Effects of variation in ear temperature on growth and yield of spring wheat

Wheat plants were kept in a growth room at 15 ^oC from 7 days after an-thesis until maturity and their ears were warmed to 20 or 25 ^oC for various periods. Continuous warming initially increased the growth rate of the ear and decreased that of the stem, but hastened senescence of the ear and decreased final grain yield by decreasing dry weight per grain. Warming the ears increased the movement of ¹⁴C and nitrogen to them from the leaves and stem during the early stages of grain growth but decreased it later. Warming the ears for only the first 10 or 20 days also hastened ear senescence; grain yield decreased progressively with increase in duration of the warm period. All effects were greater at 25 than at 20 ^oC. The effects of changing ear temperature from 15 to 20 ^oC were independent of the temperature of the rest of the plant. Altering the humidity of the air around the ears by 4–7 mb at constant temperature had no effect on ear growth or senescence. Warming all of the plant except the ears from 15 to 20 ^oC increased ear growth slightly during early grain growth and decreased it later, irrespective of ear temperature: stem dry weight, leaf area and net photosynthetic rate of flag leaves and green stems were decreased and dark respiration rate of stems was increased.     

Nitrogen response surface models of zucchini squash,head lettuce and potato

Plants grown at 5 nitrate (N) levels ranging from 2–36 mmol L^–1 for lettuce and 2–43 mmol L^–1 for zucchini squash and potato were harvested over the growth period to maturity at a minimum of 2 week intervals. Gamma × cubic response surface models fitted actual dry matter growth data quite precisely (R²>0.98) from which growth and dry matter partitioning could be derived.Total dry matter growth was very responsive to N and maximum growth was predicted to occur at an N level of 14.2 mmol L^–1 for lettuce, 18.1 mmol L^–1 for zucchini squash and 11.6 mmol L^–1 for potato. Growth declined at higher N levels for all species. For zucchini squash, both high and low N levels which reduced growth increased partitioning of dry matter to fruit. For potato, partitioning of dry matter to tubers tended to increase at high levels of N, particularly at maturity. For lettuce, the N level producing the highest dry matter yield partitioned the highest ratio of dry matter to head.The highest fresh yields of zucchini squash fruit, lettuce head and potato tubers were recorded at N levels of 14, 5 and 11 and 7 mmol L^–1 respectively. The effect of N on quality followed a similar trend.     

Effects of daylength and day/night temperatures on growth and seed yield of cowpea cv. K 2809 grown in controlled environments

The effects of climatic factors on the growth, reproductive development and seed yield of cowpea (cv. K 2809) were investigated in controlled environment cabinets. Plants were grown to maturity in eight environments comprising all combinations of two day lengths (11 h 40 min and 13 h 20 min), two day (27 and 33 ^oC) and two night (19 and 24 ^oC) temperatures. The plants were nodulated (Rhizobium strain CB 756) and received 197 ppm N throughout growth. Treatments changed the time to the appearance of first flowers by a maximum of 6 days but the later-flowering plants more than doubled their dry weight during this period, so that effects on plant form and, ultimately, seed production were considerable. Warm nights (24 ^oC) not only hastened the onset of flowering but also enhanced dry matter production during the pre-flowering period; they did not extend the total growing period. Warm days (33 ^oC) did not enhance dry matter production but shortened the duration of the growing period by an average of 21 days (20%). Variation in final seed yield was mainly due to differences in the number of pods borne on branches. Warm days markedly decreased the number of pods per plant (an overall average reduction of 49%) as did warm nights in conjunction with the long (13 h 20) daylength. The number of seeds per pod was effected only by daylength (8.3 and 7.6 seeds in the long and short daylengths, respectively). Mean seed weight was decreased by 19% in warm as compared to cool nights but was increased by 18% in warm as compared to cool days. These responses are compared with those obtained with soyabean cv. TK5 in a previous experiment and are shown, in general, to be similar.     

Effects of variation in temperature and light intensity at different times on growth and yield of spring wheat

Spring wheat grown in pots outdoors was transferred to growth rooms for various periods to study the effect of increasing the temperature from 14-4 to 20-3 ^oC (Expt 1) or from day/night values of 15-0/15-2 to 20-0/15-2 ^oC (Expt 2) and of increasing the amount of visible radiation in a 16 h day from 424 to 792 J cm^-2 (Expt 1) or 374 to 740 J cm^-2 (Expt 2). There were no interactions between temperature and radiation. In Expt 1 neither the increase in temperature nor extra radiation, applied for 14 days immediately after the appearance of double ridges on the stem apex, or 14 days later, increased grain yield at maturity. Warmth early, but not late, increased dry weight, leaf area and the number of floret primordia immediately after treatment, but these effects had disappeared by anthesis, 30 days later. Dry weight but not leaf area was increased by extra radiation but the effects had disappeared 2 wk after treatment. An increase in temperature imposed for 16 days starting 5 or 21 days after anthesis (Expt 2) increased dry weight of the ear and decreased that of the rest of the plant immediately after treatment, and decreased leaf area at all times. When plants from the two temperatures were put together in the same conditions, ear growth of plants that had been in the warm was slower than that of plants from the cold treatment, so that the difference in ear weight observed after 16 days of treatment reversed and grain yield was decreased by warmth applied in either period; the component of yield decreased by warmth was grain size. Additional radiation in either post-anthesis period increased dry weight of all parts of the plant and had negligible effects on leaf area. Final grain yield was increased by c. 15% because the individual grains were larger. Early treatment also increased grain number slightly. The effects of treatment during the two post-anthesis periods were similar in size, and additive.     

Cucumber black root rot caused by Phomopsis sclerotioides

Phomopsis sclerotioides was proved to be a primary parasite attacking cucumber roots. Black pseudosclerotial and pseudostromatal lesions occurred more commonly at temperatures of c. 20 ^oC but at 10 ^oC unspecific light brown lesions predominated. Damage done by P. sclerotioides was minimal at soil temperatures of c. 20 ^oC, the aerial dry weights of parasitized plants, as percentages of those of the healthy controls, changing from c. 15% to c. 95% as soil temperatures increased from 12 to 20 ^oC. Root lesions were associated with root loss and decreased shoot growth. Severe attacks on young plants resulted in stunted growth and small, intensely green leaves. With less severe or later attacks, growth was initially indistinguishable from that of plants growing in uninfested soils until the rate of leaf senescence suddenly increased; these foliar symptoms temporarily simulated attack by vascular wilt fungi. Both sets of foliar symptoms were associated with appreciable yield losses.     

Bulbil production in Narcissus: the effect of temperature and duration of storage on bulb unit development and subsequent propagation by twin-scaling

The growth of bulb components and carbohydrate content of Narcissus bulbs was followed during storage at 5–30 ^oC, and the productivity of twin-scale propagules cut from bulbs after these storage treatments was studied. Growth of daughter bulb unit components was greatest during storage at 9–15 ^oC, and greatly inhibited at 30 ^oC. Concentrations of soluble sugars were highest following 30 ^oC storage, and higher in intermediate bulb scales than in outer or inner scales. Bulbil production on twin-scales was greatest on propagules cut from the intermediate scales, and in bulbs previously stored at 15 or 30 ^oC.     

The influence of temperature on the susceptibility of vine weevil, Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), larvae to Metarhizium anisopliae (Deuteromycotina: Hyphomycetes)

Mortality of Otiorhynchus sulcatus (Fabricius) larvae at 10^oC, 15^oC, 20^oC and 25^oC following treatment with 10⁷conidia ml“¹suspensions of six Metarhizium anisopliae (Metschnikoff) Sorokin isolates was temperature dependent. In all cases, the LT₅₀s were inversely related to temperature, but the nature of this response varied between isolates. Strain 101-82 was the most virulent isolate at 25^oC with an LT₅₀ of 3.7 days, but it was the least virulent isolate at 15^oC and it failed to kill any O. sulcatus larvae at 10^oC. In contrast, strain 159-83 had the lowest virulence at both 20^oC and 25^oC, whereas it was the most virulent isolate at 10^oC with an LT₅₀ of 20.0 days. The mortality rates followed a similar pattern and were positively related to temperature in all cases with the exception of strain 159-83 at 25^oC. Mycosis development was examined on larvae treated with strain 275-86 and significant differences were obtained between all four temperatures. Sporulation commenced after approximately 2.75 days at 25^oC, but took nearly 11 days at 10^oC. The infection rates also varied between temperatures; sporulation occurred on 98% of the treated larvae at 25^oC, but only on 93%, 87% and 49% of the larvae at 20^oC, 15^oC and 10^oC, respectively. The results of these bioassays demonstrate that temperature has a significant effect on the virulence of M. anisopliae. The differences between fungal strains also emphasises the importance of selecting isolates for specific situations on the basis of their temperature profiles.     

Effects of cottonseed hull levels in the diet and ageing time on visual and sensory meat acceptability from young bulls finished in feedlot

Cottonseed hulls are co-product of agribusiness that can be used in beef cattle rations, decreasing the cost of feed. The aim of this study was to evaluate the effects of different cottonseed hull levels, display and ageing times on visual and sensorial meat acceptability. Longissimus thoracis muscle from 30 crossbred young bulls finished on three high-grain diets (210, 270 or 330 g/kg of cottonseed hulls on dry matter, respectively) were visually evaluated during 10 days of display by 37 appraisers. Tenderness, flavour and overall acceptability from the three diets and three ageing times (1, 7 and 14 days) were evaluated by 120 consumers. On the visual study, time of display (P⩽0.001) was a more significant factor than diet. Cottonseed hull level had no effect on sensorial analyses, with tenderness acceptability improving with ageing time (P⩽0.001). Results indicate the possibility of using the three studied levels of cottonseed without damaging consumer meat acceptability.     

A preliminary evaluation of the use of microbial culture filtrates for the control of contaminants in plant tissue culture systems

The partitioning of carbon between reserve polysaccharide and alkaloid secondary products was investigated in batch cultures of transformed roots of Datura stramonium grown in media in which the carbon substrate concentration was held constant and the level of mineral nutrients was varied. The growth and accumulation of starch and hyoscyamine was examined in roots grown at temperatures of 20°C, 25°C or 30°C in media containing 5% sucrose and levels of mineral nutrients varying from 1/4 to twice the standard level of Gamborg's B5 salts. The dry matter content was highest (up to 15% w/w) in roots grown at either 20°C or 25°C in medium of the lowest ionic strenth (1/4 B5 salts) and decreased as the ionic strength was raised (down to 7% w/w with 2 B5 salts). Up to half of this decrease could be accounted for by loss of starch from the roots. At 20°C and 25°C, the starch content of the roots grown in medium of the lowest ionic strength (1/4 B5) was 40 mg g^-1 and 22 mg g^-1 fresh weight respectively but decreased to less than 1 mg g^-1 weight at either temperature when the ionic strength of the medium was raised to 2 B5. At 30°C, starch accumulation was severely inhibited in all media. In contrast, varying either the temperature or the ionic strength of the medium had only a small effect on hyoscyamine accumulation which remained at between 0.4–0.6 mg g^-1 fresh weight. Although increases in the level of mineral salts had little effect on the hyoscyamine content of the roots, total yields however, increased due to stimulation of growth. Time course experiments showed that cultures grown at either 20°C or 25°C continued to accumulate both starch and hyoscyamine into late stationary phase.     

Flavour profile of idli batter prepared from defined microbial starter cultures

Idli is a traditional cereal/legume-based naturally fermented steamed product with a soft and spongy texture which is highly popular and widely consumed as a snack food item in India. The predominant fermentation microflora comprises lactic acid bacteria and yeasts and causes an improvement in the nutritional, textural and flavour characteristics of the final product. The flavour profile of idli batter prepared with initial levels of 2 × 10⁴ c.f.u. g⁻¹ of Candida versatilis CFR 505 and 2 × 10¹ c.f.u. g⁻¹ of Pediococcus pentosaceus CFR 2123 in 500 g idli batter, packed in polyester polylaminate pouches and stored at 30 ± 2 °C was periodically analysed by GC-MS. The desirable flavour compounds such as ketones, diols and acids were found to be present upto 8 days of storage, whereas undesirable flavours like sulphurous and oxazolidone compounds, ethanone and thiazole appeared in the batter subsequent to 6 days of storage. The sensory attributes of idlis (final product) prepared from the stored batter related well to the determined flavour profile. The present study appeared to indicate that the flavour profile of traditional fermented foods can be a reliable qualitative and quantitative parameter for objective assessment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diagnosis of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK

Light leaf spot lesions were generally first observed as light green areas on leaves of UK winter oilseed rape crops in January or February and later became brittle and bleached. Elongated lesions, which were brown with indistinct edges, developed on stems in the spring and summer, when lesions were also observed on flower buds, pedicels and pods. Development of diagnostic white pustules (spore masses of Pyrenopeziza brassicae, which erupt through surfaces of infected tissues) for confirmation of light leaf spot infection on symptomless plants or plants with indistinct or ambiguous symptoms in the autumn, winter or spring was enhanced by incubating plants in polyethylene bags. In experiments with artificially inoculated plants, glasshouse-grown plants exposed in infected crops and plants sampled from crops, white pustules developed at all incubation temperatures from 2^oC to 20^oC on infected leaves of different cultivars. The period of incubation required before the appearance of pustules decreased as the time that had already elapsed since the initial infection increased. The longest periods of incubation were required at the lowest temperatures (2^oC or 5^oC) but leaves senesced and abscised from plants most quickly at the highest temperatures (15^oC or 20^oC), suggesting that the optimal incubation temperature was between 10^oC and 15^oC.     

Seasonal changes in sedimentation of particulate matter and lipid content of zooplankton collected by sediment trap in the Arctic Ocean off Axel Heiberg Island

Summary Sedimentation of particulate matter measured at a depth of 100 m varied from 0.2 to 6.0 mg dry weight m^-2 d^-1 over approximately monthly intervals between September 1986 and June 1987 on the continental shelf of the western Arctic Ocean north of the Canadian Arctic Islands. Detritus deposited during December and January, the period of maximum sedimentation, contained relatively low amounts of organic carbon and nitrogen (4.0% and 0.5% of dry weight, respectively) with a carbon: nitrogen ratio > 7. Maximum rates of organic carbon and nitrogen sedimentation (0.60 and 0.12 mg m^-2 d^-1, respectively) during February were associated with debris enriched with organic matter (organic carbon and nitrogen content of 17.0% and 3.4% of dry weight, C:N=5). Dry weight of macrozooplankton, predominantly Calanus hyperboreus and Metridia longa, separated from preserved trap contents, equalled or exceeded by up to an order-of-magnitude the weight of sedimented debris. Lipid content of CV and adult female stages of C. hyperboreus decreased from 46%–64% of dry weight in September to 20%–30% in January. Females of C. hyperboreus with lower lipid levels (7% of dry weight) between April and June were probably in a post-reproductive condition.     

Role of organophosphates in adaptations of an obligate water-breathing teleost (Tilapia nilotica L.) to hypoxia

Dry matter, total carbon (C), nitrogen (N) and phosphorus (P) content of mature bream from Lake Balaton were investigated and the quantities of N and P stored in the bream population and their possible removal by fishery were estimated. Carbon made up 43.3–44.8% of dry weight, N made up on average 10.6% of the dry weight of bream and P accounted for a further 2.7%. About 3.3 kg N ha^–1 and 0.9 kg P ha^–l are stored in the bream population. Approximately 0.5 kg N ha^–1 and 0.1 kg P ha^–1 are removed from the lake by bream harvest. Taking into account the total fish yield, the N removal is 2.1% and P removal 3.4% of the amount entering the lake.     

Effects of Indoleamines and Short Photoperiods on the Encystment of Gonyaulax polyedra

At a temperature of 15^oC, Gonyaulax polyedra responds to short days (light ≤ 10 h) by transition to the stage of a resting cyst. At 20^oC, even an lightdark (LD) cycle of 6:18 is incapable of inducing this process. In otherwise cyst-inducing conditions (15^oC; 10 h of light per day), an interruption of the scotophase by 2 h of light (LDLD 8:2:2:12 or 2:2:8:12) prevented encystment. Cyst induction is, therefore, initiated by a photoperiodic mechanism rather than by light deficiency. In Gonyaulax, photoperiodism may be mediated by the action of indoleamines. Melatonin, which exhibits a circadian rhythmicity in this organism, leads to encystment when given 1 h before lights-off in LD 11:13 at 15^oC, i.e., under otherwise noninducing conditions. Again, at 20^oC, melatonin is inefficient. Some analogues of melatonin, in particular, 5-methoxytryptamine and N,N-dimethyl-5-methoxytryptamine, and, at high concentrations, their respective precursors, serotonin and bufotenin, are capable of inducing cyst formation at 20^oC and in LD 12:12, whereas A'-acetyl-serotonin does not show this effect.     

Grain legumes and green manures as pre-rice crops in Northeast Thailand

The loss of dry matter (ash corrected), nitrogen (N) and carbon (C) from residues of several tropical legume species was monitored using litter bags in the field over a three-month period in Northeast Thailand. This work was linked to an experiment in a farmers' field where the residual benefits of the same legume species grown before flooded rice were measured. Litter bags were incorporated in the flooded rice plots at the same time as residue incorporation in the field experiment. The species studied were Sesbania rostrata, Aeschynomene afraspera and a multi-purpose cowpea variety (Vigna unguiculata cv KVC-7). In the case of S. rostrata the breakdown of fresh and oven-dried residues and of residues buried at depths of 2–3 cm and 15 cm was also compared.Although the initial N and C concentrations were similar for all the residues they exhibited differing dry matter, N and C loss patterns. With Sesbania rostrata, 80% of the N was lost from the residues after 20 days, however, there was only a 40% decline in C and weight during the same period. The rate and amount of N loss from Aeschynomene afraspera residues was much less than with S. rostrata, declining by approximately 35% during the first 40 days. There were marked differences in rates of N loss from stem and leaves of A. afraspera indicating that monitoring the decomposition of stem and leaves combined can be misleading. In multi-purpose cowpea, loss patterns of dry matter, N and C were all similar and 50–65% was lost after 40 days burial. There was little difference between breakdown of fresh and oven-dried S. rostrata residues nor were there noticeable differences between residues incorporated superficially (2–3 cm) and buried at 15 cm. Although both %N and lignin:N ratios correlated well with weight and N loss from the residues, this was only the case when leaf and stem material were analyzed separately for A. afraspera.Despite the slower rate and smaller total amount of N released from the A. afraspera residues compared with the S. rostrata residues, a similar amount and proportion (around 20 kg N ha^-1 or 22–28%) of the N was recovered from both residues by a crop of rice planted at the time of residue incorporation. This suggests a considerably higher use efficiency by rice of the N released from the A. afraspera residues (approximately 40%) compared with that for S. rostrata (30%).     

Growth and development of soyabean cv. TK5 as affected by tropical daylengths, day/night temperatures and nitrogen nutrition

Two experiments were done in Saxcil growth cabinets in order to investigate the effects of climatic factors and nitrogen nutrition on the growth, reproductive development and seed yield of soyabean cv. TK5. In the first, plants were grown to maturity in eight environments comprising all combinations of two short daylengths (11 h 40 min and 13 h 20 min), two day (27 and 33^oC) and two night (19 and 24^oC) temperatures. In the second, day temperature was kept at 33^oC but the night temperature was varied (19 and 24^oC) as was the mineral nitrogen supply (20 and 197 ppm N) to plants which were either inoculated or not with an effective single strain of Rhizobium. Taller, more branched, later flowering plants were produced in the longer daylength but seed yield was hardly affected because the components of yield did not all respond similarly. In the higher day temperature treatments seed yield per plant was reduced by half because all yield components were adversely affected - pods per plant by 34 %, mean seed dry weight by 24 % and seeds per pod just slightly. There was a marked effect of the higher night temperature which promoted early vegetative growth, induced early flowering and although the number of pods per plant was, overall, reduced by 48 %, seed yield per plant was little affected as mean seed dry weight was increased by 37 % and the number of seeds per pod was also increased slightly. Prior to flowering, nodulated plants obtained about two thirds of their total nitrogen requirement via direct uptake and one third through the symbiotic system. Vegetative dry weight and plant nitrogen content were increased by the higher mineral nitrogen level and, although height was slightly diminished, more branches were produced. Seed yield, however, was only slightly increased. These experiments have shown that night temperature is an environmental factor of major importance for the growth of this soyabean cultivar. They have provided, also, a more rational basis for interpreting seasonal variations in growth and seed yield of soyabean in the tropics where, clearly, day and night temperature effects can override those of daylength and nitrogen nutrition.     

Stemphylium botryosum f. lactucae- its developmentjn vifro and its pathogenicity to lettuce leaves

Stemphylium botryosum f. lactucae, incitant of a leaf-spot disease of stored lettuce, was found to be relatively restricted in its host range. Cross-inoculations with spore suspension of this fungus failed to induce symptoms in any of the host plants tested, except carrot. Among isolates of S. botryosum from various hosts, only the isolate from carrot induced slight symptoms on lettuce. While mycelial growth of the lettuce isolate was confined to the range 13–37 ^oC spores germinated at more extreme temperatures. The optimum temperature for germination and for radial growth on PDA was found to be between 25 and 30 ^oC. Wet spores were quickly inactivated at 50 ^oC, whereas more than 40 % of dry spores withstood a 24 h exposure to that temperature. Only the outer leaves of lettuce responded readily to inoculation with a spore suspension, the required incubation period being 3 days at 25 ^oC. Symptoms developed less readily on bruised leaves. Relative humidity approaching saturation was necessary for prompt and typical infection, notably during the 24 h following inoculation. Short dry periods (60 % r.h.) interposed at a later stage, while somewhat inhibitory, did not prevent infection.     

Phytophthora cryptogea root rot of tomato in rockwool nutrient culture:

The effect of root temperature on growth and yield of rockwool-grown tomato plants infected with Phytophthora cryptogea was investigated. Measurements of shoot and root growth were taken at high (25^oC) and low (15^oC) root temperatures during the generative phase of growth. The growth of roots of healthy and P. cryptogea-infected tomato plants in rockwool blocks was higher in plants grown with roots at 25^oC than at 15^oC after 60 days and a similar effect was found in slabs after 98 days. Under sub-optimal conditions for growth the disease became severe when root temperatures were low. Growth of roots was greatest when roots were maintained at a high temperature in combination with an ambient air temperature of c. 15^oC and the response was greater in cv. Counter than cvs Calypso and Marathon. Water-soluble carbohydrates of roots were higher in those produced in blocks than slabs and were reduced by infection compared to healthy plants with roots at 15^oC and 25^oC. Reduced transpiration rates were found 17 days after inoculation in symptomless plants grown at a root temperature of 25^oC. Infection, regardless of the temperature of the roots or cultivar, led to reduced stem growth. The plants grown at 25^oC were taller than those with a root temperature of 15^oC. After 9 wk of harvest, the cumulative fruit yields in infected cvs Counter and Calypso grown at 25^oC were comparable to that in healthy plants grown at either temperature and cumulative fruit numbers followed a similar pattern. High root temperatures led to delayed fruit ripening between weeks 3–10 and a larger number of unripe fruit. The weight of unripe fruit from infected plants grown at 25^oC at the terminal harvest was higher than from healthy plants with roots maintained at 15^oC.     

Seasonal CO2 exchange patterns of developing peach (Prunus persica) fruits in response to temperature, light and CO2 concentration

CO₂ exchange rates per unit dry weight, measured in the field on attached fruits of the late-maturing Cal Red peach cultivar, at 1200 μmol photons m^?2S^?1 and in dark, and photosynthetic rates, calculated by the difference between the rates of CO₂ evolution in light and dark, declined over the growing season. Calculated photosynthetic rates per fruit increased over the season with increasing fruit dry matter, but declined in maturing fruits apparently coinciding with the loss of chlorophyll. Slight net fruit photosynthetic rates ranging from 0. 087 ± 0. 06 to 0. 003 ± 0. 05 nmol CO₂ (g dry weight)^?1 S^?1 were measured in midseason under optimal temperature (15 and 20°C) and light (1200 μmol photons m^?2 S^?1) conditions. Calculated fruit photosynthetic rates per unit dry weight increased with increasing temperatures and photon flux densities during fruit development. Dark respiration rates per unit dry weight doubled within a temperature interval of 10°C; the mean seasonal O₁₀ value was 2. 03 between 20 and 30°C. The highest photosynthetic rates were measured at 35°C throughout the growing season. Since dark respiration rates increased at high temperatures to a greater extent than CO₂ exchange rates in light, fruit photosynthesis was apparently stimulated by high internal CO₂ concentrations via CO₂ refixation. At 15°C, fruit photosynthetic rates tended to be saturated at about 600 μmol photons m^?2 S^?1. Young peach fruits responded to increasing ambient CO₂ concentrations with decreasing net CO₂ exchange rates in light, but more mature fruits did not respond to increases in ambient CO₂. Fruit CO₂ exchange rates in the dark remained fairly constant, apparently uninfluenced by ambient CO₂ concentrations during the entire growing season. Calculated fruit photosynthetic rates clearly revealed the difference in CO₂ response of young and mature peach fruits. Photosynthetic rates of younger peach fruits apparently approached saturation at 370 μl CO₂1^?2. In CO₂ free air, fruit photosynthesis was dependent on CO₂ refixation since CO₂ uptake by the fruits from the external atmosphere was not possible. The difference in photosynthetic rates between fruits in CO₂-free air and 370 μl CO₂ 1^?1 indicated that young peach fruits were apparently able to take up CO₂ from the external atmosphere. CO₂ uptake by peach fruits contributed between 28 and 16% to the fruit photosynthetic rate early in the season, whereas photosynthesis in maturing fruits was supplied entirely by CO₂ refixation.     

The effect of temperature on the rate of sprout growth and development within stored onion bulbs

In order to understand better the effects of storage temperature on the time to visible sprouting in stored onions, sprout growth was measured by regularly dissecting samples from bulbs stored at 1, 10, 15 or 25°C for 243 days. The dry-weight of the shoot or sprout within stored onion bulbs increased exponentially with time. The rate of increase of sprout dry weight, as well as the rate of leaf initiation by the shoot apex was faster at 17° than at 10 or 25°C, and almost zero at 1°C. The rate of loss of dry weight from storage tissue was similar at 17°C and 25°C but slower at 10°C and slower still at 1°C.