摘要:

Summary.For the foregoing investigation of the relation between the virus of streak disease and, on the one hand, the insect‐vector,Balclutha mbilaNaude, and, on the other hand, the maize plant, a special technique was developed in which the inserts were manipulated and studied individually.The eggs laid by infective leafhoppers of this species produced un‐infective progeny, but the young leafhoppers might in any stage of development become infective after feeding upon a diseased maize plant. This infective power was retained during the change of skin. Experiments showed that adults might acquire the power of infection after feeding for one hour, but in lower proportion than was the case when the feeding period was of several days' duration. But even when the feeding period on a diseased plant extended through the whole course of development of the insect from the first instar to the adult stage, a proportion of the hoppers remained uninfective. Experimental study of these uninfective individuals led to the conclusion that no further periods of feeding on a diseased plant mould make them infective. Nevertheless, the progeny of such resistant females might become infective.A study of the infections produced by individual hoppers, when repeatedly transferred to fresh maize plants after short time intervals, gave no indication of a cycle of alternating infective and uninfective periods in the insect. The frequency of infection was increased by high temperatures, but was not influenced by preliminary starving of the hoppers.The power of infection was usually retained through the life of the hopper, but one definite exception was observed.Experiments showed that there occurred an incubation period of the virus in the insect, of variable duration but shortest at the higher temperatures. The minimum period observed was 6–12 hours at 30°C.Comparative studies of infection by single hoppers and groups of hoppers showed that the groups caused iufections more frequently and, on the average, in less time, but not more quickly than the quickest of the individuals feeding alone.With regard to the state of the plant at the time of infection, it was found that the frequency of infection and the incubation period of the disease in the plant were affected by the temperature and the age of the plant, but apparently not by soil moisture. Infection occurred as frequently when the hoppers fed upon the upper or lower surface of the leaf and on the young or old leaves, although infection through a young leaf might came the first symptoms to appear in an unusually short period.The passage of the virus down a leaf inoculated near its tip was not affected by certain forms of leaf mutilation. This downward movement occurred at a rate exceeding 40 cm. in two hours.From the diseased plant the virus was usually obtained by the leafhopper after feeding on the chlorotic areas but not from the green areas, except that a small proportion of hoppers usually became infective after feeding on the leaf through which infection took place, and similarly a small proportion (perhaps due to experimental error) after feeding on the green areas hang between the chlorotic areas in the fully disease

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07034.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.Rosette is a destructive disease of peanuts in South Africa, characterised by chlorosis of the young leaves and extreme stunting. Similar conditions in this plant have been reported from tropical Africa, Java and India.Experimental evidence is advanced to show thali rosette is not carried in the seed of the peanut nor in soil which has borne a diseased crop. It was successfully transmitted to healthy plants by grafting, but not by inoculation of juice from diseased plants.Insect transmission studies demonstrated the ability ofAphis leguminosaeTheo. to act as a vector of rosette. Thirteen species of leaf‐hoppers in a limited series of tests failed to transmit the disease.Aphis lguminosaewas shown to obtain the virus of rosette by feeding upon a diseased plant. Winged and wingless adults, when feeding singly, were shown occasionally to transmit the disease.An infrequently occurring mosaic‐like form of the disease is considered to be due to an exceptional reaction of individual plants to infection by the same virus as that causing typical rosette.In the field this disease is believed to overwinter in diseased plants, which germinate in the late autumn and survive the drought and frost of winter. Upon these plants the aphides may spend the winter. It is thought that in the spring winged aphides become disseminated from the overwintering plants and cause localised infections in the peanut fields. Later in the season epidemic spread of rosette frequently occurs. The evidence of six years of peanut‐growing indicates that spring infection of rosette is most severe in seasons following winters of exceptional rains.Rosette disease is likely to be largely escaped in the average season if the crop be planted at the earliest favourable date. Precautions recommended for control are the destruction of surviving plants during the winter and the removal of the diseased plants which develop in the new crop. The best prospect of practical control of rosette however is thought to lie in the discovery of resistant vari

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07035.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.1A disease of swedes is shown to be related to the presence of bacteria.2Certain features of the disease lead the authors to reserve their opinion as to whether bacteria are wholly responsible until opportunity for further investigation shall have presented itself.3An organism has been isolated and described.4The organism has been shown to be identical with one isolated contemporarily from cauliflower in France by Dufrenoy and Szymanek.5The identity of the organism withPseudomonas campestrishas been discussed and it has been suggested that it is probably a saltant strain of this species, though the authors reserve the question of actual identity until farther evidence is available.6The strain possesses more than one flagellum.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07036.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.1The insecticidal action of naphthalene and its duration in the soil have been studied.2When naphthalene is incorporated thoroughly with soil it shows a fairly potent toxic action on wireworms; uneven distribution lessens its efficiency as, owing to its low vapour pressure and consequent slow spread, it produces only a small zone of toxic action.3Naphthalene is slow in toxic action, taking three or four days to kill wireworms, as a consequence of which and of its repellent action to insects, if the chemical be unevenly distributed in the soil insects tend to move away from positions where toxic action would be exerted.4The persistence of the toxic action depends upon the soil type. In soils rich in organic matter, toxicity disappears more rapidly than in soils less rich in organic matter. Toxicity persists longer in sterile soils and in sand than in unsterilised soils, and in dry than in moist soils.5The rate of disappearance of naphthalene from soil has been determined. It depends very little upon volatilisation but almost entirely upon some factor inherent in the soil, which is more active in soils rich in organic matter than those poor in organic matter, and in unsterilised soils than in sterile soils.6Second and third doses of naphthalene added to the soil, when the first has disappeared, are decomposed more rapidly than the first dose.7The bacterial numbers of the soil are at first decreased by the addition of naphthalene, but there is a rapid rise during the period when acceleration in the rate of decomposition of the naphthalene is taking place. All the evidence indicates that the loss of naphthalene from the soil is mainly due to bacterial decomposition.8Experiments in sealed bottles indicate that the opening of the bottle and mixing of the sample expedite the disappearance of naphthalene from the soil.9The toxicity of α‐chlornaphthalene persists for a longer time in soils than naphthalene, and is decomposed at a slower rate. An admixture of naphthalene appears to induce a more rapid disappearance of the toxicity of the chlornaphthalene. α‐Chlornaphthalene is more toxic to plants than naphthalene.10Methods of estimating naphthalene are described. They depend on formation of naphthalene picrate. Picric acid can be more readily titrated by alkali in orange and yellow coloured light than in white light.11It was noted in several tests that the prolonged aeration of soils which had been heated and allowed to cool gave rise to formald

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07037.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.Naphthalene vapour having been shown by other investigators to be toxic to Red Spider,Tetranychus telariusL., it was thought that better control of the fumigation would be obtained if the substance was vaporised by means of a lamp. A suitable lamp was designed and is described herein. It has been used under commercial conditions and has given satisfactory results.Carnations and tomatoes have been fumigated with naphthalene and satisfactory control of Red Spider has been secured as shown by data given herein.Fumigations on a variety of glasshouse plants in addition to the foregoing have been conducted and general observations and recommendations on naphthalene fumigation for the control of Red Spider are included.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07038.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.The most reliable characters for distinguishing the larva ofAgriotes lineatusfrom the closely similar larva ofA. obscurushave been found in the spiracles. The spiracles ofA. lineatusare longer and more parallelsided than those ofA. obscurusand also bear a noticeably larger number of teeth bordering the orifices.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07039.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.1Sterile soil was inoculated with a known quantity of spores of four different fungi, incubated at 9°C. and at intervals representative samples were plated out by the dilution method and an analysis of the. plate population made. Results showed that high plate counts were not in any way connected with vegetative growth and supported Conn's idea that in such a case one is simply measuring the sporing capacity of the forms used.2Samples of moist soil and of soil which had been dried in a vacuum desiccator over calcium chloride were plated out by the dilution method and the number of fungal colonies per plate compared. A marked decrease was noted with the dried sample. The reduced pressure was found to have no effect as drying under ordinary air‐pressure gave comparable results.3Suspensions in soil, and in sand, of fragmented mycelia and of a mixture of fungal spores, were in turn plated out directly and after drying. No colonies developed from the sample in the desiccator containing only mycelia, whereas the sample containing spores was in no way affected. It is suggested therefore that the decrease obtained after drying is due to the desiccation of the vegetative mycelium in the soil and since the reduction in the number of colonies per plate is very pronounced after this treatment, it. is thought that the normal fungal constituents of the soil are present extensively in the mycelial condition.In conclusion I should like to acknowledge my indebtedness and gratitude to Sir John Russell for offering to me the hospitality of the Rothamsted Experimental Station and to Dr W. B. Brierley, Head of the Department of Mycology, for placing at my disposal all the facilities of the Department and for his encouragement and helpful eritieism during my work at the Stati

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07040.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Summary.1Experiments made to discover the death‐point of protozoa by phenol, carbon bisulphide and heat showed that phenol has a greater lethal effect than carbon bisulphide.2Heating the soil in a steamer for thirty minutes is usually sufficient to kill off the protozoa, and the treatment of glass‐house soil by steam destroys the majority of the protozoa and has a depressing effect on their numbers for a long per

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07041.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07042.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY

摘要:

Book reviewed in this article:Principles of Soil Microbiology. By SelmanA. WaksmanThe Microbiology of Cellulose, Hemicelluloses, Pectin and Gums. By A. C. Thaysen and H. J. BunkerStandard Methods of the Division of Laboratories and Research of the New York State Department of Health. By A. P. WadsworthSchädlingsbehämpfung. Grundlagen und Methoden in Pflanzenschutz. VonDrWaltherTrappmannAgricultural Parasitology. By C. L. Waltonand W. ReesWrig

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1928.tb07043.x

出版商:Blackwell Publishing Ltd    

年代:1928

数据来源: WILEY