摘要:

The geographical position and climatic conditions of the Gezira cotton area are briefly described. A description is given of the Blue Nile river, and Sennar Reservoir. The common water plants of die latter are listed. It is shown in the case of five of these plants that they tend to be divided in those that occur in shallow water and those that prefer deeper water. Details of the annual rise and fall of the water of the Reservoir are also given.The system of canalization in the Gezira is described and details given of the method of irrigation. A list is given of the common water plants in the Gezira canals, and their distribution over the canalized area is discussed. A comparison is made of the water flora of the canals of Egypt with those of the Gezira.A system of small experimental canals was used to study the life history of the more important water plants in the Gezira canals. Details are given of the extent of the spread of the plants in these canals during a period of 14 months. It was found that abundant growth and seed formation occurred when clear water was entering the canals, but that the bulk of the vegetative part of the plants tended to die when turbid flood water arrived. Abundant seed germination occurred during the turbid water period. Drying the canal bed for 3 1/2 months had little effect on the final quantity of weed developed in the canals when they were refilled. Seed remained viable after 3 1/2 months' dry exposure. Removal of the surface soil from the dry canal bed produced no significant control of the water plants when water again entered the canals. A short flush of water was allowed to flow down the dry canal bed. It was hoped that the seed would germinate and the seedlings be killed by exposure after the flush had ceased. The effect of this treatment on the subsequent plant growth was negligible.Laboratory experiments on the more important water plants showed that the vegetative part of the plants was killed after 8 days' dry exposure to the sun and that mercuric chloride, mercuric chloride‐iodide, and sodium arsenite in a concentration of 1/10,000 killed all plants after immersion in the poison solution for 5 days. At a concentration of 1/100,000 and immersion for 7 days none of these poisons was able to killPotamogeton nodosusPoir. Work on poisons was discontinued for reasons stated in the text.A short account is given of plants that invade the canals from the banks.The problem of water plant control is discussed, and it is shown that the most hopeful method of control would be a system whereby all infested canals are cleared at regular intervals designed to prevent seeding during the clear‐water period and to remove seedlings during the flood‐water period. The application of this method in the Hag Abdulla Subdivision is described. The successful control that resulted reduced the weeding costs by

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06752.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The nature of the competition between barley and certain annual weeds which are dominant at Woburn, under conditions where the available root space as well as the water, light, and nitrogen required by the plants are limited, has been studied. The weeds involved areSpergula arvensisLinn. (spurrey) andMatricaria inodoraLinn, (scentless mayweed).Where there is a limited and fixed root space, and where the amount of available nitrogen is also limited, and where barley or each of the two weeds are grown by themselves, there is a tendency for the yield of the crop or of the weeds to reach a maximum with a definite density of plants per volume of soil. When an excess of nitrogenous fertilizer is added, a limit is reached with each of the weeds where extra nitrogen, added as manure, does not increase the growth but only raises the percentage of nitrogen in the plants as grown.Where there is a constant amount of weediness, with either of the two weeds studied, an increase in the density of barley plants diminishes the injurious effect of the weeds. The combined weight of barley and weeds is hardly ever as great as that of the barley grown in weed‐free soil. In a mixed crop, the weight of both weeds steadily decreases as the number of barley plants increases.Where there is a constant number of barley plants per unit area, the increase of either of the weeds does not much effect the yield of barley till the number of weed plants exceeds the number of barley plants. The presence of a strong, well‐grown crop of barley largely reduces the production of spurrey and, to a less extent, that of mayweed. With a constant density of barley and a variable density of weeds, the total weight of barley and weeds, taking the above‐ground portion only, is almost constant whatever be the number of weed plants. Where the mixed plants are grown under slight nitrogen stress, the barley secures the greater part of the nitrogen absorbed, obtaining over 75 % of the nitrogen in the combined crop, even when the number of weed plants is greater than the number of barley plants. This applies to both weeds.If excess of nitrogenous fertilizer (ammonium sulphate) is added to the mixed crop of barley and weeds, above that which will increase the crop, any reduction in the yield of barley must be due to competition for root space. At the highest level of nitrogen used (which, however, did not apparently reach the maximum that the barley could utilize for increased growth), the reduction in the yield of barley with excess of spurrey present was only 12%: with mayweed, a much stronger competitor, it amounted to 45%.There is no evidence that with either of the weeds there is any special relationship between barley and the weeds. The effect seems to be only one of competition for root space or for nitrogen when there is not an excess of the l

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06753.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Two trials are described, each of twenty‐five varieties tested during two seasons and the intervening winter storage period. Sets were produced from seed in the‐first season and planted to produce mature bulbs in the second. In the second seasons of both trials, the effects of time of planting of sets were also investigated as part of a factorial experiment. In the later trial the effects of set size were also tested. Data are presented of varietal differences in bolting, yield, earliness and of behaviour of the sets in storage. The effects of set size and of late planting on these characteristics are also recorded. Some practical recommendations are made: thus, among those tested, varieties were found which bolted little and gave high yields when grown from sets, but it is emphasized that names of varieties as listed in seedmen's catalogues may not be reliable. Efforts are being made to maintain and improve by selection the most satisfactory of these strains. Late planting of sets is not recommended, for, although bolting was effectively controlled by this means, the yields were much reduced. Plants grown from large sets tended to bolt more than those from small, as has been shown by earlier workers; while on the contrary the yields from large and small sets were on the average alike. Comparing different varieties, the highest gross yields of all were produced from the large sets of non‐bolting varieties; but for highest yields of bulbsfree from flower stalkssmall sets should be used and this is advisable for all varieties. During storage the large sets lost less percentage weight than the small but they sprouted much more, and this is considered the more serious defect. The storage data demonstrate an additional disadvantage of late planting, for this involves longer storage and both sprouting and weight losses increase rapidly during late s

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06754.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Flax seed containing up to 10% of moisture was disinfected with a proprietary dry fungicide containing tetramethylthiuram disulphide (Nomersan) at the rate of 12 oz./cwt. of seed, and stored for periods of up to 18 months, without its germination being impaired.Experiments were made with samples of seed the moisture content of which, before treatment, varied within the range of 5‐8‐13‐2% and which were kept in a commercial store after disinfection. Treatments were carried out with an 8% solution of a soluble organo‐mercurial (Ceresan U. 564) at the rates of 0‐67 and 0‐9 gal./cwt. applied by the short wet method, and with an organo‐mercurial powder (Ceresan UT. 1875 A) at the rate of 12 oz./cwt. applied by the fixation method using 0‐9 gal. of separated milk per cwt. The results obtained show that treatment by either method has the effect of lowering the percentage of viable seeds during subsequent storage and that the higher the moisture content of the seed before treatment the earlier this effect becomes apparent. It is suggested that seed to be treated by the short wet method on a commercial scale should be dried to contain about 5% of moisture, that not more than 0‐67 gal./cwt. of liquid be applied and that the seed should not be stored for longer than 3 months after treatment. Following upon these suggestions, 10‐ton lots of seed were treated commercially by the short wet method using a Kontramix machine and no ill effects on the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06755.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The chemical effect ofMarasmius peronatuson beech litter is described, with particular reference to the ecological relation between fungus and substrate. Beech leaves, some infected, and others uninfected by this fungus, were analysed and the results compared.Analysis shows that a vital process involving loss of carbon is at work, and that the fungus decomposes lignin, converting it into soluble products by the action of exoenzymes. It is suggested that by this process it is contributing to conditions favourable for beech regeneration.The fact that this fungus can more successfully colonize hardwood litter (e.g. beech) than other types of substrate, is explained by consideration of its physiology.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06756.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Isolations were made of mould species actively growing on a variety of feeding stuffs stored at fixed humidities between too and 65% for periods of up to 4 years. The factors influencing the species of moulds isolated were: (1) die relative humidity of the atmosphere; (2) the length of the storage period before the isolations were made; (3) the type and origin of die feeding stuffs from which the isolates were obtained.A critical humidify existed for each species below which the development of mould spores could not take place. At relative humidities (R.H.) between 100 and 90% a large variety of moulds were able to develop. Members of die Mucorales and the Fungi Imperfecti were not isolated below 90% R.H. and, although ***Pemicillium app. flourished between 100 and 85% R.H., they were not isolated below 75% R.H. ***Aspergilhes app., on the other hand, were able to develop under conditions of very restricted moisture supply. Some members of the A. ***glaucus group were able to grow at humidities as low as 65‐70%.In general, the moat commonly occurring moulds on the feeding stuffs used in these trials were small ***ascospored species of the A. ***glaucus group, particularly A. ***repens and A. ruber. It is considered that it is these species that will most frequently cause mould damage to feeding stuffs in commercial store

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06757.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Several strains ofPseudomonas mors‐prunorum(Wormald) andPs. prunicola(Wormald) isolated from pathological lesions of plum and cherry were studied together with the causal organism of bacterial canker of stone‐fruits in California(Ps. syringaefrom apricot) and other phytopathogenic bacteria obtained from pear and syringa. Comparison was also made with pseudomonas forms pathogenic to pea, bean, lettuce, and tobacco, and with the common saprophytesPs. fluorescens and Ps. pyocyaneus.With the exception of two yellow organisms(B. pruniand the Pear 8 strain—the latter, however, very occasionally showing fluorescence), all belong to the green‐fluorescent group ofPseudomonas(Dowson's Group II). On the basis of their dissimilation of C and N compounds a very close relationship has been established between these fruit‐tree and syringa pathogens of the green‐fluorescent group.Ps. mors‐prunorumis not highly specialized in its nutrient requirements but can satisfy its fundamental C and N requirements from a very large variety of simple substances. The only consistent biochemical differentiation shown byPs. mors‐prunorum(including some of the syringa strains) in comparison withPs. prunicola(includingPs. syringaefrom apricot and most of the pear strains) is its more rapid production of add from sucrose. Both themors‐prunorumandprunicolavarieties produce a levan from sucrose, which causes a raised gummy growth on solid sucrose‐containing media. This applies also toPs. pisi, Ps. tabaci, and Ps. phaseolicola, but is not the case with the weakly pathogenic forms—Ps. marginalis, cerasi (= trifoliorum, from bean), and the saprophytes—Ps. fluorescens and Ps. pyocyaneus.On the basis of biochemical characteristics, considered apart from host pathogenicity, there is no justification for erecting to specific rank these various levan‐forming. green‐fluorescent, p

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06758.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Severe etch virus prevents die multiplication of potato virus Y andHyoscyamusvirus 3 and replaces them even in plants in which they are established. Mild etch virus reduces the concentration of potato virus Y but does not suppress it completely. Cucumber virus 1 multiplies normally in mixed infections with any of the three other insect‐transmitted viruses. Possible implications of these results on the mechanism of virus multiplication are discussed; it is suggested that these viruses inactivate in cell sap at approximately the same rate as they denature in vitro.No differences were found between the stability of antibodies to viruses with different propertie

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06759.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The present paper summarizes what is known about the economic importance and diet of the house sparrow. The species is widespread in the Old World, and in the last 100 years has more than doubled its original range through introductions, settling most abundantly in grain‐producing areas of the world. Owing to a prolonged breeding season, its productivity is high and one pair will fledge about eight young per annum. The consequent very high density of the population in many areas is a major factor in making the sparrow a grain pest. Movements, migratory or local, are not marked in British sparrow populations.A single sparrow eats about 6 1/2 lb. of food per year, and as this is only partly and seasonally grain, it is the great numbers of the bird which constitute the economic menace. Cases are recorded in which 25% of an acre of wheat was destroyed by sparrows and in Russia up to 30% of a crop is generally lost. Table 1 gives a summary of the information available in the literature from stomach analyses.Grain. Data are not very satisfactory for Britain, but in arable areas sparrows' food consists of 75‐80% of grain. A lot of this is waste corn and poultry feed (three‐quarters according to American figures), so that the limitation of such sources of food might form an important first step in controlling sparrows. In fruit‐growing, garden and suburban districts far less grain is eaten (17%). Nestlings eat very little grain: in arable areas it may be as much as 40%, but in non‐arable areas the diet is almost wholly animal. Data for other countries are more complete. Specimens examined from grain‐growing areas (America, Turkestan) show that corn generally comprises half or more of the diet. In America the figure is 78%, but three‐quarters of this is waste grain or feed. In Turkestan two authors give about 50% and one 13%. In the latter case, owing to its great density, the sparrow was still a major crop pest In park and suburban districts results are much like those from Britain: 30‐40% grain is about an average figure. The same differences apply to nestlings: they may exceptionally take up to 50% grain but usually insects predominate, especially during the days just after hatching (50‐78%).Weed seeds. These are not eaten by nestlings. In Britain 10% in arable, 20% in non‐arable arm are the figures given. The same percentage is given for America, but in Germany authors give 34%. and in Turkestan 46 and 83%. It is not certain that this part of the diet is entirely beneficial economically, since some of these seeds pass through the gut in a viable condition, so that the sparrow may be an agent for spreading weeds.Insect food. The proportion of this item in the sparrow's diet varies greatly with locality and season. In non‐arable areas 35% of the food may consist of insects, and this is taken mainly in the summer. In exceptional cases very large numbers of insects may be eaten. The food of nestlings consists mostly of insects in all localities, but in non‐arable areas practically all the food is animal. Most of the species of insects taken are harmful to agriculture.Damage to fruit buds, green vegetables and flowers may be of importance sporadically, but does not call for more than local action.Apart from this, urban sparrows do no great damage and are useful scavengers. It is not thought that big flocks of sparrows in die harvest fields have moved out of the towns temporarily. In competition with other species of birds the sparrow probably menaces only the house martin(Delichon urbica)seriously by appropriating its nest. The evidence examined, though badly needing amplification, especially for Britain, suggests that house sparrows need controlling in arable,

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06760.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Hatching experiments were carried out with cysts of the potato‐root eelworm. The effect of solutions of potato‐root excretion mixed with root excretions of six types of crucifer seedlings was studied. With cress, white mustard, and black mustard, the emergence of larvae in the mixed excretions was very much less than that from control cysts in potato‐root excretion alone. On subsequent return to potato‐root excretion alone, larval emergence was found to be unimpaired in the case of white and black mustards; in the case of cress, however, the total emergence differed significantly from control. Similar effects, of both types, were obtained with certain dilutions of ally isothiocyanate, the mustard oil of black mustard seed, in potato‐root

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06761.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY