Nature of 'Pollinator' Effect in Potato (Solanum tuberosum L.) Haploid Production

Haploids (2n =24) of the common tetraploid (2n=48) potato (SolanumtuberosumL.) provide promising material for attacking many problemsconcerned with the genetics, cytogenetics and breeding of thisspecies. Interspecific 4xx2xcrosses betweenSolanum tuberosumgp.Andigenaorgp.Tuberosumcultivars as pistillate parents andSolanum tuberosumgp.Phurejaassource of pollen (hereafter ‘pollinator’) have beenused to produce maternally derived haploids through parthenogenesis.This paper discusses the nature of the ‘pollinator’effect in haploid extraction. The ‘pollinator’ hada significant effect on haploid frequencies following 4xx2xcrosses.The ‘pollinator’ effect seems to operate via theendosperm, in which haploid (n=2x) embryos are associated withhexaploid endosperm. A superior ‘pollinator’ appearsto have its effect by contributing two haploid (n) gametes tothe central cell. 2n pollen; double fertilization; endosperm; ploidy manipulations; Solanum tuberosum     

Influence of Irradiated Pollen on Embryo and Endosperm Development in Kiwifruit

Development of seeds following pollination with irradiated pollenwas studied inActinidia deliciosa(kiwifruit) ‘Hayward’.Pollinations were carried out using two different sources ofpollen (‘Tomuri’ and ‘Matua’) irradiatedwith gamma rays at doses of 700 and 900 Gy. Non-irradiated crosseswere used as controls. Pollen irradiation had little effectonin vitropollen germination. Irradiated pollen affected seedset and seed content, and induced the formation of parthenogeneticembryos. In comparison to the control, the embryo growth ratewas slower and the endosperm contained very low amounts of storageproducts. Seed set was significantly reduced following bothdoses of irradiation. Two types of seeds were observed: (1)seeds with endosperm only; and (2) seeds with both embryo andendosperm. The proportion of seeds containing endosperm onlywas almost ten-fold higher than those containing both embryoand endosperm. Embryo production by gamma-irradiated pollenwas genotype- and dose-dependent. The induction of parthenogenesiswas higher following gamma ray doses of 900 Gy than 700 Gy,which suggests the ‘Hertwig Effect’; the best efficiencywas obtained with ‘Tomuri’ pollen. Ploidy levelof parthenogenetic embryos was evaluated by nuclear size (area)with the use of image analysis. There was a large differencein embryo nuclei size between control and parthenogenetic embryos(mean size 90.8 and 49.1 µm², respectively). It is concludedthat parthenogenetic embryos represent trihaploids.Copyright1998 Annals of Botany Company. Actinidia deliciosa, kiwifruit, pollen irradiation, induced parthenogenesis.     

Investigations on the Control of Lettuce Seed Germination at High Temperatures

The activity of sodium hypochlorite solution in relieving thermo-inhibitionof germination of lettuce seed is shown to be due to its chlorinecontent. Results of experiments in which the pericarp, and pericarpand endosperm were removed, together with direct measurementsof penetration forces, suggest that the relief of thermo-inhibitionresults from weakening of the pericarp by the hypochlorite.Differences between the cultivars ‘Cobham Green’and ‘Grand Rapids’ in the contributions made bypericarp and endosperm to germination control at 35 °C aredemonstrated. Key words: Lactuca sativa L, Chlorine, Thermo-inhibition     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

Developmental Genetics and Morphological Evolution of Flowering Plants, Especially Bladderworts (Utricularia): Fuzzy Arberian Morphology Complements Classical Morphology

This review compares new developmental models on flowering andother vascular plants with evolutionary hypotheses formulatedby Agnes Arber (1879–1960) and like-minded botanists.Special emphasis is laid on philosophical basics such as perspectivism,pluralism about evolutionary modelling, continuum way of thinking,and fuzzy logic. Arber's perspective is best labelled as F uzzyA rberian M orphology (FAM Approach). Its proponents (‘FAMmers’)treat structural categories (e.g. ‘roots’, ‘shoots’,‘stems’, ‘leaves’, ‘stipules’)in vascular plants as concepts with fuzzy borderlines allowingintermediates (including transitional forms, developmental mosaics).The FAM Approach complements Cla ssical Plant M orphology (ClaMApproach), which is the traditional approach in botany. ClaMproponents (‘ClaMmers’) postulate that the structuralcategories of vascular plants are regarded as concepts withclear-cut borderlines and without intermediates. However, duringthe evolution of vascular plants, the root-shoot distinctionand the stem-leaf distinction have become blurred several timesdue to developmental changes, resulting in organs with uniquecombinations of features. This happened, for example, in thebladderworts (Utricularia, Lentibulariaceae). When focusingon the ‘leaf’, the FAM Approach is identical toArber's ‘partial-shoot theory of the leaf’ and Sinha's‘leaf shoot continuum model’. A compound leaf canrepeat the developmental pathway of the whole shoot, at leastto some degree. For example, compound leaves of Chisocheton(Meliaceae)with indeterminate apical growth and three-dimensional branchingmay be seen as developmental mosaics sharing some growth processeswith whole shoots! We focus here on the FAM Approach becausethis perspective is especially promising for developmental geneticistsstudying flowering and other vascular plants. Copyright 2001Annals of Botany Company Review, body plan, developmental mosaics, leaf development, history of botany, homeosis, homeotic genes, Lentibulariaceae, morphological evolution, process morphology, stipules, Utricularia, flowering plants     

Terbutol Affects Spindle Microtubule Organizing Centres

Light, immunofluorescence, and electron microscopy were utilizedto investigate the effects of the herbicide terbutol (2,6-di-tert-butyl-p-tolylmethylcarbamate) on onion root tips. So-called ‘star anaphases,’chromosomes drawn in at their centromeres at both poles, resultingin a starburst of chromosomes were the predominant form of mitoticabnormality noted in root tip squashes of the terbutol-treatedroots. Immunofluorescence microscopy using antitubulin serareveals a cluster of microtubules radiating from the centreof the chromosome mass at each of the poles. Nuclear envelopesapparently reform around the radially-arranged chromosome masses,resulting in extensively lobed ‘star telophase’nuclei. Branched and curved phragmoplast arrays are observed,due to interference by the lobes of the star telophase nucleus.These abnormal phragmoplasts result in incomplete and/or abnormally-orientedcell walls. Star anaphase figures are observed after 2 h ofherbicide treatment, indicating that this terbutolinduced chromosomalabnormality is a primary effect of the herbicide. Tradescantiastamen hairs were treated with terbutol and mitosis was monitoredin vivo by Nomarski differential interference microscopy; thesetreated stamen hairs produce star anaphase figures as a primaryeffect of the herbicide. This series of abnormalities has notbeen observed with any other herbicide, indicating that terbutolhas a unique mechanism of action, perhaps interacting with spindlemicrotubule organizing centres. Key words: Terbutol, Onion, root tips, star-anaphase figures     

Effects on Growth and Development of Individual Chromosomes from Slow-growing Lophopyrum elongatum Love when Incorporated into Bread Wheat (Triticum aestivum L.)

Aspects of growth and development were evaluated in the fast-developingannual Triticum aestivum L. ‘Chinese Spring’, theslow-developing perennial Lophopyrum elongatum Löve, theiramphiploid, and chromosome addition and substitution lines ofL. elongatum into ‘Chinese Spring’. Relative growthrates (RGR) of shoots of L. elongatum and the amphiploid werelower than those of ‘Chinese Spring’ (34 and 13%respectively) and main stem development was also slower. Therewas no difference in shoot RGR of any of the chromosome additionor substitution lines and that of ‘Chinese Spring’when assessed between Haun stages 2.0 and 5.0. In contrast,several aspects of plant development were observed to differin the chromosome addition and substitution lines. SubstitutingE genome chromosomes (with the exceptions of 3E and 4E) forD genome chromosomes, or adding E genome chromosomes, slowedthe rate of main stem development, at least up to Haun stage5.0. Despite these differences in the rate of main stem development,the appearance of adventitious roots commenced at approximatelyHaun stage 2.0 in all genotypes. However, the numbers of adventitiousroots and tillers at the 5.0 Haun stage differed between someof the lines when compared to ‘Chinese Spring’.Although incorporation of some L. elongatum chromosomes alteredaspects of plant development, all lines showed more similarityto bread wheat than to L. elongatum, reflecting, in part, thegreater genetic contribution made by bread wheat to these lines.Copyright 2001 Annals of Botany Company Adventitious roots, chromosome addition and substitution lines, Haun stage, Lophopyrum elongatum, relative growth rate (RGR), Triticum aestivum(wheat)     

Cytoevolution, Phylogeny and Taxonomy in Epacridaceae

Chromosome numbers in Epacridaceae were collated from variousauthors and superimposed on to recent cladograms for the family.The results strongly indicate that reduction in chromosome numberoccurs with evolutionary advancement. Thus Epacridaceae, incommon with ‘Ericaceaesens. strict .’ and ‘Vacciniaceaesens.strict. ’, has evolved from a primitive karyotype of atleastx =12 and probablyx =13. This conclusion dispels earlierpaleopolyploid models based on a primitivex =6 in the family.Other aspects of cytoevolution, such as chromosome number asa generic character especially in cytologically advanced generaof the Styphelieae, are discussed. Cytoevolution; cladistic models; primitive character states for chromosome number; dysploid falls; cytotaxonomy; Epacridaceae; Richeoideae; Epacridoideae; Epacrideae; Styphelieae; Ericaceae     

CORRECTIONS, VOLUME 29

Part 1, under the frontispiece portrait of Dr. N. B. Eales,the words ‘President 1948–1951’ should havebeen added. Page 103, line 49, for ‘Newton Collection’ read‘Norman Collection (Canon Norman)’. 185, line 37, for ‘capillaris’ read ‘capillacca’. 188, Table 1, for ‘bemoralis’. read ‘nemoralis’. 188, Table 2, for ‘Cochlicella acuta (Müll)? ventrosa(Fér.)’ read ‘Cochlicella ventrosa (Fér.)’. 191, line 24, for ‘araheo-’ read ‘archeo-’.     

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

• Background and Aims Summer dormancy in perennial grasseshas been studied inadequately, despite its potential to enhanceplant survival and persistence in Mediterranean areas. The aimof the present work was to characterize summer dormancy anddehydration tolerance in two cultivars of Dactylis glomerata(dormant ‘Kasbah’, non-dormant ‘Oasis’)and their hybrid using physiological indicators associated withthese traits. • Methods Dehydration tolerance was assessed in a glasshouseexperiment, while seasonal metabolic changes which produce putativeprotectants for drought, such as carbohydrates and dehydrinsthat might be associated with summer dormancy, were analysedin the field. • Key Results The genotypes differed in their ability tosurvive increasing soil water deficit: lethal soil water potential(_s) was –3·4 MPa for ‘Kasbah’ (althoughnon-dormant), –1·3 MPa for ‘Oasis’,and –1·6 MPa for their hybrid. In contrast, lethalwater content of apices was similar for all genotypes (approx.0·45 g H₂O g d. wt^–1), and hence the greater survivalof ‘Kasbah’ can be ascribed to better drought avoidancerather than dehydration tolerance. In autumn-sown plants, ‘Kasbah’had greatest dormancy, the hybrid was intermediate and ‘Oasis’had none. The more dormant the genotype, the lower the metabolicactivity during summer, and the earlier the activity declinedin spring. Decreased monosaccharide content was an early indicatorof dormancy induction. Accumulation of dehydrins did not correlatewith stress tolerance, but dehydrin content was a function ofthe water status of the tissues, irrespective of the soil moisture.A protein of approx. 55 kDa occurred in leaf bases of the mostdormant cultivar even in winter. • Conclusions Drought avoidance and summer dormancy arecorrelated but can be independently expressed. These traitsare heritable, allowing selection in breeding programmes.     

Identification of a chemically induced point mutation mediating herbicide tolerance in annual medics (Medicago spp.)

Background and Aims: Sulfonylurea (SU) herbicides are used extensively in cereal–livestockfarming zones as effective and cheap herbicides with usefullevels of residual activity. These residues can persist beyondthe cropping year, severely affecting legumes in general, andannual medics in particular, resulting in reduced dry matterproduction, lower seed yields and decreased nitrogen fixation.A strand medic cultivar, Medicago littoralis ‘Angel’,has been developed via chemical mutagenesis with tolerance toSU soil residues. Identifying the molecular basis of the observedtolerance was the aim of this study. Methods: Two F₂ populations were generated from crosses between ‘Angel’and varieties of intolerant M. truncatula, the male-sterilemutant tap and the cultivar ‘Caliph’. Genetic mappingwith SSR (single sequence repeat) and gene-based markers allowedidentification of the trait-defining gene. Quantitative geneexpression studies showed the activity of the respective alleles. Key Results: Segregation ratios indicated the control of SU-herbicide toleranceby a single dominant gene. SU herbicides inhibit the biosynthesisof the branched-chain amino acids by targeting the acetolactatesynthase enzyme, allowing the choice of a mapping approach usingacetolactate synthase (ALS) gene homologues as candidates. SSR-markeranalysis suggested the ALS-gene homologue on chromosome 3 inM. truncatula. The ALS-gene sequences from ‘Angel’and intolerant genotypes were sequenced. In ‘Angel’,a single point mutation from C to T translating into an aminoacid change from proline to leucine was identified. The polymorphismwas used to develop a diagnostic marker for the tolerance trait.Expression of the mutant ALS allele was confirmed by quantitativeRT-PCR and showed no differences at various seedling stagesand treatments to the corresponding wild-type allele. Conclusions: The identification of the trait-defining gene and the developmentof a diagnostic marker enable efficient introgression of thiseconomically important trait in annual medic improvement programs.     

The Nitrogen Content of Plants and the Self-thinning Rule of Plant Ecology: A Test of the Core-skin Hypothesis

The ‘core-skin’ hypothesis postulates that secondarilythickened plants behave energetically as an inert ‘core’covered by an active ‘skin’, the ‘skin’being two-imensional, the ‘core’ three-dimensional.This would explain the ‘self-thinning ‘or‘–3/2’ rule of plant ecology, that is, the tendencyfor log (dry weight per plant) and log (number of plants perunit area) to progress along a straight line relationship, withslope = – 3/2’. The hypothesis was tested as follows. Plant nitrogen contentwas used as an estimate of the mass of ‘skin’ perplant, and dry weight as an estimate of the mass of the ‘core’.As plants mature the slope of the relationship between y = log(mass of nitrogen per plant) and x = log (mass of dry matterper plant) is expected to decline from an initial value of 1.0towards a final value of 0.66. The intercept of the relationshipis expected to reflect the intrinsic content of ‘skin’per unit of ‘core’. Genotypic variation in thisparameter should cause genotypic differences in the maximumattainable yield of biomass per unit area. The expectations were investigated by fitting the function y= p+qx+r exp – x to 30 sets of data on plant nitrogencontent, plant weight and time in 18 different vegetables. Simplelinear regressions of y on x were fitted to more limited setsof data on weights and nitrogen contents of mature trees. Theexpectations were, with some minor exceptions, confirmed. Nitrogen, yield, plant competition, self-thinning     

Diurnal Phototropism in Leaves of Lavatera cretica L. under Conditions of Simulated Solar-Tracking

Diurnal laminar reorientation was followed in solar-trackingleaves of Lavatera cretica L. under simulated conditions. Asimulated ‘sun’ was moved over the lamina in a 180?arc in the vertical plane of the mid-vein, at an angular velocityof 15? h^–1 in a regime of 12-h photoperiods. In one groupof plants the petioles of the experimental leaves were arrangedto face ‘sunrise’, while in the other they werearranged to face ‘sunset’. At ‘sunrise’,the laminae in both groups, which were inclined towards theanticipated direction of ‘sunrise’, changed theirelevation towards the rising ‘sun’, resulting inprogressive reduction in the angle of incidence (AI) of lighton the laminar surface (AI= differential between laminar and‘solar’ elevation). As a result, laminar and ‘solar’elevation converged, and laminar reorientation gradually ceased,until the ‘solar’ elevation had passed the normalto the laminar surface (AI=0?). laminar reorientation was thenresumed, but its direction was reversed to follow the directionof ‘solar’ reorientation. During most of the remaining‘day’, laminar elevation (LE) trailed that of the‘sun’ by an average of 11?-14?. Laminar reorientationthen anticipated ‘sunset’ by starting to slow down60 to 90min in advance. During the 12-h dark period, the laminareoriented towards the anticipated direction of the subsequent‘sunrise’. The time-course of nocturnal reorientationwas qualitatively different in the two groups of experimentalplants. The time-course of diurnal phototropism under naturaland simulated conditions is analysed and compared and differencesand similarities between them are discussed. Key words: Diurnal phototropism, solar-tracking, vectorial excitation     

ERRATA

Effects of coupled solute and water flow in plant roots withspecial reference to Brouwer's experiment. Edwin L. Fiscus. p. 71 Abstract: Line 3 delete ‘interval’ insert‘internal’. p. 73 Materials and Methods: line 6: delete ‘diversion’ insert ‘division’ line 9 equation should read J_v=L_p P–RT(C⁰–C¹). 74 Last line of figure legend: 10^–1 should read 10^–11. 75 Line 11: delete ‘seems’ insert ‘seem’. le 1 column heading—10⁶ should read 10¹¹. 77 delete ‘...membrane in series of...’ insert ‘membranein series or...’ Delete final paragraph.     

A Seed Treatment for Eliminating Non-hybrid Plants when using Atrazine Resistance as a Genetic Marker for Hybrid Seed Production

Brassica plants, with a combination of chloroplasts encodingtriazine resistance and mitochondria encoding cytoplasmic malesterility, offer new opportunities for hybrid seed production.Such plants can be grown as a random mixture with a male parent,thereby allowing more effective pollen transfer for greaterefficiency of hybrid seed production. Harvested seed consistsof hybrid seed from the ‘female’ parent, which istriazine-resistant, and non-hybrid, triazine-sensitive seedresulting from self pollination of the ‘male’ parent. This study demonstrates that triazine-sensitive broccoli (BrassicaoleraceaL. var.italica) progeny can easily be eliminated byallowing the seed to imbibe a solution of 10 g l^-1atrazine overnightthen drying-back the seed for subsequent germination. Such atreatment prevents triazine-sensitive broccoli from developingbeyond the cotyledon stage following germination, and remainseffective for at least 3.5 years after seed treatment. The growthof triazine-resistant broccoli plants is unaffected by thisseed treatment. Atrazine; Brassica oleracea; broccoli; hybrid seed; triazine resistance; seed treatment     

Factors Affecting the Abscission of Reproductive Organs in Yellow Lupins (Lupinus luteus L.): III. ENDOGENOUS GROWTH SUBSTANCES IN VIRUS-INFECTED AND HEALTHY PLANTS AND THEIR EFFECT ON ABSCISSION

Extracts of small and mature-size lupin pods yielded four substancesaffecting the growth of wheat-coleoptile sections: one acidpromotor (A), two acid inhibitors(B and X), and one neutralinhibitor(Y). Inhibitor B was extremely active, however, coleoptile sectionsshowed no signs of toxic effects; they resumed growth at a rapidrate after rinsing them and adding ß-indolylaceticand (IAA) to the medium. 1 µg of IAA was required to counteractthe effect of ‘B’ extracted from 230 mg. Of tissue.On an equal fresh weight basis the inhibiting action of ‘B’in lupin pods was 500–1,500 times more potent than thatof ‘inhibitor ß’ in etiolated pea seedlings. Small pods of plants infected with pea-mosaic virus yielded3 times the amount of ‘A’ of healthy plants (equivalentto 1 µg. IAA 0.3 µg. IAA per 25 g. of tissue respectively),and approximately the amount of ‘B’. Mature podsof virus-infected plants again yielded more‘A’,but also 2? times more ‘B’ than pods of healthyplants. Healthy pods yielded more ‘A’ than virus-infectedpods, and there was no difference in ‘X’. A lupin abscission test was developed and the effects of proximaland distal application of -naphthyl acetic acid (NAA) are presented,and discussed with respect to results of other abscission tests. ‘A’ accelerated abscission when applied proximally,and delayed or prevented it when applied distally. ‘B’strongly accelerated abscission when applied in either way.A possible mechanism explaining the abscission-inducing effectof developing pods on later flowers is discussed in terms ofthe substances ‘A’ and ‘B’. The partlyprevented abscission observed on virus-infected plants was foundto agree well with the proposed mechanism.     

ERRATA

WARBURG, M. R., 1965. On the water economy of some Australianland snails. Proc. malac. Soc. Lond. 36, 297–305. Page 298: second line from bottom, should read ‘within± 1 µg for Themapupa’. Page 300: Fig. 2 legend, should read ‘Evaporative waterloss from Sinumelon remissum (a), Pleuroxia sp. (b) and Themapupaadelaidae (c)’. Page 300: section 4 heading, should read ‘Continuous curvesfor water loss’. Page 301: second line, for ‘Fig. 9’ read ‘Fig.3’. Page 301: Table 1, last line, for ‘0.120024’ read‘0.12024’. Present address: Israel Institute for Biological Research, Ness-Ziona,Israel.     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

Morphogenesis of 2,4-D Induced Abnormalities of the lnflorescence of Bread Wheat (Triticum aestivum, L.).

Treatment of Triticum plants with 2,4-D profoundly affects inflorescencemorphogenesis and results in the production of various abnormalities,amongst which are branched heads, whorls of spikelets. superimposedpairs of spikelets (‘banana’ twin spikelets) andpaired spikelets borne at the same level (‘yoked’spikets). Often more than one kind of abnormality is observedin a single head. Except for ‘banana’ twin spikelets,none of the induced abnormalities are duplicated by abnormalitieswhich occur spontaneously in untreated plants. Disturbance dueto treatment is only temporary and later the terminal regionof the apex recommences growth along a normal pattern of morphogenesis.     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 1. Grown as Simulated Swards During a Regrowth Period

Simulated swards of each of two selection lines of Lolium perennecv. S23 with ‘fast’ and ‘slow’ ratesof ‘mature tissue’ respiration were establishedin growth rooms at 20/15 °C day/night temperatures and studiedover four successive regrowth periods of 46, 30, 26 and 53 daysduration. The ‘slow’ line outyielded the ‘fast’,both in harvestable shoot (above a 5 cm cut) and in root andstubble. Its advantage increased over successive regrowth periodsto 23 per cent (total biomass). Gas analysis measurements onthe entire communities (including roots), during the final regrowthperiod, showed that the ‘slow’ line had a 22–34per cent lower rate of dark respiration per unit dry weight.This enabled it to maintain its greater mass of tissue for thesame cost in terms of CO₂ efflux per unit ground area. Halfthe extra dry weight produced by the ‘slow’ line,relative to the ‘fast’, could be attributed to itsmore economic use of carbon. The rest could be traced to a 25per cent greater tiller number which enabled the ‘slow’line to expand leaf area faster (though not at a greater rateper tiller), intercept more light and fix more carbon, earlyin the regrowth period. Lolium perenne L., ryegrass, respiration, maintenance respiration, tiller production, simulated swards, canopy photosynthesis, carbon economy