The natural cross-pollination of crop plants with particular reference to the radish

Experiments were carried out to determine what degree of intervarietal cross-pollination occurs when two radish varieties are grown at varying distances apart. The varieties chosen were Icicle and Scarlet Globe. Hybrids are distinctive; thus crossing is readily determined.
In closely planted experiments, where one half of the plot was Icicle and the other half Scarlet Globe, the amount of intercrossing ranged from 30 to 40 % at a distance of 9 in. to an average of about 1 % at 15 ft. Intercrossing decreased fairly regularly and rapidly with distance.
Single plants of Icicle were run out from plots of Scarlet Globe; in 1941 at distances from 9 in. to 95 ft. and in 1942 from 9 in. to 408 ft. In the plants near the red plots crossing was approximately 100 %. In 1941 there was a regular and rapid fall with distance and intervarietal crossing stopped at 95 ft. In 1942 the plots were closer to beehives; intercrossing was less regular and extended farther than in 1941, but beyond 240 ft. it was only 0.1%, and in an all-white plot 360 ft. from a red plot with no intervening stringer plants it was nil.
Given a mass of plants and a profusion of flowers, bees confine their flower visiting to a small area. When radishes are grown in quantity 300 ft. guards against contamination of stock due to intervarietal crossing. If only small numbers are grown intercrossing is likely to occur over a greater distance.     

The effect of cadmium and lead on the growth of two species of marine phytoplankton with particular reference to the development of tolerance

Decreases in salinity (<10%) increased the growth rates ofPhaeodactylum tricornutum and Dunaliella tertiolecta. Increasinglevels of cadmium (1–50 ppm (mg 1^–1)) reduced thegrowth rates of both species. 100 ppm cadmium was lethal toD. tertiolecta but not to P. tricornutum. Lead (1 –4 ppm)initially increased the growth rate of D. tertiolecta but thencaused all but the 1 ppm culture to die. Lead (1–4 ppm)caused a decrease in growth rate of P. tricornutum. After exposureto 1 ppm cadmium, cultures of D. tertiolecta showed an increasedtolerance to levels of cadmium, and a changed response to levelsof lead. Exposure of P. tricornutum to either cadmium or lead,or exposure of D. tertiolecta to lead caused no change in responseto either metal.     

有机酸对Pb、Cd的土壤化学行为和植株效应的影响

有机酸对Pb、Cd的络合作用将其对土壤吸附Pb、Cd的影响和植株效应差异的研究表明,柠檬酸、草酸与Pb、Cd络合能力的大小与重金属本身的性质有关,络合作用影响土壤对Pb、Cd的吸附量,柠檬酸降低土壤对Pb、Cd的吸附,草酸则增加土壤对Pb、Cd的吸附.水培试验表明,柠檬酸可减轻Pb对小麦、水稻幼苗的毒害.柠檬酸对Cd的植株外观毒性效应影响不显著,但能促使植株茎叶、根中Cd含量下降.Pb和Cd复合处理条件下,Cd存在促使水稻植株对Pb吸收量增加,Pb存在抑制水稻植株对Cd的吸收.     

有机酸对Pd 、Cd的土壤化学行为和植株效应的影响

有机酸对Pd,Cd的络合作用将其对土壤吸附Pd,Cd的影响和植株效应差异的研究表明,柠檬酸,草酸与Pd,Cd络合能力的大小与重金属本身的性质有关,络合作用影响土壤对Pd,Cd的吸附量,柠檬酸降低土壤对Pd,Cd的吸附,草酸则增加土壤对Pd,Cd的吸附,水培试验表明,柠檬酸可减轻Pb对小麦,水稻幼苗的毒害,柠檬酸对Cd的植株外观毒性效应影响不显著,但能促使植株茎叶,根中Cd含量下降,Pd和Cd复合处理条件下,Cd存在促使水稻植株对Pd吸收量增加,Pd存在抑制水稻植株对Cd的吸收。     

土壤和大气铅对玉米植株内铅积累的影响和贡献率

采用土壤添加Pb和叶面喷施Pb溶液的方式,分别研究了土壤Pb和大气Pb在玉米植株各器官中的积累规律和Pb污染浓度与籽粒Pb含量、叶片Pb含量与籽粒Pb含量的相关性,以及土壤Pb和大气Pb对玉米籽粒Pb的贡献率.结果表明:土壤添加Pb后,玉米各器官中Pb含量表现为根＞茎＞叶＞籽粒,且主要富集在根系中;叶面喷施Pb后,玉米各器官Pb含量大小顺序是叶片＞茎、根＞籽粒,且主要富集在叶片中;随着土壤和大气Pb浓度的增加,玉米各器官Pb含量均呈现不同程度的增加;玉米籽粒中的Pb含量与土壤和叶片Pb浓度呈显著正相关(P＜0.01);土壤施加Pb的毒性临界值为118.95 mg·kg-1;大气Pb对玉米籽粒的贡献率为53.7％,土壤Pb对玉米籽粒的贡献率为46.3％,说明大气Pb通过叶面传输是玉米籽粒吸收Pb的重要途径.     

Effects of stent stiffness on local haemodynamics with particular reference to wave reflections

The placement of a rigid stent within an elastic vessel produces wave reflection sites at the entrance to and exit from the stent. The net haemodynamic effects of these reflections depend critically on the degree of stiffness of the stent and on its length and position within the diseased vessel, variables that have been found to affect the clinical performance of a stent. Here these effects are examined analytically, using a segmented tube model. The results indicate that the presence of the stent within the larger diseased vessel has the effect of producing higher pressure at the vessel entrance than that at exit. This pressure difference, when superimposed on the underlying pressure distribution within the vessel, has the net effect of actually aiding rather than impeding the flow, but the extent of this depends on the length and position of the stent. A short stent placed near the entrance of the diseased vessel may be favoured clinically for producing the least perturbation in the underlying haemodynamics and thus reducing the chance of restenosis, while a long stent placed near the exit may be favoured for producing a positive pressure difference and thus aiding the flow.     

Effects of microplastics and biochar on soil cadmium availability and wheat plant performance

Biochar is a promising amendment to promote cadmium (Cd) sorption and fixation in agricultural soil, where microplastics are emerging contaminants in soil. Herein, a greenhouse pot experiment was conducted to elucidate the effects on Cd availability in a soil–plant system by biochar and fresh/aged microplastics application. The fresh microplastics led to an obvious increase in soil Cd availability and Cd uptake by wheat plant, while the aged microplastics increased the available Cd in soil but had no effect on Cd uptake by wheat plant, which was likely attributed to the blocking effect of the aged microplastics on Cd transportation from the soil to the wheat plant. Unexpectedly, biochar had increased Cd availability and Cd uptake. The increased soil soluble Cd was because of both decreased soil pH and elevated dissolved organic matter (DOM) content resulted by biochar addition. Also, the unchanged Cd adsorption of the soil was likely responsible for the increased tested soil Cd availability. In addition, the combined effects of a greater decrease in soil pH, an increase in soil DOM content, and a reduction in Cd adsorption after the addition of microplastics to biochar-amended soil resulted in a significant increase (ranging from 2.63% to 47.73%) in Cd availability compared to soil treated with biochar alone. Moreover, fresh microplastics inhibited wheat growth, and greater inhibition effect was observed for their aged ones. The biochar elevated the wheat biomass; however, the coexistence of microplastics and biochar decreased the wheat plant biomass compared with biochar alone, due to the negative influence of microplastics in plant growth.     

Employment of associative bacteria for the inoculation of barley plants cultivated in soil contaminated with lead and cadmium

In laboratory experiments, the rhizobacteria Azospirillum lipoferum 137, Arthrobacter mysorens 7, Agrobacterium radiobacter 10, and Flavobacterium sp. L30 were found to have a relatively high resistance to the toxic heavy metals lead and cadmium (except that strain L30 was found to be sensitive to Cd). When introduced by means of seed bacterization, the heavy metal-resistant strains actively colonized the rhizosphere of barley plants cultivated in uncontaminated and contaminated soils. In both pot and field experiments, seed bacterization improved the growth of barley plants and the uptake of nutrient elements from soil contaminated with Pb and Cd. The bacterization also prevented the accumulation of Pb and Cd in barley plants, thereby mitigating the toxic effect of these heavy metals on the plants.     

Bioaccumulation of mercury,arsenic, cadmium,and lead in plants grown on coal mine soil

Mercury (Hg), arsenic (As), cadmium (Cd), and lead (Pb) are the major toxic metals released by coal mining activities in the surrounding environment. These metals get accumulated in the soils. The plants grown on the contaminated soil uptake these toxic metals in their roots and aerial parts. This study monitored the bioaccumulation of Hg and other three toxic metals in coal mine soil. The pot study of Hg accumulation in Brassica juncea showed that the extent of Hg uptake by roots and shoots of the plants grown on was high in the mature plant and Hg content in root was higher than the shoot. In the soil of unreclaimed overburden (OB) dump, the toxic metal content was higher than that of reclaimed OB dump which posed high ecological risk in the soil of unreclaimed OB dump. Bioaccumulation coefficient (BAC) value showed that Hg was not accumulated in the leaves of Dalbergia sissoo L., Gmelina arborea, Peltaphorum inerme L., Cassia seamea L, and Acacia mangium L grown on coal mine soil.     

Life history traits as predictors of plant rarity, with particular reference to hemiparasiticOrobanchaceae

We made a comparison between life history and reproductive characteristics of a group of Dutch rare (30) and common (105) plant species, all dicotyledonous and insect-visited forbs. The traits life span, clonality, breeding system, seed production, seed dispersal, and soil seed bank longevity are considered. All trait values have been ranked according to their possible effect on the vulnerability of a species for extinction, where low values indicate a low risk and high values a high risk for a species. Rare and common plants differed significantly in four traits: seed production, breeding system, seed bank longevity and clonality. The discriminant analysis showed that 79% of the 135 species was correctly classified in the group they presently belong to. Especially species that are rare now but were much more common 50–100 years ago were classified as being common species, pointing at the detrimental effect of habitat loss these species encountered at which they have not yet been able to adapted to. The data set include eight hemiparasitic plant species (familyOrobanchaceae), of which six are endangered in The Netherlands and two more common. Both rare and common hemiparasites scored high traits values, indicating that they are vulnerable for extinction. The hemiparasites had several characteristics in common: they are all annuals or biennials that have no means of clonal reproduction. They all have non-clustered, zygomorphic flowers that produce nectar and have a precise pollen presentation and are mainly visited by (bumble) bees. Mean life span was significantly shorter in the eight hemiparasiticOrobanchaceae than in the non-hemiparasiticScrophulariaceae used for comparison (4 species). Overall, we concluded that hemiparasitic plants have a special combination of life history traits which makes them vulnerable for local and regional extinction.     

Effect of 24-epibrassinolide on the photosynthetic activity of radish plants under cadmium stress

The present study was conducted to study the effect of 24-epibrassinolide (EBL) on changes of plant growth, net photosynthetic rate, carbonic anhydrase (E.C. 4.2.1.1) and nitrate reductase (E.C.1.6.6.1) activities in the leaves of Raphanus sativus L. under the influence of cadmium (Cd) stress. Cd reduced plant growth, photosynthetic pigment levels, net photosynthetic rate and the activities of carbonic anhydrase and nitrate reductase. However seed application of EBL reduced the toxic effect of Cd on plant growth, pigment content, photosynthesis and enzyme activities. The studies clearly demonstrated the ameliorating effect of 24-epibrassinolide in mitigating the toxicity of Cd in plants.     

Effects of cadmium,lead, and sodium salts on nitrification in a mull soil

Summary Increasing amounts of Cd, Pb, and Na salts were added to a fresh mull soil and the NO₃ and NH₄ concentrations measured after 2–8 weeks of incubation. The highest amounts used (CdCl₂ 9–18 mol/g dry weight, CdAc₂ 9–22 mol/g, PbAc₂ 121 mol/g and NaAc 250 mol/g) significantly increased NO₃ accumulation. Lower concentrations had either no effect or caused a slight decrease. re]19730529     

The levels of metals in dock-yard sediments with particular reference to the contributions from ship-bottom paints

Levels of the metals copper, lead, tin and zinc have been determined in a range of shipbottom paints by atomic absorption spectrophotometry. Copper, lead and zinc have been similarly determined in concentrated nitric acid digests and 1M ammonium acetate extracts of sediments taken from enclosed dock-basins at Liverpool, Tilbury and Manchester.At each of the dock-yards concentrations of all the metals in nitric acid extracts were elevated in the vicinity of dry-docks. These elevations are believed to be due to the presence of residues from the ship-bottom paints. The amounts of copper and zinc, which are major components of antifoulant paints, in the ammonium acetate extracts correlate closely with the levels in the nitric acid digests; lead, which is found mainly in anticorrosive and primer paints, does not.Direct toxic effects of the metals to marine organisms are considered, but are not thought to be important in view of the large dilution and dispersed capacities usually available. The possibility of organisms developing genetic resistance to heavy metals in enclosed dock-basins is discussed. It is noted that many of the dock-yard organisms are components of the ship-fouling ecosystem, so that the premature exposure to the toxins of antifoulant paints may result in the development of toxin resistance of considerable economic importance.     

氯离子和乙二胺四乙酸对镉的植物有效性的影响

通过水培试验,向营养液中添加不同浓度的Cl^-或乙二胺四乙酸（EDTA）,研究了离子的配合作用对水稻及油菜吸收镉的影响.结果表明,随着营养液中Cl^-或EDTA浓度的增加,水稻和油菜地上部与根中镉的浓度降低.Cl^-浓度的增加抑制了水稻对镉的吸收,地上部与根部的镉含量分别从212.2和345.1 mg·kg^-1降低到34.1和209.1 mg·kg^-1.EDTA的添加抑制了水稻及油菜对镉的吸收,水稻地上部与根部的镉含量分别从212.2和345.2 mg·kg^-1降低到50.0和4.2 mg·kg^-1;油菜地上部与根部的镉含量分别从86.7和149.2 mg·kg^-1降低到22.2和12.3 mg·kg^-1.在营养液培养条件下,Cl^-或EDTA与镉的配合作用降低了植物对镉的吸收,与Cl^-相比,EDTA的抑制作用更明显.