Changes in the Endogenous Growth Regulators in Bulbous Iris in Bulb-forming and Nonbulb-forming Aspects

Bulblets of 3–4 g of Dutch iris (Iris hollandica) cv.Dominator stored at 20°C and then grown at 15°C developedonly three or four leaves and bulbs formed at the base of eachleaf, whereas when grown at 25°C, they continued to growvegetatively with the development of 10 true leaves and didnot form any new bulb. This demonstrated that bulb formationin bulbous plants can be controlled by environmental factors.The levels of both abscisic acid and auxin activities increasedduring growth under the bulb-forming condition whereas onlyauxin activity increased under the nonbulb-forming condition.The coexistence of both abscisic acid and auxin seems to beessential in the processes of bulb formation. (Received August 22, 1980; Accepted November 26, 1980)     

The Effect of Cooling on Photosynthesis, Amounts of Carbohydrate and Assimilate Export in Sunflower

Sunflower plants (Helianthus annuus L.) grown at 30°C werecooled to 13°C in the light in atmospheric CO² or low CO²,or in darkness. Photosynthetic rate at 30°C after coolingwhole plants in atmospheric CO² for 12 h during a photoperiodwas significantly lower than at the start of the photoperiodcompared to plants cooled at low CO², those cooled in the darkand those maintained at 30°C. Amounts of sucrose, hexosesand starch in leaves at 13°C increased throughout a 14 hphotoperiod to levels higher than in leaves at 30°C, whereamounts of sucrose and hexoses were stable or falling after4 h. Carbohydrate accumulation at 13°C during this photoperiodwas more than twice that at 30°C. After three photoperiodsand two dark periods at 13°C carbohydrate levels in leaveswere still as high as at the end of the first photoperiod, butless carbohydrate accumulated during the photoperiods than duringthe first photoperiod, and more was partitioned as starch. Amountsof soluble carbohydrate in roots were greater after 14 h at13°C than in roots of plants at 30°C. Loss of ¹⁴C fromleaves at 30°C as a proportion of ¹⁴CO2 fixed by them at30°C, decreased after exposure of plants to 13°C inthe light for 30 min prior to ¹⁴CO²feeding. Results indicatean effect of cold on the transport process that was light-dependent.It is inferred that the reduction in the proportion of ¹⁴C lostfrom leaves after 10 h cooling was due to reduced sink demand,whereas the rise in the proportion of ¹⁴C lost from leaves after24 h reflects reduced photosynthetic rate. The coincidence ofreduced photosynthetic rate with raised carbohydrate levelsin leaves maintained at 30°C throughout, whilst the restof the plant was cooled to 13°C in the light implies feedbackinhibition of photosynthesis. This may reduce the imbalancebetween source and sink in sunflower during the first days oflong-term cooling. Key words: Temperature, carbon export, carbohydrates, photosynthesis, sunflower     

The Rate of Transport of Natural Auxin in Woody Shoots

A method is described for the estimation of the rate of movementand the quantity transported of the natural growth hormone instandard isolated segments of apple shoots. During controlledstorage diffusible auxin is collected, and later by dividingthe standard length of stem into small sections the locationof the auxin front is determined, from which the rate of transportis deduced. Temperature markedly affects both rate of transportand amount of auxin transported (cf. van der Weij, 1932), amaximum occurring at 27–30° C.; followed by a rapidfall to zero. The total diffusible auxin in a given length ofstem is not affected by storage temperatures below 30° C.but falls to zero at 42° C. The rate of transport and amounttransported are proportional to the oxygen tension over therange 0 to 5 per cent. O₂, and there is some evidence for destructionof auxin in tensions below 2 per cent.     

Changes in the Distribution of 14C-Labelled Assimilates in Sugar-beet with Variation of Temperature

Plants were allowed to assimilate ¹⁴CO₂ for 30 min at 5, 15,25, and 35 °C. The changes in ¹⁴C content of a mature expandedleaf (Leaf 4), young apical leaves, and storage root, were sequentiallyfollowed over a subsequent period of 24 h in continuous light.In a second experiment plants were transferred after ¹⁴CO₂ assimilationto temperatures of 10, 18, 26, and 34 °C, and the partitionof ¹⁴C between the ethanol-soluble and ethanol-insoluble fractionsof the roots and leaves was followed over a period of 72 h. The specific activities of the apical leaves and of the storageroot increased to a maximum 2 h after labelling at 25 °C,4 h at 15 and 35 °C, and 6 h at 5 °C suggesting thatthe optimum temperature for translocation of photosynthate wasabout 25 °C. The ¹⁴C partition to ethanol-soluble and ethanol-insoluble fractionsof the roots and leaves was largely attained in. 9 h. Littlerepartition of ¹⁴C assimilate fractions occurred as a resultof temperature change or growth. Root ethanol-insoluble activity,however, did increase significantly over the 72-h period : possiblecauses of this slow incorporation and their relevance to themechanism of sugar storage are discussed.     

Growth Hormone Changes in Chrysanthemum morifolium: Effects of Environmental Factors Controlling Flowering

Simultaneous quantitative analyses have been made of the endogenouslevels of auxin- and gibberellin like substances, growth inhibitors,and auxin-oxidizing enzyme activity in the cold-requiring Chrysanthemummorifolium cv. Sunbeam subjected to different daylength, lightintensity and temperature regimes known to affect flowering.While little hormone or enzyme activity was found in extractsfrom unvernalized plants, a striking rise in auxin-oxidizingenzyme activity occurred rapidly after the end of cold treatment.Increased auxin activity was also recorded shortly after vernalization.At 28 °C both enzyme and auxin activity declined over aperiod of 3–4 weeks; at 20 °C this response was delayed.Gibberellin activity at 28 °C rose steeply about 2 weeksfrom vernalization and declined several weeks later; at 20 °Ca similar response was less marked. Low light intensity treatment,which may have increased endogenous auxin levels, or exogenousauxin application reduced gibberellin-like substance levelsand cause d devernalization.Phosphon D treatment also loweredgibberellin levels and prevented flowering. An extract fromvernalized plants containing gibberellin-like substances intensifiedthe flowering of partially vernalized test plants. Persistenceof high auxin activity in vernalized plants on long days wasassociated with failure to form normal flower buds. Stem elongationrates correlated in general with levels of endogenous auxin-and gibberellin-like substances. Significant amounts of an abscisin-likeinhibitor were found in extracts of flower buds. The mechanismof natural devernalization is discussed in relation to theseobservations.     

Auxin-promoted Transport of Metabolites in Stems of Phaseolus vulgaris L.: SOME CHARACTERISTICS OF THE EXPERIMENTAL TRANSPORT SYSTEMS

Indol-3yl-acetic acid (IAA) applied to sterns of Phaseolus vulgarisseedlings, decapitated above primary leaves, enhanced the mobilizationof ¹⁴C-metabolites to the treated stumps and this effect wasapparent within 3–6 h of applying the hormone. More than90 per cent of the total ¹⁴C-activity transported to the stumpswas detected in the alcohol-soluble extracts. In all treatments,less than 5 per cent of the ¹⁴C-photosynthate exported fromthe primary leaves was translocated upwards. Accumulation of¹⁴C-activity was also increased when the IAA was applied laterallyto intact internodes. This effect was obtained when ¹⁴C wassupplied either above or below the point of hormone application.By selective heat girdling, it was shown that the auxin affected¹⁴C transport when either the root ‘sink’ was removedor transpiratory flow of water through the treated internodewas maintained. Decapitated stems treated with plain lanolinfor 3 d were found to retain their responsiveness to auxin interms of enhanced metabolite transport. Heat-girdling experimentsand estimates of ¹⁴C transport velocity suggested that mostof the ¹⁴C movement was restricted to the phloem of treatedstumps. Similar effects of IAA on a transport in excised stemsegments of Phaseolus vulgaris were observed.     

The Stimulatory Effect of Indole-3-Acetic Acid on the Uptake of Amino-Acids by Tissue 1Helianthus annuus

Indole-3-acetic acid was observed to bring about a prompt andmarked increase in the amount of ¹⁴C accumulated by segmentsof sunflower hypocotyl from solutions of labelled glutamic acid,glycine, and lysine. The curve relating magnitude of effectto indole-3-acetic acid concentration followed the comparablecurves for water uptake and extension growth. The accumulation of ¹⁴C was related to the external concentrationof glutamic acid by a curve which departed only slightly fromlinearity. The percentage increase in ¹⁴C accumulation broughtabout by auxin did not decline to any appreciable extent withincreasing external concentration of glutamic acid. Under nitrogen the amount of ¹⁴C taken up from solutions oflabelled glutamic acid in 1·75 hour was cut down by approximatelyone-third, and the auxin effect was abolished. The Q₁₀ for ¹⁴Caccumulation between 16° C. and 26° C. was 1·2in the absence of indole-3-acetic acid, and was 1·3 inits presence. When net water uptake was eliminated by the addition of mannitolto the external solution, ¹⁴C accumulation in auxin-free mediawas not depressed. The percentage increase in ¹⁴C accumulationbrought about by auxin, however, was markedly reduced. The fate of the ¹⁴C accumulated was investigated by means ofchromatography on resin columns and on filter paper. About 30–40percent, of the ¹⁴C was in the form of glutamic acid after approximatelya hours' treatment. No marked difference in the level of glutamicacid was observed between auxin-treated and control segments.The effect of auxin was more evident on the amounts of otherradioactive derivatives, as yet unidentified. It was observed that, not only was the amount of CO₂ evolvedin respiration higher in the presence of indole-3-acetic acid,but that this CO₂ was richer in ¹⁴C, i.e. in auxin-treated tissueglutamic acid formed a larger proportion of the substrate respired. The possible implications of these observations are discussed.It is pointed out that indole-3-acetic acid may have achievedits effect by stimulating a transfer process, by lessening adiffusion resistance, or by promoting a process or processeswhich, by removing free amino-acids within the cell, maintainan inward diffusion gradient.     

Changes in Tissue Freezing in Senecio vulgaris infected by Rust (Puccinia lagenophorae)

Freezing of healthy and rust (Puccinia lagenophorae) infectedleaves of Senecio vulgaris was compared calorimetrically bythermal analysis. In fully expanded leaves the threshold freezingtemperature was in the range –6.8 to –8.4 °Cin controls but –3.0 to –5.1 °C in leaves withsporulating rust sori. Comparable values in expanding leaveswere –5.0 to –8.9 °C and –3.9 to –6.7°C for healthy and rusted tissues, respectively. The bulktissue freezing point was between –1.0 and –4.0°C in both fully expanded and expanding healthy leaves,and was increased by infection by between +0.2 and 2.5 °C.Whereas healthy leaves supercooled by 3.1–5.8 °C,rusted leaves supercooled by only 1.8–4.9 °C Supercoolingof control leaves was reduced by dusting with aeciospores, particularlywhen leaves were wounded to simulate the rupture of the surfacecaused by sporulation, but wounding alone had no significanteffect. Supercooling of distilled water was also significantlyreduced by aeciospores, suspended at a concentration of 10⁵spores ml^–1. It is concluded that rust-induced changes in leaf freezing inS. vulgaris grown in controlled environments were due to anincrease in the number of sites for ice nucleation, caused bythe presence of the aeciospores, and increased penetration ofice into internal tissues, resulting from damage to the cuticleand epidermis. Although data for frost resistance obtained inthe growth-room are similar to previous field observations,the role of the above mechanisms under field conditions remainsunproven. Senecio vulgaris (groundsel), Puccinia lagenophorae (rust), low temperature, freezing resistance     

Axillary Bud Inhibition Induced by Young Leaves or Bract in Euphorbia pulcherrima Willd

In plants held under long days in the vegetative stage, youngexpanding leaves of poinsettia (Euphorbia pulcherrima Willd.‘Brilliant Diamond’) are the main source of axillarybud inhibition, while the apical bud, which includes the meristem,primordial leaves and small unfolded leaves, is a secondaryinhibition source. Removal of these expanding leaves resultedin rapid release and growth of axillary buds. Decapitation ofthe apical bud resulted in delayed axillary bud release. Inreproductive plants kept in short days, the pigmented bractsare the primary source of axillary bud inhibition and the cyathiaare the secondary source. Applications of NAA —substitutedfor both young leaves and bract inhibition — maintainedapical dominance. The concentration of endogenous auxin washighest in the apical bud. However, when calculated on wholeorgan basis the auxin level was greater in young developingvegetative leaves and in reproductive bracts than in the apicalbud. Euphorbia pulcherrima Willd, apical bud, apical dominance, auxin, correlative inhibition, cyathia, poinsettia, IAA, NAA     

A Relationship between Membrane Permeability and Ethylene Production at High Temperature in Leaf Tissue of Phaseolus vulgaris L.

Leaf discs cut from primary leaves of Phaseolus vulgaris L cvMasterpiece were incubated at temperatures higher than the growthtemperature of 25 °C Both basal and wound ethylene productionincreased up to temperatures of 35–37 5 °C, thereafterdeclining rapidly There was no detectable ethylene productionat temperatures above 42 5 °C Exposure of leaf discs tohigh temperature for 60 mm resulted in a large production ofwound ethylene when they were returned to 25 °C The magnitudeof ethylene production was related to the initial incubationtemperature as was the length of the lag period before maximumproduction was achieved The results are discussed in relationto the requirement for continued membrane integrity for ethyleneproduction ethylene, temperature, membrane permeability, Phaseolus vulgaris L, dwarf bean     

The Freezing Response of an Arctic Cushion Plant, Saxifraga caespitosa L.: Acclimation, Freezing Tolerance and Ice Nucleation

Cold hardiness in actively growing plants of Saxifraga caespitosaL., an arctic and subarctic cushion plant, was examined. Plantscollected from subarctic and arctic sites were cultivated ina phytotron at temperatures of 3, 9, 12 and 21 °C undera 24-h photoperiod, and examined for freezing tolerance usingcontrolled freezing at a cooling rate of 3–4 °C eitherin air or in moist sand. Post-freezing injury was assessed byvisual inspection and with chlorophyll fluorescence, which appearedto be well suited for the evaluation of injury in Saxifragaleaves. Freezing of excised leaves in moist sand distinguishedwell among the various treatments, but the differences werepartly masked by significant supercooling when the tissue wasfrozen in air. Excised leaves, meristems, stem tissue and flowerssupercooled to –9 to –15 °C, but in rosettesand in intact plants ice nucleation was initiated at –4to –7 °C. The arctic plants tended to be more coldhardy than the subarctic plants, but in plants from both locationscold hardiness increased significantly with decreasing growthtemperature. Plants grown at 12 °C or less developed resistanceto freezing, and excised leaves of arctic Saxifraga grown at3 °C survived temperatures down to about –20 °C.Exposure to –3 °C temperature for up to 5 d did notsignificantly enhance the hardiness obtained at 3 °C. Whenwhole plants of arctic Saxifraga were frozen, with roots protectedfrom freezing, they survived –15 °C and –25°C when cultivated at 12 and 3 °C, respectively, althougha high percentage of the leaves were killed. The basal levelof freezing tolerance maintained in these plants throughoutperiods of active growth may have adaptive significance in subarcticand arctic environments. Saxifraga caespitosa L., arctic, chlorophyll fluorescence, cold acclimation, cushion plant, freezing stress, freezing tolerance, ice nucleation, supercooling     

The Responsiveness to Temperature of the Extension Rates of Leaves of Wheat Growing in the Field under Different Levels of Nitrogen Fertilizer

The response of the rates of extension (LER) of wheat leaves(Triticum aestivum cv. Gamenya) to temperatures maintained fora short period was measured by changing the temperature of theextension zone and recording the changes in leaf length. Therange of temperatures used was from 4-38 °C. The LER ofall leaves responded to increases in temperature as field temperatureswere suboptimal. The data obtained from several series of measurementsover different ranges of temperature were combined to producea general response curve. The minimum temperature for LER wasconsidered to be approximately 0 °C, the optimum was 28.4°C, while the maximum was in excess of 38 °C. The responsivenessof LER to temperature, measured by the Q₁₀, declined exponentiallyfrom >6 at 5 °C to 2 at 20 °C. The Q₁₀ at 15 °Cwas not affected by nitrogen supply.     

Growth of White Clover, Dependent on N2 Fixation, in Elevated CO2 and Temperature

Clonal plants of white clover (Trifolium repens L ), whollydependent on N₂ fixation, were grown for 6 weeks in controlledenvironments providing either (C680 regime) 23/18 °C day/nighttemperatures and a CO₂, concentration of 680 µmol mol^–1,or (C340 regime) 20/15 °C day/night temperatures and a CO₂,concentration of 340 µmol mol^–1 During the firsthalf of the experimental period the C680 plants grew fasterthan their C340 counterparts so that by week 3 they were twicethe weight this 2 1 superiority in weight persisted until theend of the experiment The faster initial growth of the C680plants was based on an approx 70 % increase in leaf numbersand an approx 30 % increase in their individual area Initially,specific leaf area (cm2 g^–1 leaf) was lower in C680 thanin C340 leaves but became similar in the latter half of theexperiment Shoot organ weights, including petioles and stolons,reflected the C680 plant's better growth in terms of photosyntheticsurface Throughout, C680 plants invested less of their weightin root than C340 plants and this disparity increased with timeAcetylene reduction assays showed that nitrogenase activityper unit nodule weight was the same in both C680 and C340 plantsBoth groups of plants invested about the same fraction of totalweight in nodules Nitrogen contents of plant tissues were similarirrespective of growth regime, but C680 expanded leaves containedslightly less nitrogen and their stolons slightly more nitrogenthan their C340 counterparts However, C680 leaves containedmore non-structural carbohydrate Young, unshaded C680 leavespossessed larger palisade cells, packed more tightly withinthe leaf, than equivalent C340 leaves The reason for the C680regime's loss of superiority in relative growth rate duringthe second half of the experiment was not clear, but more accumulationof non-structural carbohydrate, constriction of root growthand increased self-shading appear to be the most likely causes Trifolium repens, white clover, elevated CO₂, elevated temperature, growth, N₂ fixation, leaf structure     

The Effects of Position and Temperature on the Expansion of Leaves of Vicia faba L.

The growth in area of the first eight leaves of broad bean plantswas investigated in growth room experiments. Plants were grownat either 20 or 14 °C or transferred from 20 to 14 °C.Rates of leaf appearance and unfolding increased with temperature.The duration of growth of a leaf increased with leaf numberfor the first five leaves and then remained constant The meangrowth rate declined or remained constant with increasing leafnumber Durations of growth were shorter and growth rates largerat 20 °C than at 14 °C Plants responded immediatelyto the change in temperature Final areas of leaves which expandedafter transfer from 20 to 14 °C were larger than those grownat 20 °C Vicla faba L., broad bean, leaf expansion, temperature responses     

Some Effects of the Environment on the Temperature of Tobacco Leaves in Field Plots in Rhodesia

Temperatures of field-tobacco leaves, at different heights andorientated in different directions, were continuously recordedduring three periods with resistance thermometers in the proximaland distal parts of the upper tissue of the main leaf veins.The temperature of leaves, relative to that of the air at thesame height (RLT), was positive during daylight and negativeat night; sheltered leaves were sometimes warmer than the airall day. Maximum and minimum individual RLT values, between09.00 and 16.00 hours, were +18° C and –4° C atair temperatures of 25–28° C. At night, maximum andminimum RLT values were between +0.2° and –3.0°C. Leaves facing NE were warmer in the morning thatn those facingNW or SW, but were cooler in the afternoon. Distal parts ofleaves were cooler than proximal parts and upper leaves werecooler than lower ones at night: Mean daily maximum RLT wasgreatest in lower leaves and mean daily minimum RLT was smallestin upper ones. During daylight, exposure to solar radiation had the greatesteffect on RLT: proximal parts of leaves were affected most byair temperature and humidity, and distal parts by cloud cover.At night, and often in the evenings, RLT depended largely oncloud, humidity, and leaf cover, all of which affected re-radiation:correlations between RLT and these environmental factors werefound more often with distal than with proximal parts of leaves.     

High Temperature Sensitivity of Auxin-induced Ethylene Production in Mung Bean Hypocotyl Sections

High temperature sensitivities of IAA-induced and 1-aminocyclopropane-1-carboxylicacid (ACC)-dependent ethylene production in etiolated mung bean(Vigna radiata [L] Wilczek) hypocotyl sections were comparedat 30,40, 42.5°C. When ethylene production at 30°C wastaken as control, IAA-induced production at 40°C was firstenhanced and then suppressed after 3 h, whereas ACC-dependentproduction was enhanced two-fold throughout the 8 h experimentalperiod. However, when hypocotyl sections treated with 1 mM ACCat 30°C for several hours were transferred to 40°C,the ACC-dependent production rate fell below that at 30°C.An initial transient enhancement of IAA-induced ethylene productionat 40°C was supported by increased ACC synthase activityand thus by ACC content. At 42.5°C, both IAA-induced andACC-dependent production were almost completely suppressed.The results indicate that auxin-induced ethylene productionis affected by high temperatures in two different steps: a)at 40°C, the auxin action gradually deteriorates althoughconversion of ACC to ethylene is not affected at all, and at42.5°C, the conversion is nearly completely suppressed. (Received July 8, 1985; Accepted January 24, 1986)     

Somatic embryogenesis in Agave tequilana Weber cultivar azul

Somatic embryogenesis was achieved from leaves of Agave tequilana Weber cultivar azul utilizing MS medium supplemented with L2 vitamins and the addition of cytokinins: 6-benzylaminopurine (BA), 1-phenyl-3(1,2,3-thiadiazol-5-yl)urea (TDZ), 6-(γ-γ-dimethylamino)purine (2ip) and 6-furfurylaminopurine (KIN), combined with the auxin 2,4-dichlorophenoxyacetic acid (2,4-D). Differences among the six genotypes studied with regard to their embryogenic response in culture were found. Embryos produced by genotype S3 under a hormone regime of high cytokinin (44.4 to 66.6 μM BA) compared to auxin (4.5 μM 2,4-D) contained chlorophyll, whereas those produced when auxin was high compared to cytokinin (9.0 and 13.6 μM 2,4-D and 1.3 and 4.0 μM BA, respectively) were whitish and morphologically similar to their zygotic counterparts. Somatic embryos matured and germinated after transferring the embryogenic calli to maturation and germination medium without growth regulators and enriched with organic nitrogen. Microscopic observations demonstrated a unicellular origin for production of indirect somatic embryos.     

Changes in the Soluble Protein and Free Amino Acid Content of Chill-Sensitive and Chill-Resistant Plants During Chilling and Hardening Treatments

The effects of low temperature (5 °C and 12°C) and droughttreatments on leaf soluble protein content and free amino acidcontent have been investigated in four species, which were rankedaccording to chilling-sensitivity: pea (chill-resistant), mungbean (highly chill-sensitive), and tomato and french bean (intermediatechilling-sensitivity). Drought treatment caused a 30–40% decrease in proteinlevels, and in all but the mung bean, a 100–200% increasein free amino acid concentration. Four days chilling at 5°C,85% r.h. caused leaf water content to decrease by almost 50%in the mung bean, but by only approximately 6–7% in theother three species. During this treatment the leaf solubleprotein content decreased in all four species although the decreasewas greatest and most rapid in the mung bean, commencing with8 h of chilling (coinciding closely with the onset of waterloss), and decreasing by over 80% after 4 d. In the chill-sensitivespecies (but not in the pea) the decrease in protein contentwas accompanied by an increase in free amino acid content. However,on a mgg^–1 dry wt. basis, this increase was insufficientto account for all the protein lost. When plants of each specieswere chilled at 5°C, 100% r.h., water loss was greatly reducedor prevented and there was no significant decrease in leaf solubleprotein. It is concluded that the protein decrease which occurredat 5°C, 85% r.h., was a response to water loss and not thedirect result of low temperature. However, chilling at 100%r.h. did cause an increase in free amino acid content of thechill-sensitive species, suggesting that this was a direct responseto low temperature. Although drought treatment caused a 6–20 fold increasein free proline content in the leaves of the four species examined,chilling (5°C) and chill-hardening (12°C) caused littlechange in free proline content, indicating that the accumulationof this ‘protective’ amino acid is unlikely to contributeto the effectiveness of the chill-hardening treatment. Key words: Low Temperature, Drought, Leaf soluble protein.content, Amino acids     

Further Effects of Light Intensity, Carbon Dioxide Concentration, and Day Temperature on the Growth of Chrysanthemum morifolium cv. Bright Golden Anne in Controlled Environments

In earlier work the effects of light intensity over the range31 to 250 J cm^–2 day^–1 and carbon dioxide concentrationfrom 325 to 900 ppm with 8-h days at 18.3 °C and 16-h nightsat 15.6 °C were described. The present paper is concernedwith three further experiments with light levels up to 375 Jcm^–2 day^–1 (which corresponds to the daily totalin a glasshouse in southern England in early May or August andthe intensity is approximately that of mid-winter sunshine),carbon dioxide concentration up to 1500 ppm, and day temperaturesof 18.3 to 29.4 °C. Final plant weight was increased by light over the range 125–375J cm^–2 day^–1 and by carbon dioxide over the range325–900 ppm, with positive interaction between them; thisinteraction was increased by raising the temperature to 23.9°C and somewhat more at 29.4 °C day temperature. Leaf-arearatio and specific leaf area were reduced by increasing eitherlight or carbon dioxide but there was little effect of temperature.Leaf-weight ratios were uniform within experiments but therewere small consistent differences between one experiment andthe other two which also affected leaf-area ratios. Mean unit leaf rate was scarcely affected by day temperatureover the range investigated. There were the usual increasesdue to increased light and carbon dioxide concentration anda consistent difference in absolute value between one experimentand the other two. These differences in mean unit leaf rateare illustrated in detail in the ontogenetic trend of unit leafrate and plant size. Lower unit leaf rates were to a considerableextent compensated for by increased leaf-area ratios in theusual way. Despite the substantial differences in day temperature the specificwater contents (g water g dry weight^–1) differed little,showing in the majority of cases higher values in the highertemperature for otherwise similar treatment combinations. Flower development was somewhat delayed at 23.9 °C day temperature,and substantially so at 29.4 °C. Lateral branch length wasincreased at 23.9 °C and excessively so at 29.4 °C.This reveals quite clearly that a temperature optimum for vegetativegrowth may not be the optimum for flowering performance norproduce a desirable plant shape. Despite the marked effects of temperature on rate of flowerdevelopment, the relationship between flower development andthe ratio of flower to total weight was the same for all treatmentcombinations in all three experiments and coincident with thatreported earlier. Gasometric determinations indicated that respiratory loss bythe whole plant was a smaller proportion of net photosyntheticgain at a temperature of 29.4 °C than at 18.3 °C andwas likewise a smaller proportion at 1500 ppm carbon dioxidethan at 325 ppm. If photorespiration of leaves is assumed tobe as great as their dark respiration, the respiratory lossesare in the range of 31–50 per cent of the gross gain.Greater rates of photorespiration would increase the proportionaterespiratory loss.