摘要:

The weight of wormcasts thrown on to the surface of eight fields of differing agricultural history depends on the numbers ofAllolobophora longaUde andA. nocturnaEvans present and also on the mean size of the individuals of these two species. The weight of wormcasts produced per acre per annum on the different fields varied from 1 to 25 tons and it is calculated that from 4 to 36 tons of soil per acre per annum pass through the alimentary tracts of the total population of earthworms present. The percentage pore space of a soil containing a high population of wormcasting species is much greater than that of a field with a high population of worms which do not produce wormcasts. In two old pastures, the amount of coarse sand relative to silt and clay was found to increase appreciably with depth: this distribution is probably a result of the long‐continued activity of earthworm

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07344.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

In a field experiment, the disease rating of the roots of barley plants suffering from ‘take‐all’ was reduced by application of nitrogen, and by a combined dressing of phosphate and potash. This reduction is attributed to the fact that manuring enables the cereal plant to produce new crown roots more quickly thanOphiobolus graminiscan infect them. In an earlier pot‐culture experiment, operation of this disease‐escape mechanism was inadvertently reduced by inoculating plants at the crown, and by environmental conditions exceptionally favourable to infection (sand culture and relatively high temperatures in the glasshouse). Under these conditions, not only was root disease rating as high in the series receiving a full supply of nutrients (NPK) as in that receiving only one‐third the full amount, but it was reduced almost to one‐half in the series receiving one‐third nitrogen in the presence of full phosphate and potash (PK1/3N). It is concluded that an increase in nitrogen supply may increase the intrinsic susceptibility of individual roots to infection, at the same time as it promotes disease escape and increases yield of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07345.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

The action of the antibiotics present in deal sawdust on the growth on Czapek‐Dox agar of cellulose‐decomposing fungi has been examined.Stachybotrys atraandChaetomium indicumwere strongly inhibited by substances in cold‐water extracts, butC. globosumonly slightly so. The extracts also contained material which stimulated the growth ofC. globosumbut not that of the other two fungi. The formation of perithecia byC. indicumandC. globosumwas also stimulated by the extract. There was no marked inhibition or stimulation of the growth ofAspergillus terreus, A. fumigatus, or three species ofPenicilliumby the ext

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07346.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Over eighty compounds have been assayed for fungistatic activity.Fusarium graminearum, Penicillium digitatumandBotrytis alliiwere used as test organisms. The preliminary results suggest that fungistatic activity is associated with the tendency of the substituents to withdraw electrons from the double bond. Nitroethylenes and fumarates are, for example, fungistatic. Tetraiodoethylene has high activity but this can hardly be attributed solely to the withdrawal of electrons from the double bond by the iodine atoms.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07347.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

A series of derivatives of acetylene dicarboxylic, halogenofumaric and related acids have been prepared and their fungistatic activities assessed. The lower halogeno‐ and thiocyanofumarates and acetylene dicarboxylates are highly fungistatic. The mode of action of these compounds is discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07348.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

It is an implication of systemic infection by the aphis‐borne viruses that potato plants with large haulms should be specially vulnerable to infection, and this implication is supported by evidence in the field.Haulms are reduced in size by short days, low temperatures, under‐nutrition and varietal differences. Certain observations are adduced to show that these factors reduce vulnerability. It is suggested that the transference of the potato from the short days, infertile soils and primitive cultivation on the Andes to the long summer days and productive farming of Europe and North America enhanced its vulnerability to aphis‐borne virus diseases: the further effects of changes of temperature and manurial practices in the last century need elucid

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07349.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Experiments on the technique of insect transmission of the cacao virus 1A (swollen‐shoot) are described. This virus is unique in being transmitted by mealybugs (Coccoidea) and the experiments show that all stages ofPseudococcus njalensisLaing and ofFerrisia virgataCkll. are vectors. These insects become infective after feeding for less than 4 hr. on the infected plant and transmit after less than 3 hr. on the test plant. The virus is non‐persistent in the vector after 3 hr. test‐feeding. The vectors can collect virus from either leaf, green shoot, bark or pod; the young symptom‐bearing leaf is the best site for infection‐feeding and the cotyledon of the bean for tes

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07350.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Continuous and well‐marked changes in composition are demonstrated during the development of the cotton boll, and discussed in relation to changes in susceptibility to pests and diseases occurring over this period.Cotton buds and flowers, the main food of the earlier instars ofHeliothisandDiparopsis, and, at the beginning of the season, ofPlatyedra, represent the richest recorded source of nitrogen available to the larvae.The first 2 weeks of boll development, when most physiological shedding occurs, are characterized by extremely rapid growth, the dry weight of the ovules being approximately doubled every 2 days throughout this period.The developing ovules are richest in reducing sugars during the second and third weeks, when moisture‐content is also highest. Bolls of this age are attacked by the later instars ofHeliothisandDiparopsis, which are the stages at which the accumulation of larval fat is likely to be most active. MaleDysdercus, which can survive for prolonged periods on simple sugar solutions, show a marked preference for bolls of this age, which are punctured to a varying extent by other stages ofDysdercus, probably primarily as a source of water. This is also the stage at which attack byNematosporais most damaging; reducing sugars provide a highly suitable source of carbon for this fungus.The cellulose of the mature lint and the oil and protein of the ripe seed are mainly laid down after the boll reaches full size (at 4–5 weeks under local conditions), about half‐way through its maturation period, and are largely derived from materials entering the boll in the course of its subsequent development. Premature senescence, such as that associated withAlternariaattack, can thus affect yield even when defoliation does not occur until after most of the bolls have attained full size.The ripening seed, becoming steadily richer in oil and protein during the latter part of boll development, forms the main food ofPlatyedratowards the end of the season, a change of diet reported to induce the larval diapause. Ripe seed provides food which is essential for satisfactory nymphal development and probably also for oviposition inDysdercus; specific protein requirements are possibly involved.Examples of direct effects of environmental factors on the development and composition of the boll are described. Over the range of conditions experienced by the experimental material these effects were relativel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07351.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

The problem of whether a given amount of active ingredient is more effectively applied in concentrated or dilute form is discussed. Ifyis percentage mortality andx1andx2are respectively log‐concentration of active ingredient and log‐volume (or deposit) of insecticide applied,ymay be regarded as a uniform, continuous function ofx1andx2. The amount of active ingredient is constant, i.e.x1+x2=k, so thatdx/dx1=−dy/dx2=δy/δx1−δy/δx2Probit mortality,Y, can be substituted foryin (4). Thus, whether an active ingredient is better applied in concentrated or dilute form depends on the relative magnitudes of ∂y/∂x1and ∂y/∂x2, or of ∂Y/∂x1and ∂Y/∂x2. Equation (4) is true whenever an insecticide consists of an active ingredient in a diluent, whatever the dosage‐mortality relationship. Previous work is discussed in the light of (4) and its probit form, and it appears that the concentration at which an active ingredient is best applied can depend upon the nature and quantity of the active ingredient, and the method of application of the spray. There may be other facto*** The probit form of (4) is applied to the probit plane and confirmed experimentally. Flour beetles,Tribolium castaneumHerbst were sprayed with pyrethrins in Shell oil P 31, and it was found that ∂Y/∂x1>∂Y/∂x2, so that a given quantity of pyrethrins was more toxic in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07352.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Laboratory and field experiments were carried out during 1946 to determine the effects of D.D.T. and of benzene hexachloride (B.H.C.)* on honey‐bees and on several wild be species.Laboratory experiments show that B.H.C. is a powerful contact and stomach poison and results of field experiments with commercial preparations confirm its danger to the foraging bee population. A few minutes' contact with treated surfaces is sufficient to cause death and blossom may remain poisonous for at least 3 days after treatment.In the laboratory D.D.T. has a contact action at fairly high concentrations and as a stomach poison is rather more toxic than lead arsenate. In the field, commercial preparations on open blossom are apparently harmless to foraging bee

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07353.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY