen in late prophase beingfive. Special features of this mitosis are the appearance ofseveral stained chromatin segments in early pro-phase and theformation of a crescent-shaped group of chromosomes during metaphaseand anaphase. 2. Genuine monospores have not been seen in the material investigated. 3. Both spores and spermatia arise by repeated division of amother-cell and in identical ways. Evidence is presented toshow that the first division in the mother-cell forming sporesis longitudinal. There is no evidence of reduction divisionin this division, and the chromosome number in the mother-cellis five. 4. The first division in the germinating spore is mitotic andshows five chromosomes. 5. The Conchocelis-phase is haploid throughout and produces‘fertile cell rows’ and ‘plantlets’,but spore liberation has not been observed. It is suggestedthat the ‘plantlets’ may grow out directly intothe leafy phase or may give rise to spores according to prevailingenvironmental conditions. 6. No evidence of sexual reproduction has been obtained in thepresent work and the role of the spermatium in the life-cycleis not clear. It is suggested that further work may profitablybe concerned with investigating the nature of the spermatium.     

Pattern of Shoot Growth in Zizyphus mauritiana and Z. oenoplia

Shoot polymorphism and patterns of sylleptic branching and shoottip abscission in two Zizyphus species are reported. Z. mauritiana(ber) produced three types of proleptic shoots: vigorous, normaland spur-type, by reiteration or following pruning;Z. oenopliahad only one type of shoot. Both species revealed up to thirdorder sylleptic branching on the vigorous proleptic shoots witha characteristic pattern and rhythm. Bud dormancy breaking chemicalsgiven as pre-pruning foliar sprays in ber, did not alter thepattern of sylleptic branching. Zizyphus oenoplia produced morefirst and second order sylleptic branches compared to Z. mauritiana.All main axes and 97% of first order sylleptic branches ofZ.mauritiana abscised their apical buds during summer, but inZ. oenoplia all main axes and 54% of first order sylleptic branchesremained active. Shoot tip abscission was almost complete onthe higher order sylleptic branches of both species. Activefirst order branches in Z. oenoplia were confined to the tophalf of the shoot. Both species had a few dormant apical budsduring the summer on their sylleptic branches, emerging mostlyfrom the middle portion of the shoot. Some of the most vigorousfirst order branches of Z. oenoplia, which had dormant apicalbuds during summer, showed a change in the frequency of syllepticbranching when they resumed growth following monsoon showers.These characteristic growth and branching patterns may haveadaptive value for canopy development under arid and semi-aridconditions. Copyright 1999 Annals of Botany Company Ber, branching pattern, shoot polymorphism, shoot tip abscission, sylleptic branching, Zizyphus mauritiana, Zizyphus oenoplia.     

Influence of Endomycorrhizal Infection on Root Morphology in a Micropropagated Woody Plant Species (Vitis vinifera L.)

The influence of vesicular-arbuscular (VA) endomycorrhizal infectionon root morphology and architecture of a woody micropropagatedplant, Vitis vinifera L., has been investigated using morphologicalanalysis, modelling and topological methods. Endomycorrhizaformation caused increases in lateral root number and consequentlytotal root length but did not alter the number of root axes.The rate of production of any order lateral roots was higherin mycorrhizal than non-mycorrhizal controls. The number offirst- and second-order laterals increased linearly with timein mycorrhizal plants whilst in control plants both fitted alogistic function. Topological analysis indicated similar patternsof root branching in the early stages of growth, but the rootsystem of non-mycorrhizal plants adopted a more herringbonepattern after 8 weeks, whereas that of mycorrhizal plants retaineda more dichotomous pattern with repeated bifurcation. Althoughthe root system pattern of non-mycorrhizal vines is more efficientin exploring soil, it is more expensive for the plant in termsof energy cost versus return benefit (nutrient acquisition).In contrast mycorrhizal plants develop a more economical rootsystem which is rendered more efficient by the direct role ofthe mycorrhizal fungus in assisting nutrient absorption. Vitis vinifera L., vine, root system, modelling, topology, vesicular-arbuscular mycorrhizae     

OXYNOE AZUROPUNCTATA, N. SP., A NEW SACOGLOSSAN FROM THE FLORIDA KEYS (MOLLUSCA: OPISTHOBRANCHIA)

A new species of Oxynoe from the Florida Keys is described.It differs from the other Caribbean Oxynoe, O. antillarum Mörch,1863, in color, number and size of papillae, size increase ofradular teeth, diet, and type of development. The type of developmentis extended lecithotrophic. The larvae hatch about 4 weeks afterthe eggs have been deposited, and metamorphosis is completedafter about one additional week. Oxynoe azuropunctata n.sp.feeds on Caulerpa paspaloides, C. cupressoides and C. sertularioides.Details of the feeding process in Oxynoe are described for thefirst time. The junction of the oral tube and the pharynx isequipped with a complex muscular buccal apparatus, part of whichis everted during feeding. The protrusible parts of the buccalapparatus completely surround part of an algal filament, whichis then slit with the radula, and the cell sap is sucked out.The protrusible parts are retracted after the filament has beenreleased. ^*Present address: Ellebjergvej 22, 1 t.h., DK-2450 CopenhagenSV, Denmark (Received 13 November 1979;     

Stand Density Effects on Branching in an Annual Legume (Senna obtusifolia)

Effects of proximity to nearest neighbours on shoot morphologyand branch growth were examined for Senna obtusifolia (L.) I.& B., an annual legume species that displays wide variationin branching. Periodic surveys described location and type ofgrowth at all nodes on plants in regularly spaced monocultures.Stands with interplant distances of 15-50 cm (51-5 plants m^-2)formed closed canopies with similar amounts of leaf area andbiomass. Number of lower primary branches, their degree of curvature,and location of branch apices relative to the main stem respondedto interplant distance relatively early in shoot growth, beforecanopy closure. The final effects of ten-fold differences inplanting density on the formation of these ascending lower brancheswere only two-fold differences in number of vertical shoot axeswithin the stand. An additional study examined response of lowerbranches to an adjacent gap in the stand. Initial number anddirection of branch growth were not affected by location ofthe gap. The first effect of crowding by neighbours was on number ofbranches initiated by developing shoots. Differences in branchingsubsequently increased through differentiaI survival and directionof branch growth. Such alterations principally affected lateralexpansion of individual shoots, with little effect on radialsymmetry or vertical distribution of leaves.Copyright 1994,1999 Academic Press Branch morphology, canopy, competition, light quality, Senna obtusifolia, shoot growth, sicklepod     

Studies in the Bangioideae III. The Life-history of Porphyra umbilicalis (L.) Kutz. var. lociniata (Lightf.) J. Ag.: A. The Conchocelis-Phase in culture

As the first step in an investigation of the life-history ofPorphyra umbilicalis (L.) Kütz. var. laciniata (Lightf.)J. Ag., spores which have originated as a result of the repeateddivision of the mother-cells have been germinated. When grownon glass their method of germination and growth agrees withthat described by previous investigators, but when germinatedon sterile shell the germ-tubes penetrate the shell and developinto growths identical with Conchocelis rosea Batters. This‘species’, therefore, is a phase in the life-historyof P. umbilicalis var. laciniata and not an autonomous species.The development of the ‘Conchocelis’-phase in cultureis described and also the formation of fertile cell-rows and‘plantlets’. Until the significance of these structuresis understood and a cytological investigation completed, therelationship of the intertidal leafy Porphyra-thallua to thefilamentous, shell-inhabiting, deep-water Conchocelis cannotbe expressed in the terms usually employed to denote the variousphases of the life-histories of algae.     

The Growth and Reproductive Cycle of Pleurozium schreberi (Brid.) Mitt

The reproductive cycle of the moss Pleurozium schreberi hasbeen investigated by scoring over 600 specimens from Britainand elsewhere, and through regular observations on several populations.P. schreberi is at least functionally dioecious and the stemsare perennial, producing all the inflorescences of a given cycleduring the autumn. On male plants perigonia develop in largenumbers, principally on lateral branches. Relatively few perichaetiaare formed on female stems where they are largely confined tothe main axes. In Britain perigonial development begins in August,the antheridia remaining in the immature stage during the winterresting phase. Young perichaetia are first recorded in Octoberand the archegonia overwinter in the juvenile stage. Rapid gametangialdevelopment takes place in spring prior to the main fertilizationperiod in April and May. Young sporophytes are present fromMay onwards. Setal elongation is delayed until August, but thelate operculum intact stage is reached by October. In Britainthe spores are shed between January and April, nine to twelvemonths after fertilization. Data from the literature and fromFrench, Finnish, and North American specimens suggests a similarcycle in other areas, though with slight differences, notablythat fertilization in parts of Scandinavia may be delayed comparedwith Britain. The results from periodic measurements of marked plants andother techniques suggest that in Britain vegetative growth mayalso show a winter resting phase, stem elongation being recordedonly from April to November.     

DUDRESNAYA PATULA SP. NOV., AN UNUSUAL DEEP-WATER RED ALGA FROM FLORIDA1

Dudresnaya patula sp. nov. is described from 30–60 m depth on the east coast of Florida. The plant grows to a height of at least 10 cm, has flattened axes and main branches to 2 cm wide and 3 mm thick, and has unusually long female reproductive branches. The new species is compared to other Dudresnaya species in habitat, vegetative structure, and reproductive morphology.     

Acclimation of Respiratory Properties of Leaves of Spinacia oleracea L., a Sun Species, and of Alocasia macrorrhiza (L.) G. Don., a Shade Species, to Changes in Growth Irradiance

To clarify the way in which the light available for growth affectsrespiration in leaves of sun and shade plants, we examined therespiratory properties of mature leaves of Spinacia oleraceaL., a sun species, and of Alocasia macrorrhiza (L.) G. Don.,a shade species, that had been grown at various irradiances.In leaves of S. oleracea, the respiratory rates, on a dry massbasis, decreased with time during the night, and the higherwas the growth irradiance during the day, the higher was therespiratory rate. The marked decreases in the respiratory rateduring the night were accompanied by decreases in the concentrationof carbohydrates in the leaves. By contrast, the respiratoryrates of leaves of A. macrorrhiza were virtually constant throughoutthe night and the absolute rates were lower than those of S.oleracea even though the absolute value of the concentrationof carbohydrates and its decrease at night resembled to thosein S. oleracea. The maximum activities of respiratory enzymeswere also similar to those in S. oleracea. However, the leavesof A. macrorrhiza contained less soluble protein than thoseof S. oleracea. These results suggest that, in S. oleracea,the concentration of carbohydrates might determine the respiratoryrate while such is not the case in A. macrorrhiza. The lowerrespiratory rates in A. macrorrhiza might be due to a lowerdemand for ATP. (Received November 29, 1995; Accepted February 15, 1996)     

The Distribution of Silicon Deposits in the Roots of Molinia caerulea (L.) Moench. and Sorghum bicolor (L.) Moench.

The occurrence of silica in relation to meristematic zones andthe thickening of the endodermis in the roots of Molinia caerulea(L.) Moench. and Sorghum bicolor (L.) Moench. has been investigatedby means of the electron-probe microanalyser and the scanningelectron microscope. In proximal regions of mature roots ofM. caerulea, the central strengthening tissue of the stele,the vessel walls, the endodermis and the sub-epidermal sclerenchymaare areas of heavy accumulation. The distal regions of suchroots are relatively free of silicon and show little thickeningof the inner tangential walls of the endodermis or of the cellsof the strengthening tissues. The thickening of these elementsis shown to be associated with their location and the age ofthe root. In the proximal regions of S. bicolor, silicon is detected andlargely confined to the inner tangential walls of the endodermiswhich display some thickening. In addition, discrete and evenly-distributeddeposits varying in size partly fill the lumen of this layer.Some cells exhibit a number of smaller protrusions. High magnificationsof these lumen deposits show a distinct granular structure incontrast to the very uniform pattern of the wall deposits. The results are compared with deposits in grass leaves and inflorescencebracts and in woody perennials. The presence of silicon in additionto suberin, lignin and polyphenols in the thickened endodermalwall is also discussed in relation to the recognized functionof the endodermis.     

Description and Model of the Architecture of Four Genotypes of Determinate Autumn-sown White Lupin (Lupinus albus L.) as Influenced by Location, Sowing Date and Density

The structure of four new autumn-sown determine genotypes ofwhite lupin, grown with a combination of sowing dates and plantdensities at four locations in France was studied in 1990/91and 1991/92. Plant architecture was characterized in terms ofthe number of first-order branches produced and the distributionof leaves on these branches and how they varied with the numberof mainstem leaves and the position of the branch on the mainstem. The variation in the number of mainstem leaves on determinegenotypes was satisfactorily described by an earlier model developedfor indeterminate genotypes using the intensity of vernalizationrelative to accumulated temperature above 3°C as input.However the architecture of the first-order branches, definedby their number and the total number of leaves per branch ateach subtending position on the mainstem, differed and was influencedby genotype, location and sowing date. In four determinate genotypes,these two characters were positively correlated, and correlatedwith the number of leaves on the mainstem. Increasing densityfrom 10 to 40 plants m^-2 reduced the number of branches andtheir total number of leaves. Pruning 15 leaves from the mainstemat the beginning of stem elongation did not influence the developmentof the first-order branches. There appeared to be a functionalrelationship between the number of leaves on the mainstem andthe number of branches established very early in the growingseason. The profiles of number of leaves on the first-order brancheson the mainstem with branch position were modelled using twosub-models, one describing the mean number of leaves on thebranches actually present, and the second describing the frequentlyof occurrence of a branch at a particular position on the mainstem.Of the five model parameters, one, representing the minimalnumber of branches present on the plant, was correlated withthe number of first-order branches. Genotype, location, sowingdate and density affected the shape of the profiles.Copyright1993, 1999 Academic Press While lupin, Lupinus albus L., determine growth, architecture, model, branch     

Winter Growth of Autumn-sown White Lupin (Lupinus albus L.) Main Apex Growth Model

The winter growth of winter white lupin (cv. Lunoble) was investigated.Over three consecutive years, 1987–1989, it was sown atdifferent times at Lusignan (France) and in 1989, at nine differentlocations with various sowing times. The production of primordia,the vernalization requirements and the final number of leaveson the main stem were related to field measurements of dailymaximum and minimum temperatures. A statistical model for the main apex growth with a system oftwo equations was developed, with a threshold level for leafprimordia production at 3 °C. The number of leaf primordiaproduced by a vegetative apex (y) in terms of the cumulativesums of temperature over 3 °C (x) followed the curvilinearregression y = 4.76 + 00268x + 00000156x². The upper and lowertemperature limits for vernalization were estimated as 14 andI °C respectively. The vernalization requirements of a vegetative apex (y) decreasedwhen the number of initials produced (x) increased accordingto the negative exponential regression y = exp (7.2 + 002626.x). The two equations were used for the prediction of the finalnumber of leaves of a lupin crop. The predictive accuracy ofthe model was checked against independent data. The agreementbetween observed and predicted final leaf number was often close,but some deviations did occur with low leaf number. The modeldescribed most of the growth phenomena which occur during thephase sowing to floral initiation of the main stem of a winterlupin crop, and its possible uses are discussed. Lupinus albus L., white lupin, growth, model, vernalization, primordia, apex, thermal time     

Transfer of Pterosiphonia pumila Yendo to the genus Symphyocladia (Rhodomelaceae, Rhodophyta)

The red alga Pterosiphonia pumila Yendo (Rhodomelaceae, Ceramiales) has flattened thalli in which there is complete lateral fusion between branches and their parental axes during early stages of development, the laterals only becoming distally free in reproduc-tively mature plants. This results in a leaf-like organization distinct from that displayed by all other species of the genus Pterosiphonia, the members of which have terete to compressed axes that are congenitally fused along only a few (<4.5) proximal segments of the laterals. The organization of P. pumila is, thus, similar to that of species of the genus Symphyocladia, to which it is here transferred as Symphyoctadia pumila (Yendo) Uwai et Masuda, comb. nov. Symphyoctadia pumila is restricted to Japan and Korea and is distinguished from the other three described species of Symphyocladia by its small (<3 cm long) ecorticate thalli and complete lack of vegetative trichoblasts. Symphyoctadia pennata Okamura has a similar suite of characteristics, has been successfully cross-bred with S. pumila in laboratory culture and is, thus, placed in synonymy with S. pumila.     

Deterination of Effective Partition Coefficients of Alkali Chlorides by Measurements of Concentration Potential across the Nitella flexilis (L.) Ag. Isolated Cell Wall

We report a study in which we estimate by means of non-equilibriumprocesses the value of an effective partition coefficient, x,a parameter that we use to take into account the non-ideal behaviourof the electrolyte of the external medium in the cell wall space.This parameter is defined by the ratio of the salt partitioncoefficient to the activity of the non-diffusing charges. Tothat purpose, concentration potential in NaCl, LiCI and CuCl₂solutions was measured across an isolated cell wall of Nitellaflexilis at different pH. No significant difference appearedbetween the potential values measured in the presence of NaClor LiCl (pH 5.5, 4.0 and 3.0). At pH 3.0, in CuCl₂ solutions,the Nitella wall behaved as an uncharged membrane. Two methods—high concentrations and least-squares approximation-wereused to calculate from these results the value of the effectivepartition coefficient. Both gave similar values of x At a givenpH, the values of x are independent of the concentration ofthe external medium over a large range of concentration ratios.The activity of the exchange sites was estimated by the experimentallydetermined fraction of absorbed monovalent cations. The ionicconcentrations in the wall space were calculated at pH 5.5 and3.0 by introducing the values of x in the relations which correlatethem to the ionic concentrations in the wall for that givenvalue of the activity of the carboxylate sites. From their values,it appears that the negative fixed charges of the wall werefunctionally shaded by the condensation of a part of the adsorbedmonovalent cations. The activity of the former was, therefore,reduced to a value considerably lower than that estimated bythe cationic exchange capacity during equilibrium processes. Key words: Nitella flexilis (L.) Ag., cell wall, concentration potential, partition coefficient, ion condensation