摘要:

Observations have been made on the influence of humidity on spore germination, the rate of elongation of the germ tubes and the production of asexual and sexual fructifications of various mould fungi. The humidity range at which the different species developed is given. Some of the Mucorales and certain pathogenic moulds required high humidities (100‐93%) for their successful growth.Penicilliumspp. had a wider humidity range (100‐80%).Aspergillusspp. were able to grow under conditions of even more restricted moisture supply. Spores of members of theA. glaucusgroup, particularly, germinated and developed at humidities as low as 70‐64%. The reasons for variations in the humidity range of the different species are discussed. The influence of the supply of nutrients on spore germination and subsequent mould growth is consi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06395.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Tobacco necrosis viruses were found to be the cause of severe necrotic disease which occurred in forced tulips in three different nurseries. From 20 to 50% of some varieties, e.g. Alberio, Korneforus, Crater, Rose Copland and Krelage's Triumph were affected, whereas others growing under the same conditions remained apparently healthy. The characteristic symptoms of the disease are necrotic spots and streaks, which cause much stunting and twisting and soon kill small plants. The disease was reproduced by inoculating healthy tulips with tobacco necrosis viruses.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06396.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Aphids (Capitophorus fragariaeTheob.) allowed to feed for several days on a strawberry plant with severe crinkle transmitted two viruses. The isolation and properties of one (virus I) have already been described. The other (virus 3) was separated by transferring the aphids to fresh indicators after 24 hr.Virus 3 was transmitted by aphids which had been allowed to feed on an infected plant for 6 days or more and persisted in the vector for several days. There was some evidence that the virus has a latent period in the vector. The symptoms produced by virus 3 onFragaria vescaand Royal Sovereign strawberry are described.On Royal Sovereign, viruses 1 and 3 together produced symptoms of severe crinkle and viruses z and 3 together produced yellow‐edge. A form of severe crinkle is thus shown to be caused by a virus complex which can be resolved by means of the vector, and severe crinkle is shown to be etiologically distinct from mild crinkl

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06397.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

At fourteen sites where winter wheat was growing commercially, twelve of which were known or suspected to be deficient in manganese, a spray of manganese sulphate was applied late in the shooting stage of development, and the effect on yield of grain estimated. Samples of certain organs of unsprayed wheat plants were gathered on three occasions between tillering and ear emergence, and samples of weed leaves on the same occasions and after harvest; these samples were analysed spectrographically for manganese.The results indicate that analysis of the wheat plant can be used to forecast its response to a manganese sulphate spray, and the following tentative limiting values for manganese content are put forward, above which no increase in grain yield as a result of treatment may be expected:(a)during tillering, 34 p.p.m. manganese in dry matter of lower leaf blades;(b)just prior to ear emergence, 36 p.p.m. manganese in dry matter of stems. The highest correlation obtained between response and manganese content was that with the values for stem samples gathered just prior to ear emergence.Analysis of weed samples can only be expected to indicate gross differences in the manganese status of different sites.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06398.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Apparatus was designed for testing the frequency of flights of aphids under different conditions of temperature, relative humidity, light and pressure. Young aphids (1–4 days after metamorphosis) flew more often and showed less individual variability than older ones; with all ages activity increased for the first few hours under experimental conditions. Starving increased activity for the first 1–2 hr. Aphids used in experiments on a second day flew less frequently than controls which had remained on the plant the first day. AlateB. brassicaewere more active thanM. persicae: both species showed alternating periods of activity and quiescence.At light intensities between 100 and 1000 f.c. there was little difference in flight frequency, but below 100 f.c. activity declined rapidly and apparently ceased with darkness.Changes in relative humidity temporarily affected flight frequency, a change to a higher humidity retarding, a change to a lower increasing it. After adjusting to the change aphids flew readily at all humidities tested between 50 and 100% with temperatures below 80° F. (26.7°C.). The combination of high humidity and high temperature (90°F. = 32·2°C.) sometimes inhibited flight.Changes of pressure often increased activity temporarily and flight frequency was greater under fluctuating pressure than under constant pressure.It is concluded that changes in microclimate in crops are adequate to influence frequency of flight of aphids and consequently the spread of virus

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06399.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

This paper considers the suitability of north‐east Yorkshire as a centre for the production of high‐grade seed potatoes, taking the number of aphid vectors of virus diseases as the criterion. Counts of aphids were made during three consecutive seasons on selected fields on the higher land in this area. These counts are related to the various geographical, climatic and biological factors found in each field and conclusions are drawn as to the most suitable districts within the area and the type of field which is likely to prove most satisfactory for this c

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06400.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Insecticidal smoke generators were tested in the laboratory and in practice. Each generator contained 110–120 g. of crude insecticide, either D.D.T. or benzene hexachloride. Over half the insecticide was evolved unchanged as a smoke of particles less than 1 μ in diameter, by a slow combustion mixture. In the laboratory tests, the generators were used at the rate of one to 1800–2500 cu.ft. (50–70 cu.m.). Benzene hexachloride had a greater initial insecticidal effect and a better residual action up to a week after treatment; thereafter (1 and 6 months) the D.D.T. was more effective. The residual effects of horizontal surfaces were good against bedbugs, but the deposits on vertical surfaces were not highly efficient. Residual action against mosquitoes of vertical surfaces a week after treatment was fair, but effects of inverted surfaces were poor.The deposits of active insecticide on horizontal surfaces were about 15–30 mg./sq.ft.; on vertical surfaces, 3–10 mg./sq.ft.; and on inverted surfaces, 2–6 mg./sq.ft.A field trial was conducted between August and November in kitchens infested by flies and cockroaches. The generators were used at the rate of one per 64 cu.ft. (18 cu.m.). A substantial reduction of flies for 11 weeks was obtained by D.D.T., but for only 2 weeks with benzene hexachloride. Both treatments reduced heavy cockroach infestations to negligible proportions for 2–3 months. There was evidence of some repellent effect.Thermal generators require careful precautions to prevent indirect tainting of food or beverages. They are very wasteful of insecticide especially since two or perhaps three treatments per season might be necessary. This would use twenty times as much insecticide as a spray treatment. On the other hand, labour and equipment costs are somewhat lower, and ease of operation very much greater, with sm

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06401.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

Methods devised for feeding individual insects with leaf areas bearing known deposits of insecticides are described, and the problems associated with incomplete consumption of the treated leaf portions are discussed. An account is given of the difficulties of applying the technique to small insects and to those with erratic feeding habits.Experimental data are given to illustrate the effects on insect resistance of the following: (i) rearing conditions, (ii) larval age and body weight, (iii) acute and chronic poisoning, (iv) the diluting effect of the leaf tissue consumed with the poison dose.The dosage mortality curve for stomach poisons was found to be typically sigmoid: analysis of results by the method of probits (Bliss, 1934) therefore proved satisfactory. Using lead arsenate against fifth‐instar larvae ofPhlogophera meticulosathe ratio of weight increase to increase in median lethal dose was found to be constan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06402.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

A method has been devised for observing the effects of a number of non‐volatile contact poisons on the oxygen uptake of groups ofOryzaephilus surinamensis.Toxic concentrations of D.D.T. and of its analogues applied as dusts toO. surinamensisincrease the rate of oxygen uptake: sublethal concentrations appear to have no effect. The total oxygen uptake of groups of starvingO. surinamensisappears to be constant, whether or not they are treated with D.D.T. or its analogues. In each case a linear relationship appears between length of life and total volume respired before death.The stimulus of D.D.T. toO. surinamensisis apparently quantal and the magnitude is independent of the concentration of D.D.T. in the dust. The stimuli resulting from the action of D.D.T. and its analogues are approximately equal, as are the rates at which the insects die. There is, however, apparently a correlation between molecular weight and length of life, i.e. there is a tendency for the insects treated with the poisons of lower molecular weight to die more rapidly than those treated with the analogues of high molecular weight.The effect of benzene hexachloride on the respiration ofO. surinamensishas been shown to be similar to that of D.D.T.The effects of a number of insecticides on the oxygen uptake ofO. surinamensishave been compared. As a result the insecticides have been classified in two groups:(a)those stimulating respiration, e.g. D.D.T., B.H.C., pyrethrins;(b)those depressing respiration, e.g. rotenone, Lethane B 7

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06403.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY

摘要:

An analysis of the frequency distribution of local lesions, produced by viruses on half‐leaves of a number of plants, shows that their standard error increases with increasing mean. Hence analysis of variance and statistical tests of significance should not be applied to lesion numbers unless they are suitably transformed. The transformation into logarithms over‐corrects so that the standard error decreases with increasing mean. A satisfactory transformation isy= log10(x+c), wherexis the number of lesions andcis a constant. A method is given of assessingcfor different experiments. Great accuracy is not needed; in an experiment discussed in detail a satisfactory transformation is obtained with any value forcbetween 15 and 80.On individual plants the numbers of lesions formed on half‐leaves are distributed more or less normally, whereas their distribution about the common mean for many plants is skew and ‘leptokurtic’. The distribution of the transformed numbers is almost normal, both for individual plants and about the common mean for a number

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1949.tb06404.x

出版商:Blackwell Publishing Ltd    

年代:1949

数据来源: WILEY