摘要:

SUMMARYIn a previous investigation it was shown that the periodic application of ammonium sulphete to closely cut turf could bring about a reduction in the weeds (plants other than members of the Gramineae)without producing significant changes in the soilreaction. Evidence is produced in this investigation that such reduction is due to the direct action of the ammonium ion.A number of small plots were laid out on a uniform piece of turf and treated, respective1 y, with ammonium dihydrogen phosphate, sodium nitrate, urea, dilute sulphuric acid, and ferrous sulphate alone and in combination with ammonium sulphate. The rate of application of the nitrogenous fertilisers was the equivalenk of the nitrogen in 3 Ib. ammonium sulphate per 1000 sq. ft. (1.2 cwt. per acre). Ferrous sulphate (FeSO,. 7 q O) was applied at 4 Ib. per 1006 sq. ft. and sulphuric acid at the equivalent of the sulphate radicle in the ammonium sulphate. The dressings were made weekly fiom May to September and the applications were “wateredin,” in order to prevent damage by solutions of high osmotic concentrationBy botanical analyses made initially and afterwards at monthly intervals the changes in the percentage area covered by each species were followed. It was found that a statistically significant reduction in the “total weeds,”i.e.thesum ofthe areas covered by all the different weeds, was brought about ody by the ammonium compounds. Although urea and sodium nitrate did not produce changes significantly different from the control, the slight increase brought about by urea was significantly different from. the decrease with sodium nitrate.The weeds in the sward varied in their behaviow to ammonium compounck. The majority of species, such asAchillea Millefolium, were reduced. On the other hand,Cermtium vulgareincreased significantly, but the additionofferrous sulphate inhibited this increase.All the nitrogenous treatments produced the same changes in the grasses, thePoaspp. increasing at the partial expense ofFmtuca ovim.With the remaining treatments the grasses did not change.Determinations of the pH of the soil were made at the beginning and endofthe experiment. The figures showed that owing to the high chalk content there were no significant changes apart from a small increase of alkalinity caused by the sodium nitrate.Since the ammonium compounds have alone produced significant weed diminutions, it seems evident that such reductions must be ascribed to a toxic action of the aqunonium ion. There is evidence from the results of earlier workers that the absorbed ammonium ions combine with carbohydrates or with organic acids. The suggestion is therefore put forward that the differences in the response to ammonium salts of the plants of the turf may be related to differences in the content of such substances. In this view the plants resistant to the injurious action of the ammonium ions, i.e. the grasses and a few of the weeds, should show a high content of available carbohydrate or of organic acid or both. The susceptible planks‐the majority of the weeds– the other hand should show a

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04335.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARY1This paper deals with a series of experiments carried out in Northern Ireland over a period of three years in order to determine the value of various seed treatments for controlling smuts and for use as general seed disinfectants in connection with the cultivation of the oat crop.2In so far as the control of oat smuts is concerned and at the concentrations used in these experiments, copper sulphate and copper carbonate proved to be of some value but caused definite injury to the crop, while sulphur and gypsum proved to have no fungicidal value. Formaldehyde gave complete control in nearly every case, the sprinkle method being considered more satisfactory than steeping, as it is more easily carried out and as the results obtained indicate that in some cases steeping may cause crop injury. The organic mercurial–“Ceresan”– gave almost as good results as formaldehyde.3As general seed disinfectants the organic mercurials–“Ceresan” and “Abavit B”–proved to be more satisfactory than formaldehyde, the average increase in grain yield from these plots being approximately 30 per cent, above the yield from the formaldehyde plots which in turn showed a yield increase of 16 per cent above the controls.4It is suggested that the greater efficiency of organic mercurials is due to the fact that the fungicide is retained by the grain at the time of sowing and remains operative during the early stages of crop development without causing injury to the plants.The fact that oat grain has been treated with “Ceresan” and “Abavit B” at varying intervals before sowing with complete success indicates that this method of treatment possesses a distinct advantage over the formaldehyde method where, in order to preclude possibly injury during germination, it is necessary to carry out the treatment immediately prior to sowing. No causes of poisoning as a result of the use of organic mercurials have occurred so far and it is possible that by taking reasonable precaution the. use of these compounds for seed dress

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04336.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

IV SUMMARY1A brief review is given of diseases affecting the underground parts of Narcissus plants, with especial reference t o the bulb rot associated with F.bulbigenumCke. and Mass., the symptoms of which are described both in stored bulbs and in the field.2In isolations made from stored bulbsP. bulbigenumwas found most frequently. Two strains of this organism are briefly described. Two other organisms of frequent occurrence in Narcissus bulbs, F.moniliformeandCylindrocarpon radidicok, are also described.3Inoculations into healthy bulb tissues with strains ofF. bulbigenurnwere found to produce the typical symptoms of the storage rot, and the fungus was reisolated without difficulty. In general, wounding of the tissue was necessary for infection to take place. In a few cases where infection was obtained without artificial wounding, naturally produced wounds are suspected. Inoculations of roots failed to produce the disease.Inoculatioas withF. moniliformeandCylindrocarpon radicicola, which are frequently found on diseased bulbs, failed to give infection, and it is concluded thatF. bulbigeniumis the causal agent of the bulb rot.4There is considerable variation in the resistance of different varieties to the fungus.5F. bulbigenurnwas occasionally found entering&athe nose of the bulb, but usually it attacked from the base upwards. A very frequent point of attack was at the junction of the two components of a doublenosed bulb. So far no clear evidence was obtained of the fungus entering the base of the bulb from infected soil through the dying‐back roots, as stated by Weiss to be the case in America.6High temperature and high humidity during storage were found to aggravate the disease in an infected stock, but in healthy stocks these same factors did not harm the bulbsorreproduce the disease.7The beneficial effect claimed for early planting of stocks as a means of checking the disease has not been substantiated. In the light of the figures obtained, the question must be considered to be open.8Support was found for the view put forward by Weiss that the disease may be spread during the hot‐water treatment against eelworm.9The surface sterilisation of bulbs with fungicides appears to offer promise as a method for reducing the amount ofrottingduring storage. Experiments are described in whichtestswere made of the effect of various concentrations of fungicides on the health of the bulbs themselves and on the germination ofF. bulbigenumspores.This investigation was carried out in the Department of Plant Pathology, Imperial College of Science and Technology, South Kensington, and a t the Biological field Station of the. College a t Slough, Bucks. In addition t o acknowledgments made in the text, thanks are due to Prof. Munro, Director of the Field Station, for the facilities afforded there; to DrG.H. Pethybridge and Mr W. C. Moore, of the Plant Pathological Laboratory, Harpenden, for much assistance in the way of material and references to literature; to Messrs G. R. Ban and H. R. Barr for many facilities for study at their Taplow Xursery and Covent Garden Warehouse; to Messrs the Proprietors of Hay's Wharf for cold‐store accommodation, and finally to Prof. W. Brown for his continual interest and assistance throughout all stages of the investig

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04337.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARYThe presence ofActinomyceswithin cacao beans is discussed, and descriptions by Waksman of three strains of a new species–Act. cacaoi– are gi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04338.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARY1Three further cases of the occurrence of the chlorotic disease of the hop, hitherto known from only one hop‐yard (of the Fuggle variety) in Worcestershire, are recorded from hop‐yards in the same county on the varieties Fuggle, Early Bird and Tutsham.2The chlorotic disease has been transmitted by grafting to the commercial varieties Tutsham,. Cobbs and Mathon. With one doubtful exception, all the affected plants showed as well the symptoms of mosaic disease.3The chlorotic disease has been transferred by grafting to three new seedling varieties (M. 45, p. 13 and GG. 45).4In three instances, individuals of symptomless mosaic carriers (of two varieties), to which chlorotic disease had been transmitted by grafting or budding, exhibited eventually marked symptoms of mosaic disease.5Two further cases are recorded of the appearance in scions of chlorotic symptoms in the same year in which the scions were grafted on the infected sto

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04339.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARY1Under a scheme, begun in 1927, and supported by a special grant from the Ministry of Agriculture since 1928, an attempt is being made to test the value of certain localities in North Wales for the production of seed potatoes.2Evidence is produced to show that out of fifteen farms originally selected for this purpose, eight have maintained their stocks without increase of virus diseases, three have shown only a slight increase, whilst four have been discarded from the scheme. Replicated yield trials at the College Farm proved that seed mixed from these eleven farms was equal to Scotch “stock” seed, and the value of this Welsh seed was confirmed by trials in a number of Welsh counties in which it was tested against ordinary T.S. Scotch seed.3Concurrently with this, a study has been made of the aphid population on the potato crops at these centres, which has led to the following conclusions:a.The absence of increase of virus diseases, and of leaf‐roll in particular, at the more successful centres is not due to the scarcity of aphides, nor to the absence of known vectors of the diseases, such asMyzus persicae.Neither can it be attributed to the non‐infective condition of the aphid vectors present at these centres since representative samples, taken from potato crops, transmitted leaf‐roll to healthy plants under glass. With one exception no transmission occurred with any of the species of aphides when taken from apparently healthy plants in a partially diseased crop. In samples taken from leaf‐roll plants transmission only occurred when they includedMyzus persicae.b.The accumulated data suggest that the maintenance of health in potato stocks is influenced not merely by the relative abundance of aphides, but rather by the relation between the date of maximum infestation and the stage of maturity of the foliage. The more successful centres, each year, showed either a delayed maximum infestation and/or the foliage was cut down earlier than at the less successful centres. The relative movement of aphides within the crops at the different centres is certainly of importance, but this is conditioned by many factors which are still under in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04340.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARY1The source and general character of three new virus diseases occurring inHyoscyanzusare described under the names ofHyoscyamusvirus (Hy.) 11, 111 and IV. They have a host range of various solanaceous plants not including any variety of potato.2Hy. I1 and 111 are non‐flterable (through L 3) and are transmitted to and from all their hosts except tomato by tEe aphidMyzus persicae.Hy. I11 survives for a relatively short period as clarified juice. Hy. II and Hy. III have many characters in common and are probably closely related.3Hy. IV is a different type of Virus, flterable through an L 3 candle and no insect vector has yet been found for it.4Problems arising from consideration of the data so far accumulated are submitted and discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04341.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARYThe results of a microscopic study made of the colour transition shown by the fleece of the Suffolk from birth to maturity are given. It is demonstrated that the physical structure of the fibre cuticle obviates the possibility of pigment inclusions.An explanation for the sporadic occurrence of coloured fibres in an otherwise white 3eece is attempted, and it is pointed out that, however else the pigmentary system of the Suffolk sheep may be stimulated, thresholds of irritation conditioned by temperature need not he considered as possible stimuli.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04342.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

SUMMARY1Two series of experiments were performed with a mixed culture of two species of soil bacteria with and without Colpidia, one series on a solution of peptone in soil extract, the other on a synthetic medium containing alanine.2An appreciable reduction in bacterial numbers was found on both media to occur in theColpidiumcultures as compared with the controls.3On the peptone medium theColpidiumcultures produced slightly more ammonia than the controls, in spite of their lower numbers of bacteria.4On the alanine medium theColpidiumcultures produced nearly the same amount of carbon dioxide and of ammonia as the controls.5In both series of experiments an inverse linear relation was found to exist between bacterial numbers and efficiency of ammonia production, and the same was found for carbon dioxide production in the second series.6The regression coefficients of efficiency on average bacterial numbers are significantly different in theColpidiumand control cultures fo the second series.7It follows that the stimulating effect of the presence of Colpidia is not due solely to the reduction of bacterial numbers to an optimum value, and it is suggested that in the cultures in which Colpidia are present, the bacteria are kept in a state of youth for a longer period.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04343.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY

摘要:

A Text‐book of Practical Entomology. By FrankBalfour‐Bro

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1932.tb04344.x

出版商:Blackwell Publishing Ltd    

年代:1932

数据来源: WILEY