Investigation of Bidirectional Movement of Tracers in Sieve Tubes of Salix Viminalis L.

Sieve-tube sap was collected as honeydew from the aphid Tuberolachnussalignus (Gmelin) feeding on a young shoot or a mature stemof willow (Salix viminalis L.). Two radioactive tracers (either³H-glucose and ¹⁴C-sucrose, or ¹⁴CO₂, Na₂ ¹⁴CO₃, and ³²P-orthophosphate)were applied to leaves or to bark abrasions at each end of thestem. In some experiments the tracers were applied after thestart of honeydew production, whilst in others the tracers wereapplied before the aphids were sited. In most cases aphids feeding between the tracer applicationpoints produced doubly-labelled honeydew during a 24–48-hperiod from tracer application. In some instances the firstdrops of honeydew contained one tracer, followed several hourslater by the other tracer, whilst some aphids produced doubly-labelledhoneydew from the first drop. Singly-labelled or inactive honeydewwas found in only a few cases. It was demonstrated that when ³H-glucose and ¹⁴C-sucrose wereapplied at opposite ends of a stem that the tracers moved inopposite directions in the form of sucrose. The data suggest that a simultaneous bidirectional movementof two tracers may occur in the same sieve tube. However, thepossibility that the doubly-labelled honeydew could be producedby lateral movement from one sieve tube carrying one tracerto an adjacent punctured sieve tube carrying the other tracercannot be discounted.     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

Sclerophylly and Plant Water Relations in Three Mediterranean Quercus Species

The possible role in drought resistance played by sclerophyllywas studied in the Mediterranean oaks Quercus ilex, Q. suberand Q. pubescens. Studies were conducted on leaves at 30, 50and 80% of their final surface area, as well as on mature leavesof the current year's growth in June and September and on 1-year-oldleaves. Leaves of different ages of the three species showed quite differentdegrees of sclerophylly (DS). Q. ilex leaves reached the definitiveDS of 1.75 g dm^–2 during leaf expansion; Q. pubescensleaves hardened at the end of their expansion, with a finalDS of 0.93 g dm^–2; Q. suber showed the lowest DS of 0.76g dm^–2. Leaf conductance to water vapour (g₁) of 1-year-old leaves ofQ. ilex, measured in the field, showed a duration of the g₁peak values about twice that of the other two species. The minimumleaf relative water content (RWC), however, was near the samein the three species, indicating that water loss was recoveredpartly by Q. ilex leaves. This was apparently due to the higherbulk modulus of elasticity (     

Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare

Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m^–3‘control’ and 100 mol m^–3) in the presenceof 6.5 mol m^–3 K ⁺. Between 16 and 31 d after germination,before stem elongation started, xylem sap was collected by useof a pressure chamber. Collections were made at three differentsites on leaves 1 and 3: at the base of the sheath, at the baseof the blade, i.e. above the ligule, and at the tip of the blade.Phloem sap was collected from leaf 3 at similar sites throughaphid stylets. The concentrations of K ⁺, Na⁺, Mg2⁺ and Ca²⁺were measured. Ion concentrations in xylem sap collected at the base of leaves1 and 3 were identical, indicating there was no preferentialdelivery of specific ions to older leaves. All ion concentrationsin the xylem decreased from the base of the leaf towards thetip; these gradients were remarkably steep for young leaves,indicating high rates of ion uptake from the xylem. The gradientsdecreased with leaf age, but did not disappear completely. In phloem sap, concentrations of K⁺ and total osmolality declinedslightly from the tip to the base of leaves of both controland salt-treated plants. By contrast, Na⁺ concentrations inphloem sap collected from salt-treated plants decreased drasticallyfrom 21 mol m^–3 at the tip to 7.5 mol m^–3 at thebase. Data of K/Na ratios in xylem and phloem sap were used to constructan empirical model of Na⁺ and K⁺ flows within xylem and phloemduring the life cycle of a leaf, indicating recirculation ofNa⁺ within the leaf. Key words: Hordeum vulgare, xylem transport, phloem transport, NaCl-stress     

The Effect of Current Photosynthesis on the Origin of Translocates in Old Tomato Leaves

The rate of carbon transport from an old tomato leaf (54 days),grown at 80 W m^–2, was measured under light flux densitiesbetween 7 and 90 W m^–2. Under low light, the rate of carbontransport over a 6 h period was about 1 mg C dm^–2 h^–1,well in excess of the concurrent photosynthetic rate. The lossfrom these leaves of ¹⁴C-leaf assimilate which was fixed beforethe experimental period amounted to 62 per cent of the totalinitial uptake and was higher than that from leaves with higherconcurrent photosynthetic rates. The higher loss of ¹⁴C fromleaves with low photosynthetic rates was due to a greater contributionof ¹⁴C from the starch and residue fractions. The rate of transportappeared to be determined by the concentration of the labilesucrose, not the total sucrose concentration. In comparisonwith young fully-expanded tomato leaves (Ho, 1976) the sizeof the labile sucrose pool appeared to decrease with age. Thephotosynthesistranslocation coefficient was low (k₁k₂=0•21)for an old tomato leaf. Based on these results a scheme of carbonpartitioning in relation to translocation is proposed. Criteriafor assessing the efficiency of translocation in leaves arediscussed.     

Photosynthesis of White Clover Leaves as Influenced by Canopy Position, Leaf Age, and Temperature

Microswards of white clover (Trifolium repens L.) were grownin controlled environments at 10/7, 18/13 and 26/21 °C day/nighttemperatures. The vertical distribution of leaves of differentages and their rates of ¹⁴CO₂-uptake in situ were studied. Extending petioles carried the laminae of young leaves throughthe existing foliage. A final position was reached within 1/4to 1/3 of the time between unfolding and death. Newly unfoldedleaves had higher rates of ¹⁴CO₂-uptake per leaf area than olderones at the same height in the canopy. At higher temperatures,the decrease with age was faster. However, the light-photosynthesisresponse of leaves which were removed from different heightsin the canopy varied much less with leaf age than did the ratesof ¹⁴CO₂-uptake in situ. The comparison of the rates of ¹⁴CO₂-uptake in situ with thelight-photosynthesis response curves suggests that young leavesreceive more light than older ones at the same height in thecanopy. This would imply that young white clover leaves havethe ability to reach canopy positions having a favourable lightenvironment. This ability may improve the chances of survivalof white clover in competition with other species. Trifolium repens L., white clover, photosynthesis, canopy, leaf age, ¹⁴CO₂-uptake, ecotypes, temperature     

Photosynthetic Units and Carbon Assimilation in Leaves of Grain Sorghum under Different Light Intensities

The Cyt f and P700 contents in leaves of three Sorghum, varietieswere measured, in relation to their carbon assimilation, underdifferent light intensities during growth. At the maximum irradiationused (1,800 µE m^–2 s^–1) the ratio of P700to Cyt f was close to unity, whereas under low irradiation (450µE m^–2 s^–1) the ratio of P700 to Cyt f rangedfrom two to three. A strikingly positive correlation existedbetween the P700 contents of the leaves and their rates of carbondioxide fixation, dry matter production and Cyt f contents,only when the plants were grown under high light intensities.The P700 content of the leaves in plants grown under low irradiationwas unrelated to the contents of Cyt f. Thus, at a high lightintensity there is a close relationship between the Cyt f andP700 levels, but at low intensities the amounts of electroncarriers and the reaction centre are independent. (Received March 7, 1983; Accepted August 24, 1983)     

Pattern and Control of Distribution of 14C-assimilates in Reproductive Plants of Lolium multiflorum Lam. var. Westerwoldicum

The distribution of ¹⁴C-assimilates was examined in reproductiveplants of Lolium multiflorum Lam. var. Westerwoldicum (cv. Tama)from which all emerged tillers had been removed, leaving themain tiller with two expanding leaves, one of them the flagleaf, and two expanded leaves. Export of ¹⁴C from the lowerexpanded leaf was mainly to the tiller in its axil, the steminternode below its node and the roots, whereas the upper expandedleaf supplied predominantly the expanding leaves, the ear, steminternodes, roots and the tiller bud in the axil of the lowerleaf. Defoliation and root-pruning showed that expanding leaveswere able to compete successfully for assimilates, probablythrough the production of substances capable of mobilizing supply.Local application of 1-naphthaleneacetic acid (NAA), gibberellicacid (GA₃) and 6-benzylaminopurine (BAP) to small tiller budsshowed that GA³ and BAP promoted bud growth and ¹⁴C accumulation,but that addition of NAA reduced these effects.     

Simultaneous CO2- and 16O2/18O2-gas exchange and fluorescence measurements indicate differences in light energy dissipation between the wild type and the phytochrome-deficient aurea mutant of tomato during water stress

The CO₂-, H₂O- and ¹⁶O₂/¹⁸O₂ isotopic-gas exchange and the fluorescencequenching by attached leaves of the wild-type and of the phytochrome-deficienttomato aurea mutant was compared in relation to water stressand the photon fluence rate. The chlorophyll content of aurealeaves was reduced and the ultra-structure of the chloroplastswas altered. Nevertheless, the maximum rate of net CO₂ uptakein air by the yellow-green leaves of the aurea mutant was similarto that by the dark-green wild-type leaves. However, less O₂was produced by the leaves of the aurea mutant than by leavesof the wild-type. This result indicates a reduced rate of photosyntheticelectron flux in aurea mutant leaves. No difference in bothphotochemical and non-photochemical fluorescence quenching wasfound between wild-type and aurea mutant leaves. Water stresswas correlated with a reversible decrease in the rates of bothnet CO₂ uptake and transpiration by wild-type and aurea mutantleaves. The rate of gross ¹⁶O₂ evolution by both wild-type andaurea mutant leaves was fairly unaffected by water stress. Thisresult shows that in both wild-type and aurea leaves, the photochemicalprocesses are highly resistant to water stress. The rate ofgross ¹⁸O₂ uptake by wild-type leaves increased during waterstress when the photon fluence rate was high. Under the sameconditions, the rate of gross ¹⁸O₂ uptake by ^aurea mutant leavesremained unchanged. The physiological significane of this differencewith respect to the (presumed) importance of oxygen reductionin photoprotection is discussed. Key words: Water stress, gas exchange, fluorescence quenching, Lycopersicon esculentum, mutant (tomato, aurea), energy dissipation     

Patterns of Assimilate Distribution and Source--sink Relationships in the Young Reproductive Tomato Plant (Lycopersicon esculentum Mill.)

Patterns of distribution of ¹⁴C were determined in 47-day-oldtomato plants (Lycopersicon esculentum Mill.) 24 h after theapplication of [¹⁴C]sucrose to individual source leaves fromleaves 1–10 (leaf 1 being the first leaf produced abovethe cotyledons). The first inflorescence of these plants wasbetween the ‘buds visible’ and the ‘firstanthesis’ stages of development. The predominant sink organs in these plants were the root system,the stem, the developing first inflorescence and the shoot ‘apex’(all tissues above node 10). The contribution made by individualsource leaves to the assimilate reaching these organs dependedupon the vertical position of the leaf on the main-stem axisand upon its position with respect to the phyllotactic arrangementof the leaves about this axis. The root system received assimilateprincipally from leaf 5 and higher leaves, and the stem apexfrom the four lowest leaves. The developing first inflorescencereceived assimilates mainly from leaves in the two orthostichiesadjacent to the radial position of the inflorescence on thevertical axis of the plant; these included leaves which weremajor contributors of ¹⁴C to the root system (leaves 6 and 8)and to the shoot apex (leaves 1 and 3). This pattern of distributionof assimilate may explain why root-restriction treatments andremoval of young leaves at the shoot apex can reduce the extentof flower bud abortion in the first inflorescence under conditionsof reduced photoassimilate availability. Lycopersicon esculentum Mill, tomato, assimilate distribution, source-sink relationships     

Light Distribution and Photosynthesis in Field Crops

In a new model of light distribution in field crops a parameters is the fraction of light passing through unit leaf layer withoutinterception. Radiation profiles measured with solarimetersand photocells give values of s from 0.7 for grasses to 0.4for species with prostrate leaves. Knowing s, leaf transmissionT and leaf-area index L the light distribution in a field cropmay be described by a binomial expansion of the form {s+(I-s)T)^L.To calculate crop photosynthesis at given light intensity thisexpansion is combined with two parameters describing the shapeof the light-response curve of single leaves. Finally, the assumptionthat solar radiation varies sinusoidally allows daily totalphotosynthesis to be estimated from daylength and insolation. The theory predicts about the same potential photosynthesisin a cloudy temperte climate with long days as in a more sunnyequatorial climate with short days. When L < 3 photosynthesisincreases as s decreases, i.e. as leaves become more prostrate;but when L > 5, photosynthesis increases as s increases,i. e. as leaves become more erect. Assuming that respirationis proportional to leaf area, estimated dry-matter productionagrees well with field measurements on sugar-beet, sugar-cane,kale, and subterranean clover. Estimates of maximum gross photosynthesis(for sugar-cane and maize) range from 60 to 9 g m^–2 day^–1depending on insolation.     

Leaf Development in Lolium temulentum: Photosynthesis and Photosynthetic Proteins in Leaves Senescing under Different Irradiances

Changes in carbon fixation rate and the levels of photosyntheticproteins were measured in fourth leaves of Lolium temulentumgrown until full expansion at 360 µmol quanta m^–2s^–1 and subsequently at the same irradiance or shadedto 90 µmol m^–2 s^–1. Ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco), light-harvesting chlorophylla/b protein of photosystem II (LHCII), 65 kDa protein of photosystemI (PSI), cytochrome f (Cytf) and coupling factor 1 (CF₁) declinedsteadily in amount throughout senescence in unshaded leaves.In shaded leaves, however, the decrease in LHCII and the 65kDa protein was delayed until later in senescence whereas theamount of Cyt f protein decreased rapidly following transferto shade and was lower than that of unshaded leaves at the earlyand middle stages of senescence. Decreases in the Rubisco andCF₁ of shaded leaves occurred at slightly reduced rates comparedwith unshaded leaves. These results indicate that chloroplastproteins in fully-expanded leaves are controlled individually,in a direction appropriate to acclimate photosynthesis to agiven irradiance during senescence. (Received August 20, 1992; Accepted January 5, 1993)     

The Pathway of Assimilate Flow from Source to Sink in Urtica dioica L., Studied with14C under Ambient Atmospheric Conditions

The contribution of individual vascular bundles of the stemto the flow of assimilates from a selected source leaf to thesink regions was investigated inUrtica dioica L., a plant witha decussate leaf arrangement. Two homologous sets of eight vascularstrands were recognized, arranged in mirror symmetry in thestem internodes. In each set, three of the bundles were identifiedas traces of one leaf merging into the vascular system of thestem one node below the origin of the leaf. The main bundleof a stem-half bifurcates at each end of the internode intotwo subdominant bundles, which combine in the next but one nodeto form the dominant bundle again. Each set of vascular strandsalso contains two minor bundles which pass more or less withoutinterruption through the whole stem. The uppermost mature source leaf (leaf number 5 as counted fromthe tip) was exposed to¹⁴CO₂in a closed gas circuit. The concentrationof the carbon-labelled CO₂was maintained at the ambient CO₂levelto maintain the natural source strength of the leaf. By theend of the usual nocturnal dark phase, carbon from the sourceleaf had been imported predominantly by sink leaves of the sameorthostichy. Lesser, but significant amounts of radiocarbonwere also incorporated into the sink leaves of the adjacenttwo orthostichies via the marginal leaf traces. In spite ofthe junction of the vascular strands in the nodes and an interfascicularconnection of the stem bundles, randomization of the photosynthatesfrom individual leaves was minimal in the vascular system ofthe stem in the upward direction, and also low in the flux tothe roots. Substantial amounts of radioactivity were also foundin the lately-formed xylem elements of the vascular strandsand their interfascicular connections, indicating active secondarygrowth. Assimilate distribution; source–sink connections; Urtica dioica ; vascular architecture     

An Unusual Pattern of 65Zn Distribution in the Leaves of Some Grasses

Autoradiographs of leaves of ryegrass plants (Lolium sp.) takingup radioactive zinc (⁶⁵Zn) from soil showed an unusual patternof label distribution. Tracer accumulated in a regular seriesof pulses along leaf veins. Pulses in adjacent veins occurredin juxtaposition forming the pattern of a band across the leaf. The possibilities of artifacts resulting from plant-culturetechnique or methods of preparing leaves for autoradiographywere eliminated. The band effect in leaves of Loliumand other grass species occurredwith ⁶⁵Zn but not ¹⁹Fe or ⁵⁴Mn. Leaves of Hordeum vulgare, Zeamays, Bromus rigidus, and two non-gramineous species did notshow the band phenomenon with ⁶⁵Zn. There was a close relationshipbetween the frequency of bands and the rate of growth of a leaf.The band pattern was shown to be responsive to changes in daylengthand temperature during growth. Possible origins of the band phenomenon are discussed.     

Glandular Trichomes in Satureja thymbra Leaves

The leaves of the aromatic plant Satureja thymbra have numerousglandular trichomes of two morphologically distinct types glandularhairs and glandular scales Investigations of the anatomy ofthese glandular trichomes with serial thick sections revealedthat the glandular hairs consist of three cells a foot, stalkand head cell Glandular scales also have a unicellular footand stalk Their heads, however, are composed of 12 cells Fourof these cells are small, occupying the central region of thehead, whereas the remainder are large and peripherally arrangedMorphometric analysis showed that, in leaf surface view, glandularscales are about 17-fold larger than glandular hairs In addition,glandular scales were found to occupy 5 7 % of the entire leafsurface area In each glandular scale the total amount of essentialoil, contained within both the subcuticular space and the interiorof the secretory cells, was calculated to be 2 51 x 10^–4mm³ The volume of the essential oil produced by all glandularscales on a single mature leaf was correspondingly determinedto be 0.059 mm³ Finally, the theoretical essential oil yieldof 100 g dry leaves of S thymbra was estimated to be 3 54 %(secretory activity of glandular scales only) Satureja thymbra, glandular trichomes, morphology, morphometry     

The Influence of Plant-Growth Factors on the Initiation and Growth of Crown-Gall Tumours on Primary Pinto Bean Leaves

The number of tumours developing on primary pinto bean leaves(Phaseolus vulgaris L. variety Pinto) inoculated with Agrobacteriumtumefaciens (Smith and Town.) Conn, strain B6, was increasedby as much as 100 per cent through the addition of several plant-growthfactors and antagonists of some of these factors to the freshlyinoculated leaves. Naphthylacetic acid, gibberellic acid, (2-chloroethyl)trimethylammonium chloride, and adenine gave a biphasic responsewith optimal promotions of tumour initiation at 10^-5 to 10^-4mg/ml. Tri-iodobenzoic acid and 4-chlorophenoxyisobutyric acidwere most active at 10^-1 mg/ml. Mean tumour diameter showeda direct correlation with tumour number in these experiments.The results show tumour initiation to be sensitive to growthfactor changes, possibly through a heightened traumatic responseof the wounded leaves. The growth of the tumours was unaffectedby these additions except as they altered tumour number andthis secondarily affected tumour growth.     

Reactions of birch leaves to changes in light during early ontogeny: comparison between in vivo and in vitro techniques to measure carbon uptake

Trends in several photosynthetic parameters and their responseto changed growth light were followed for 15 d in leaves ofyoung birch saplings using a rapid-response gas exchange measuringequipment. These in vivo measurements were compared to biochemicalassays that were made from the same leaves after the gas exchangestudies. The measurements were made on leaves that were selectedprior to the study and were at that time of similar age. Forthe first 7 d the photosynthetic parameters were followed fromthe growth conditions of moderate light (200 µmol m^–2s^–1; referred to as controls later in the text). On day7 some of the saplings were transferred to grow either underhigh (450 µmol m^–2 s^–1; referred to as highlight plants) or low (75 µmol m^–2 s^–1; referredto as low light plants) light and the capability of the preselectedleaves for acclimation was followed for 6 d. For comparison,at the end of the experiment the measurements were made on bothcontrols and on young leaves that had developed under high andlow light. Generally the in vivo measured rate of CO₂ uptake (gross photosynthesis)both at 310 ppm CO₂ and 2000 ppm CO₂ corresponded very wellto the biochemically determined CO₂ fixation capacity in vitroafter rapid extraction (measured as the initial and total activityof Rubisco, respectively). However, if the flux of CO₂ intothe chloroplasts was limited by the closure of the stomata,as was the case of the high light plants, then the in vitromeasured Rubisco activity was greater than the in vivo measuredCO₂ uptake. V_max, calculated from the mesophyll conductanceat 1% O₂, exceeded the initial activity of Rubisco (assayedat saturating RuBP and CO₂) constantly by 60%. The catalyticactivity of Rubisco in birch leaves was overall very low, evenwhen calculated from the total activity of Rubisco (K_cat 0.63–1.18 s^–1), when compared to herbaceous C₃ species. Signs of light acclimation were not observed in most of thephotosynthetic parameters and in chloroplast structure whenmature birch leaves were subjected to changes in growth lightfor 6 d. However, the change of the growth light either to highor low light caused day-to-day fluctuations in most of the measuredphotosynthetic parameters and in the case of the high lightplants signs of photoinhibition and photodestruction were alsoobserved (decrease in the amount of chlorophyll and increasein chlorophyll a/b ratio). As a result of these fluctuationsthese plants achieved a new and lower steady-state conditionbetween the light and dark reactions, as judged from the molarratio of RuBP to Rubisco binding site. Key words: Acclimation, photosynthesis, light, Rubisco, birch     

Age Dependent Damage and Glutathione Metabolism in Ozone Fumigated Barley: A Leaf Section Approach

First, second, and third leaves of barley (Hordeum vulgare L.cv. Atem) seedlings fumigated with 200 nl 1^–1 ozone for5 d were divided into equal length quarter sections before analysisof glutathione metabolism. Since the first leaf is the oldestand the third leaf is the youngest and since monocotyledonousleaves grow from the base, sections were of a widely differingage. Lipid peroxidation rose moderately in all sections in all leaves.However, severe damage, detected visibly as chlorosis and analyticallyas loss of soluble protein, occurred only in the oldest tissue. The specific activity of glutathione reductase was slightlyelevated in old and middle-aged tissue whilst the specific activityof glutathione-S-transferase rose markedly in old, middle-aged,and young tissue following fumigation. This may reflect theimportance of glutathione-S-transferase in the protection ofplant cells from oxidative stress products formed in membranes. Fumigation with ozone also caused a loss of total glutathionein the tip sections of all leaves. Explanations for these results, including age dependent proteinloss, are discussed. Key words: Barley, ozone, glutathione, developmental age, glutathione-S-transferase     

Age-related Changes in Stomatal Response to Cytokinins and Abscisic Acid

Kinetin and zeatin(100 mmol m^–3)reversald the ABA-mediated(100mmol ^m-2)closure of stomata of young maize leaves but did notaffect stomatal apertures of these leaves when applied alone.As leaves aged, kinetin or zeatin alone promoted increased stomatalapertures, while abscisic acid (ABA) applied alone had a reducedeffect on stomata. Even with older leaves, cytokinins reversadthe effect of ABA on stomata. Maize, stomata, abscisic acid, kineusc, zeatin, Zea mays     

Vascular and General Anatomy of the Rootstocks of Three Stemless Viola Species

The primary vascular system of the rootstock of Viola rotundifolia,V. odorata and V. cucullata consists of an open system of threesympodia, corresponding to three orthostichies (parastichies)of leaves in the 1 /3 phyllotaxy. Between the major, collateralbundles there are vascular strands consisting of only primaryphloem. The vascular supply to axillary buds developing in thefirst season of growth is the same in flowering and vegetativebuds and there is a homology between the bracts on the pedunclesof axillary flowers and the prophylls of the axillary vegetativebranches. The overwintering portions of the rootstocks are somewhatwoody. The uneven development of secondary xylem correspondsto the locations of the sympodia. Secondary xylem closes a leafgap of a median trace only slowly, but any gap in the phloicsystem is closed quickly by secondary growth. Viola rotundifolia, V. odorata, V. cucullata, rootstock, vascular anatomy