The Site of Water Evaporation from Sub-stomatal Cavities, Liquid Path Resistances and Hydroactive Stomatal Closure

A computer was used to carry out numerical iterations of thediffusion pattern of water vapour in models of sub-stomatalcavities. The cavities were simple hemispheres and cylindershaving uniformly wet interior surfaces. In the simulations waterwas allowed to diffuse from the vapour saturated wet surfacesto a single hole which simulated a stoma. After many simulationswe concluded that about of all water evaporation occurs inthe region corresponding to the guard cells. We think that alarge degree of peri-stomatal evaporation will occur in realsub-stomatal cavities. We have reviewed some of the literature on liquid pathways andresistances in leaves and conclude that the resistance to waterflow from veins to the nearest guard cell is large enough tocause substantial localized dehydration of the guard cell resultingin hydroactive stomatal closure. We also suggest that: (1) theuse of apoplastic dyes to trace the pathway of water movementin leaves cannot give the correct answer; (2) the reported conductivityof epidermal tissue to water is impossibly high; and (3) previousgravimetric measurements of peristomatal evaporation on largescale models of sub-stomatal cavities were subject to waterloss by convection and therefore underestimated the degree ofperistomatal evaporation. We also argue that all wet interfaces take up CO₂ more or lessuniformly even though evaporation of water is mostly peristomatal.The ramified internal structure of leaves therefore allows CO₂uptake with relatively little water loss. stomata, sub-stomatal cavities, transpiration, peristomatal evaporation     

The Hydraulic Pathways in Nicotiana glauca (Grah.) and Tradescantia virginiana (L.) Leaves, and Water Potentials in Leaf Epidermes

The hydraulic conductances of leaves of a species which exhibitsstomatal responses to humidity (Nicotiana glauca) are significantlylower than the conductances in a species which does not exhibitsuch responses (Tradescantia virginiana). This difference couldat least partly account for their difference in stomatal responseto humidity. In both species, the hydraulic conductance betweenthe leaf bulk and its epidermis is much lower than the conductancein any other part of the pathway. The apparently conflictingresults, reported in recent literature, on the hydraulic conductancesand water pathways in leaves are reinterpreted, and shown tobe due to misinterpretation of results. The recently publishedcriticisms of a technique used to measure hydraulic conductivityare commented on and refuted. An examination of the factors that influence the water potentialat the sites of evaporation from the inner walls of the epidermisnear stomatal pores showed that the water potential at thesesites is lower than the bulk epidermal water potential. Thewater potential at these sites changes in a complex way as stomatalaperture changes. As it is reduced the ratio of: ‘waterpotential at sites of evaporation on the inner walls of theepidermis near stomatal pores/bulk leaf water potential‘increases. The positive feedback effect of this phenomenon,which tends to keep stomatal water potential constant as thestomata close and therefore enhances closure, and two other‘passive’ positive feedback effects on the waterpotential at sites of evaporation near stomata that have beenreported in the literature are briefly discussed. Nicotiana glauca (Grah.), Tradescantia virginiana (L.), sub-stomatal cavities, peristomatal evaporation, stomata, humidity response, leaf hydraulic conductance, water potential     

Impact of soil vertical water movement on the energy balance of different land surfaces

The soil heat flux determination method proposed by Gao (Boundary-Layer Meteorol 114:165–178, 2005) is discussed for (1) dry surfaces, (2) bare soil or sparse short-grass lands, and (3) dense-grass surfaces or forest. Our analysis shows that, when neglecting the contribution of soil vertical water movement to soil heat flux, the energy components measured independently will (1) still achieve balance over dry surfaces, and (2) be significantly in imbalance over bare soil or sparse short-grass lands. The mean of bare ground evaporation modeled by SiB2 is 1.58 × 10⁻⁵ m³ s⁻¹ m⁻², and the mean of soil water flux obtained by the method of Gao is 1.22 × 10⁻⁵ m³ s⁻¹ m⁻² for the Naqu site in the summer of 1998. Comparison of the bare ground evaporation with the mean of soil water flux shows a difference, the causes of which are investigated. Physically, the bare ground evaporation is equal to the sum of soil water flux and water content change in the soil surface layer. Because the bare ground evaporation is very limited for the dense-grass surfaces or forest, our analysis implies that the energy imbalance encountered over the dense-grass or forest is not caused by the fact that previous researchers neglected soil water movements in their energy budget analyses.     

The Stability of the Growth Pattern of Young Apple-trees under Four Levels of Illumination: With four Figures in the Text

As part of a programme on the characterization of the growthpattern of the apple-tree, uniform I-year-old plants carryingtwo new shoots were grown for a season under 100, 78, 41, or24 per cent, natural light. Weights of leaf, new stem, old stem,and root were determined by sampling on 6 occasions. The dryweightincrements over the whole season ranged from 17 to 151 g. ofwhich, in full light, 22 per cent, was leaf and 22 per cent,was root; in deep shade, 32 percent, was leaf and 8 per cent,was root; and under all conditions 56–60 per cent, wasstem. These percentages were the cumulative result of currentrates of growth of leaf, stem, and root over the whole growingperiod. The rates were not constant relative to one another,but the much greater quantity of growth made over the period100–200 days from bud-break swamped earlier differences.All treatments showed the same basic pattern of growth withminor differences increasing with the intensity of shading.These differences are discussed in relation to utilization ofreserves and the demands of the various regions of the plant.The response to shading was analysed into the effects of reducedlight interception, increased leaf dispersion, increased leafproportion, reduced length of growing season, and lighter leafweight at the beginning of the 20-leaf stage. The result ofthese factors was a doubling of the growth expected in the absenceof response. It was concluded that the pattern of growth isstable, and the conditions for the perpetuation of such stablepatterns as a necessary qualification for tree growth are brieflydiscussed.     

A study of the transpiration surfaces of Avena sterilis L. var. Algerian leaves using monosilicic acid as a tracer for water movement

Summary The sites and pathways of transpiration from leaves of Avena sterilis L. var. Algerian were studied using the accumulation of monosilicic acid as a tracer for water movement. Seedlings of Algerian oats were grown under silicon free conditions and fed monosilicic acid, in a normal nutrient solution, via the roots. The silicon component of monosilicic acid was located in freeze substituted tissue by means of x-ray microprobe analysis. Methods of tissue fixation preventing post treatment movement of tracer were developed and it was determined that monosilicic acid is a suitable tracer for water.Sites of water loss were marked by accumulation of silicon. Internal evaporating surfaces having a high intensity of water loss were demonstrated. Evaporation from epidermal surfaces was most intense over the guard and subsidiary cells with very little evaporation from the cuticular surfaces of normal epidermal cells. Moderately high evaporation occurred from epidermal fibre cells located above the veins. Evaporation from all exposed walls of guard cells including the wall adjacent to the pore was intense. Smaller amounts of tracer were located in the unexposed anticlinal walls of epidermal cells as well as within the unexposed walls of mesophyll cells. The results are interpreted as demonstrating the extent of internal transpiration surfaces and that cuticular epidermal transpiration is low. Strong support is given to the existence of peristomatal transpiration. Internal pathways of water movement are defined and the occurrence of these is discussed in relation to cuticular transpiration and lateral water movement in the epidermis.     

Foliar anatomy and micromorphology of eleven species of Eugenia L. (Myrtaceae)

The anatomy and micromorphology of eleven species of Eugenia found in the 'restinga' of Marica, Rio de Janeiro, Brazil, were studied and compared. The characteristics found to be of most use in distinguishing the species are: presence and types of trichomes persistent in the adult material, form and arrangement of overlying cells (epidermal cells over secretory cavities), pattern of anticlinal walls of epidermal cells (primary sculpturing), occurrence of epicuticular striae and folds (secondary sculpturing) and presence of peristomatal folds. An analytical key based on these characteristics is presented for the Eugenia species studied.     

Cyclic Changes in Transpiration of Sunflower Leaves in a Steady Environment

Concurrent cyclic changes of leaf temperature, transpirationrate, and stomatal aperture were found to occur in plants ofsunflower (Helianthus annuus L.) exposed to a steady aerialenvironment and with their roots in water. These cyclic changeswere less regular with plants in drying soils and did not occurat all with plants in soils with a water potential less than–120 J kg^–1. A sequence of possible events whichlead to the repeated cycling is suggested; these involve relativechanges in the turgor of epidermal and guard cells. The possibilitythat repeated cycling may be caused by a changing concentrationof carbon dioxide in the sub-stomatal cavities is also discussed.The irregularity and eventual cessation of these cyclic changesare considered to be due to the reduction in turgor of the epidermaland guard cells as the availability of water to these cellsis reduced.     

Phloem and Xylem Transport in the Supply of Minerals to a Developing Legume (Lupinus albus L.) Fruit

The economy of carbon, nitrogen, water and mineral elementsin fruits of Lupinus albus L. was studied by measuring accumulationof these quantities in the developing fruit and estimating itstranspirational losses and CO₂ exchanges. Combining this informationwith data on levels of mineral elements in the xylem sap andphloem sap supplying the fruit, it was possible to test whethertransport based on mass inflow through xylem and phloem wouldaccount for the observed intake of elements. A model of transportbased on water and carbon intake suggested that vascular intakeduring the fruit's life matched the recorded increment for mineralsto within ± 15 per cent for N, Na, Zn, Fe and Cu, andto within ± 23 per cent for P, K and S. However, estimatedvascular intake of Ca, Mg and Mn accounted for less than one–thirdof the recorded intake by the fruit, inadequacy of vascularintake being especially great early in growth. Transport inphloem accounted for more than 80 per cent of the fruit's vascularintake of C, N and S, and 70–80 per cent of its P, K,Mg and Zn. Xylem contributed 68 per cent of the vascular inputof Ca, 59 per cent of the Na, and 34–38 per cent of theFe, Mn and Cu. Enclosure and darkening of fruits reduced levelsof Ca and Fe but increased levels of N, P, K and Zn in fruitdry matter relative to unenclosed, illuminated fruits. Resultswere related to previous observations on fruit functioning. Lupinus albus, legume fruit, mineral supply, phloem, xylem     

Scanning Electron Microscopy of Pseudomonas syringae pv, morsprunorum on Sweet Cherry Leaves

Scanning electron microscopy indicated that sub-stomatal cavities on sweet cherry leaves are “protected sites” which shelter resident populations of Pseudomonas syringae pv. morsprunorum. Bacteria entered the stomata, multiplied in the cavities and emerged in a mass 6 days after inoculation. There were no visible symptoms, suggesting that the pathogen colonized the host in “sub-clinical” numbers to generate populations which were then released onto the leaf surface under suitable conditions.     

An Examination of the Factors affecting Variability in the Growth of the Mesocotyl and Coleoptile of Etiolated Avena Seedlings

Experiments were carried out on the effect of rate of air-flowand of humidity on the growth of Avena seedlings. The experimentalmethods used are described in some detail. The effect of air-flow on mesocoryl growth was considerablewhen unsaturated air was used, but with saturated air growthwas independent of air-flow. The effect must therefore be dueto variation in transpiration rate. A 10 per cent, variationin relative humidity, at a constant rate of flow, caused a 30per cent, variation in mesocotyl length. The coleoptiles showedless pronounced effects, but even in saturated air variabilitywas not eliminated. Under the conditions used a difference of 2·3 mm. inmesocotyl length (per 50 plants), i.e. 8 per cent., was significantat P = 0·05; for the coleoptiles a difference of 1 mm.(8 per cent.) was significant at this level.     

The Effect of Temperature and Moisture Content on the Longevity of Seed of Ulmus carpinifolia and Terminalia brassii

Seeds of the Smooth-leafed Elm (Uimus carpinifolia) and of thetropical forest tree Terb (Terminalia brassii) were stored hermeticallyand sampled at intervals for periods of up to two years. Bothspecies possess ‘orthodox’ seed (increasing longevityis observed as either moisture content or temperature are reduced)within the temperature ranges from — 13 to 52°C (Elm)and from —4 to 42°C (Terb) and within the moisturecontent ranges from 3 to 19 per cent (Elm) and from 5 to 14per cent (Terb) on a fresh weight basis. Elm seed stored at—75°C showed the expected relationship between longevityand moisture content, but did not differ significantly in longevityfrom seed kept at — 13°C when moisture contents wereheld constant. Probit analysis of the relationship between germinationpercentage and time was performed for each storage environment,yielding a slope from which the standard deviation of the distributionof seed deaths over time () was calculated. Standard deviationvalues were used in turn to determine the values of constantsin a viability equation which had previously been applied toseed of barley, chickpea, cowpea and soybean. The equation,which gave a good fit to the results obtained, can be used topredict viability for seed in storage over a wide range of environmentalconditions. Some limitations to the applicability of the viability equationwere defined. At 22 per cent and higher moisture contents Elmseed survived longer than predicted. Furthermore, all Elm andTerb seed was killed quickly on placing in —75°C at22 and 20 per cent moisture content respectively, but high viabilitywas retained for several days at 19 and 17 per cent respectively.Practical implications of the results are discussed. Uimus carpinifolia Gleditsch, Smooth-leafed Elm, Terminalia brassii Exell, Terb, seed longevity, seed storage, moisture content, temperature     

Germination of Talinum triangulare L. Seeds as Affected by Various Chemical and Physical Treatments

Three-month ‘old’ and ‘fresh’ seedsof Talinum triangulare were subjected to various treatmentsto induce early and rapid germination. Scarification and activated carbon were the most effective treatmentsin improving total germination in fresh seeds, while the 3 and5 per cent thiourea treatments were most effective in improvingtotal germination in old seeds. Activated carbon, scarificationand 5 per cent thiourea treatments enhanced early germinationin both old and fresh seeds. Cumulative percentage germinationwas very high in fresh seeds after scarification or after treatmentwith activated carbon and 5 per cent thiourea, and lowest inseeds treated with 3 per cent thiourea and hot water. In oldseeds, highest cumulative percentage germination was obtainedwith 3 and 5 per cent thiourea treatments and scarification.Generally, higher germination was obtained with fresh seedsthan with old seeds. Partial seed-coat removal and treatment with 5 per cent thiouriaresulted in a higher rate of and cumulative percentage germinationcompared with seeds with the coat partially removed but nottreated with thiourea. Constantly high temperature (34 °C) increased both rateand total germination compared with seeds planted at room temperature(20–23 °C). Treatments that did not induce germinationwere 1 per cent thiourea, H₂SO₄, cold water soaking at roomtemperature, 6 per cent hydrogen peroxide and soil planting.These treatments effected less than 3 per cent germination. Talinum triangulare L, seed scarification, activated charcoal, thiourea, germination     

Studies in Stomatal Behaviour: V. THE ROLE OF CARBON DIOXIDE IN THE LIGHT RESPONSE OF STOMATA

Experiments are described in which the responses of wheat stomatato carbon dioxide concentration (0·00, 0·01, 0·02,0·03 per cent.), light intensity (275, 625, 975 f.c.),and rate of air flow (2, 5, 12·5 l./hr.) were studied. Reduction of carbon dioxide concentration from 0·03 to0·01 per cent. resulted in marked stomatal opening; furtherreduction to 0·00 per cent, was accompanied by a slightbut not significant closure. These effects were found at alllight intensities and rates of flow, except at 975 f.c. with2 l./hr. air flow, where no effect of carbon dioxide concentrationwas detected. This last is attributed to excessive depletionof the carbon dioxide supply by assimilation. The apparent lowerlimit of 0·01 per cent, carbon dioxide causing maximalstomatal opening is discussed in relation to recent assimilationexperiments. Increase of light intensity caused considerable stomatal opening,this effect being as great with air of 0·00 and 0·01per cent. as with higher concentrations of carbon dioxide. Thissuggests an effect of light on stomatal movement other thanthat exerted indirectly through photosynthesis by the mesophylcells. Increased rate of flow of dry air caused closure of the stomata;this was shown to be a drying effect and was absent when moistair was used.     

Fat Metabolism in the West African Oil Palm (Elaeis Guineensis): PART I. FATTY ACID FORMATION IN THE MATURING KERNEL

Using a column chromatographic technique for the estimationand identification of fatty acids, a study has been made offat formation in developing Oil Palm kernels from 10 weeks afterpollination to full maturity (20 weeks), during which time thefat content may increase a hundredfold. Nuts from three differenttrees have been analysed and differences between these in ratesof maturation (as indicated by appearance of the endosperm)can be directly correlated with changes in character of theoil present. Amounts of reducing sugars, sucrose, and starch in the developingendosperm have also been followed, but these carbohydrates arepresent throughout in low concentration, and it is assumed thattranslocation from the rest of the plant to the developing kernelmust account for the major part of storage material. The mature kernel contains in its fat an unusual mixture ofeight different saturated fatty acids. The major such componentis lauric acid (46·1 to 49·5 per cent.) and thereare present two common unsaturated acids, oleic (15·7to 16·5 per cent.) and linoleic acid (0·7 to 3·1per cent.). At the earliest stage examined (10 weeks after pollination)all these acids are.present but in altered proportions, unsaturatedacids forming a larger fraction (36·5 to 81·2per cent., according to the tree investigated), and lauric acid(1·4 to 8·5 per cent.) a smaller. The results suggest that young kernels contain a small quantityof a largely unsaturated ‘protoplasmic’ fat, andthat at a certain stage in development some physiological changein the tissue results in the formation, in large quantities,of a new, highly saturated storage fat. No fatty acid interconversionscould be demonstrated although there is some suggestion thatoleic acid behaves anomalously. There is evidence that free fatty acids are not accumulatedprior to esterification.     

The Structure and Function of Pine Forest in Central Himalaya. I. Dry Matter Dynamics

The present study deals with structure and function of fourareas of Himalayan chir pine forest. Tree layer was monospecificon all sites with varied density and basal cover in the rangeof 540–1630 individuals per ha and 25·0–47·2m²ha^–1, respectively. Shrubs having low density were sparselydistributed. All allometric equations relating to biomass ofdifferent components, to circumference at breast height (cbh)were significant, with the exception of that for cone biomass.Total vegetation biomass (115–236 t ha^–1) was distributedas 113–283 t ha^–1 in trees. 0·56–0·82t ha^–1 in shrubs and 1·63–2·57 t ha^–1in herbs. Total forest floor biomass including herbaceous litterranged between 9·6 and 13·6 t ha^–1. Of thetotal annual litter fall (4·26–7·38 t ha^–1),60·3–75·1 per cent was distributed in leaflitter and 24·9–39·7 per cent in wood litter.Turnover rate of tree litter varied from 0·45 to 0·53,whereas rates for shrubs and herbs were assumed to 1. Net primaryproduction of total vegetation ranged between 9·91 and21·2 t ha^–1 year^–1, of which the contributionof trees, shrubs and herbs was 76·5– 88·1per cent 0·6–1·8 per cent and 11·3–21·5per cent, respectively. A compartment model of dry matter onthe basis of mean data across sites was developed to show drymatter storage and flow of dry matter within the ecosystem. Pinus roxburghii forest, biomass, litter fall, net primary production, compartmental transfer     

Influence of NaCl in the irrigation water on yield and quality of sweet pepper (Capsicum annuum)

Summary A field experiment was designed to determine the salt tolerance of three varieties of sweet pepper for paprika, studying the effects of four increasing levels of sodium chloride in the irrigation water (5, 10, 29 and 42 meq/l) on soil salinity, yields, and quality of the fruits. EC_5:1 and the soluble sodium and chloride contents increased with increasing salinity. The yields were reduced by 5 per cent for variety ‘Ramillete’, 19 per cent for ‘Tres cascos’, and 40 per cent for ‘Bola’ at the highest level. The fruit quality variables studied (colour index and chloride contents) differed with the variety. re]19750925     

Logarithmic Relationship between Moisture Content and Longevity in Sesame Seeds

The relationship between seed moisture content and seed longevityin sesame (Sesamum indicum L.) in hermetic storage at 50 °Cis logarithmic. The logarithmic relationship is maintained from15 per cent down to 2 per cent – the lowest moisture contenttested — but above 15 per cent this ‘air-dry’relationship no longer holds since further increase in seedmoisture content does not reduce longevity. Tentative estimatesof constant values for the improved seed viability equationare provided, and implications for long-term storage are discussed. Sesame, Sesamum indicum L., seed storage, improved viability equation, seed moisture content, seed longevity prediction     

The Induced Resistance Response of Carrot Root Slices to Heat-killed Conidia and Cell-free Germination Fluid of Botrytis cinerea Pers. ex Pers.: 2. Nuclear Migration, Nucleolar Volume and Uptake of Tritiated Uracil

Sixty-eight per cent of nuclei in the cells of the upper fourlayers of carrot slices treated with heat-killed conidia ofBotrytis cinerea for 6 h followed by inoculation with live sporesfor 18 h, migrated to the cell face nearest to the treated surface,compared with 46 per cent in cells of control slices showinga wound-healing response only. Nucleolar volumes in the surfacecell layers of control slices increased from a mean of 1.0 µm³to 3.8 µm³ over 24 h, and in ‘induced’ slicesto 7.28 µm³. Using a 40 min pulse of [5–³H]uracil,there was an increase within 15 h of slicing in the number oflabelled nuclei in cells from control slices undergoing healing.Within 8 h after treatment of slice surfaces with heat-killedconidia, there was an accelerated incorporation of label into‘nuclear’ RNA. Slices from roots cold-stored for12 months failed to show an induction response and nucleolarvolumes did not increase more than in control slices. Theseresults are discussed in relation to active defence mechanismsin plant tissue. Botrytis cinerea, carrot, induced resistance, nuclear migration, nucleolar volume, RNA incorporation     

Nitrogen Deficiency in Small Closed Communities of S24 Ryegrass. II. Changes in the Weight and Chemical Composition of Single Leaves During Their Growth and Death

Small communities of S24 ryegrass were grown under supplementarylights in a glasshouse at 20°C, and abundantly suppliedwith a complete nutrient solution containing 300 p.p.m. of nitrogen,until they had a leaf area index of 5 and were fully light intercepting.Half were then given a solution containing only 3 p.p.m. ofnitrogen (LN) while the rest were kept at 300 p.p.m. (HN). The HN plants subsequently produced marginally more leaves,which elongated more rapidly to a greater final length and area,on a third more tillers than did the LN plants. Leaves 5, 6 and 7 on the main stem were examined in more detail.In both the HN and the LN plants the d. wts of both laminaeand sheaths fell by about 30 per cent between their full expansionand death. Changes in acid extractable carbohydrate (AEC) verylargely accounted for the changes in leaf weight, particularlyin the LN plants. With increased nitrogen deficiency, AEC contentsrose from less than 10 per cent for leaf 5 to peak values of20 and 45 per cent for the lamina and sheath of leaf 7, as against10 and 15 per cent in the nitrogen sufficient leaves. Conversely,the nitrogen content of the deficient plants fell from valuesof 5·8 and 4·8 per cent for the lamina and sheathof leaf 5 to 3·0 and 1·2 per cent for leaf 7.It was striking that while the HN leaves lost nitrogen onlywhen they aged and died, the LN leaves started losing nitrogenbefore they had reached full expansion—70 per cent ofthe N initially present was remobilized by the time the leaveswere dead. The significance of these findinp to estimates of leaf deathand total biomass production in the field, and to our understandingof the achievement of ceiling yield, are discussed. Luliwn perenne, S24 ryegrass, carbohydrate content, nitrogen content, nitrogen deficiency     

Some Combined Effects of Size Grading and 'Hardening' Seed on the Establishment, Growth, and Yield of Four Varieties of Carrots

Carrot seed of four commercial varieties was separated intofractions by means of round-hole sieves. A fraction containingseed slightly larger than the average of the original samplewas selected and called graded seed. Graded and ungraded seedbatches were separately mixed with water in the ratio 10: 7by weight, kept covered in petri-dishes for 24 h at 20 °Cand then dried by exposure to the air at the same temperature.Three cycles of this ‘hardening’ treatment werecarried out. The varieties differed in their response, but ingeneral the combined hardening and grading treatment was oftenmore effective than the separate treatments and resulted ina 25 per cent increase in seedling weight, a rise in the fieldemergence percentage from 64 to 75 per cent, and increases inyield of 10 per cent above a control of 46 t ha^–1. Therapidity of seedling emergence was increased by the hardeningtreatment alone and the time over which the whole populationof seedlings emerged was reduced by the grading treatment only.Weather conditions caused a double ‘flush’ of germinationin part of the field experiment and the hardening treatmentreduced the proportion of undesirable second flush from 50 to30 per cent.