摘要:

Changes in the seasonal activity of several species of earthworms have been followed in a permanent pasture field for 18 months, 1945–6. The two soil conditions which chiefly determine activity are temperature and moisture. Other factors are the occurrence of an obligatory diapause in the two speciesAllolobophora nocturnaandA. longa, and changes in population inA. chloroticaandLumbricus terrestris.Soil temperature and soil moisture also determined the weight of soil thrown up in the form of wormcasts during autumn, winter and spring. It is suggested that only two species,A. nocturnaandA. longa, are responsible for wormcasts and that the other four common species present play little or no part in this activity.At Rothamsted it was found that the previous agricultural history of the field is an important factor in determining the fauna. Old permanent pasture is characterized by a high percentage ofA. nocturnaand a rather lower percentage ofA. caliginosa.Ploughing old permanent pasture and reseeding to grass after 1 or 2 years arable reduces the proportions ofA. nocturnaandA. caliginosaand increases that ofEisenia rosea.Arable fields haveA. chloroticaas the dominant species and pasture fields 2–7 years grass after many years of arable fanning still show a high percentage ofA. chloroticaand a low proportion ofA. nocturna.A survey of the Carse of Stirling, Scotland, showed that soil type is also an important factor in determining the earthworm fauna.A. caliginosawas the dominant species on the three soil types studied, but the subdominant species varied. On clay soil,A. longawas subdominant; on loam,A. longaandL. rubellus; on sandy soil,A. longa, L. rubellusandA. chlorotica.The dominant species of pasture land at Rothamsted,A. nocturna, was not found at Stirl

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06367.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

This paper records the results of the experimental phase of an ecological study of the enchytraeid population of the sewage beds of the Huddersfield Corporation. The sewage in this drainage area is heavily charged with chemical wastes which have a marked effect on the fauna.Enchytraeus albidusHenle was the dominant worm whileLumbricillus lineatusMull., the common bacteria bed‐worm, was relatively scarce. The ability of these two worms to complete their life cycles in the sewage before and after treatment in particular beds was examined.The crude Huddersfield sewage proved toxic to bothE. albidusandL. lineatusbut the former was much more resistant. After treatment in the beds the degree of toxicity was much reduced and the final sewage was harmless to all stages ofE. albidusbut the eggs ofL. lineatuswere still unable to develop in it.The eggs of both species were less resistant to the toxic substances than the young worms; the adults were most resistant. High temperatures lowered toxicity by reducing the duration of the more susceptible early stages.There was no evidence of physiological adaptation ofL. lineatusto conditions in the Huddersfield beds. Wastes from both the main chemical works in the drainage area were examined and shown to be toxic; the domestic sewage was non‐toxic. Both the distillate and residue of one of the chemical wastes proved toxic, especially the latter.The toxicity could be entirely removed from the treated sewage by standing it over activated carbon for a few hours, or permitting slow oxidation for some weeks. The eggs ofL. lineatuswere used for these tests.The Huddersfield sewage was very acid from time to time and the acidity reached was sufficient to kill young worms and adults of both species. But this factor was not considered important in the beds owing to the persistent effects of the toxic sew

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06368.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

Benzene hexachloride containing 13% of the insecticidally active gamma isomer known as ‘Gammexane’ has been used successfully in a considerable number of field trials in the control of wireworm. On heavily infested land the effective dosage rates associated with an appreciable reduction in wireworm population, and giving a marked improvement in plant establishment and substantial increases in yield, range between 1 and 6 lb./acre (2–12 oz./acre of Gammexane), on oats and wheat. The effective dosage rates vary and depend upon whether the insecticide is combine‐drilled, broadcast, or applied as a seed dressing.Although D.D.T. applied by similar methods was associated with similar reductions in wireworm population, the use of this insecticide resulted in smaller yield in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06369.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

A direct‐spray technique for the biological assay of pyrethrins in Shell oil P31 is described, together with the experiments leading to its adoption. The technique is such that film effects are reduced to the minimum practicable, but it is otherwise as similar as possible to the film technique described by Parkin&Green (1943). Methods for statistical analysis of the results are discussed. For the biological assay of pyrethrins in Shell oil P31, the direct‐spray method is slightly superior to Parkin&Green's film method, but both techniques should have their uses in general experimental w

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06370.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

it is implicit in the concept of systemic disease that there should be a connexion between the size of the plant and the spread of infection.a first, general theorem, thought to be universally valid, is: the spread of an infectious systemic disease increases with the size of the plants, size being appropriately determined and other factors being constant.a second theorem for infections which enter a crop from without (e.g. from the soil or from another field) is: when a systemic disease enters a crop from some uniform outside source, the logarithm of the proportion of healthy plants is directly proportional to the size of the plants, other factors being constant; as an approximation, the proportion of infected plants is directly proportional to their size, provided that the proportion is small. a corollary to this theorem is that if the proportion of infected plants is small and if the size is inversely proportional to the density of planting, the number of infected plants per unit area will be approximately constant, factors other than size and number being constant.a third theorem for the spread of infection within a crop is: when a systemic disease spreads within a crop, the rate of infection is proportional to the size of the healthy plants, other factors being constant. if factors other than size, time and the proportion of infected plants are constant, the expression for the rate takes one of the three forms:dx/dt=ks(i‐x), (i)dx/dt=ks(i‐x)x, (ii)ordx/dt=ks(i‐x)f(s,t,x), (iii)in whichxand 1‐xare, respectively, the proportions of infected and healthy plants,sis the size, andkis a constant. the second part of this theorem is tentative.in these theorems we take by definition a disease to be systemic if a single effective transmission suffices to bring about maximum infection of the plant. size refers to that part of the plant which can receive infection. this definition, with the size of the receiving part having its colloquial meaning, serves for the first, general theorem. for quantitative relations, the guise but not the substance of the definition is changed: size is proportional to the probability that the plant receives infection at any instant from a uniform source in appropriate circumstances. both for general and quantitative relations there is a special case when disease is introducedintoa crop by insects or other vectors. size, then, is the catchment zone of the plant for the insects. this accords with the meaning assigned to size in other circumstances; size is here a convenient fiction, the use of which gives precisely the same results as the use of numbers, which are a reality.reduction of size is discussed as a measure of control peculiar to systemic d

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06371.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

As an introduction to this series of papers, a brief history is given of swollen‐shoot disease of cacao in the Gold Coast, and the nomenclature for cacao viruses is discussed.The symptoms of four virus diseases of cacao are described in detail, together with experimental data under the headings: cross‐immunity reactions, latent period, seed transmission, staining reaction, heat inactivation and rate of spr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06372.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

Experiments on cross‐immunity reactions between three viruses attackingTheobroma cacaoL. on the Gold Coast are described. A field trial involving 3 acres of graft‐inoculated trees revealed some degree of protection afforded byTheobromavirus 1B against infection with virus 1A. The protection appeared to be more effective against insect inoculation than against graft transmission, being only temporary in the latter. Virus 1C (probably unrelated but not to be calledTheobromavirus 2 until more evidence is available) conferred no protection against virus 1A.The latent periods for these viruses were calculated from this experiment, which also provided data on their effects on yield. Virus 1A reduced yield by 50% in the first year after inoculation and killed the trees in the second. Virus 1B had no appreciable effect on yield; virus 1C reduced yield by 50 % in the third year after inoculation but there was no further decline in the fourth.The rates of spread of these viruses were compared and significant differences demonstra

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06373.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

The symptoms caused by dandelion yellow mosaic virus on cultivated lettuce,Lactuca serriolaandL. virosa, are described and compared with those caused by lettuce mosaic virus. Lettuce is much more susceptible than dandelion to the yellow mosaic virus; no infections of dandelion were obtained by mechanical inoculation and only three by aphides, whereas infection of lettuce is regularly obtained by aphides and by inoculation provided an abrasive is used.Myzus ornatus, M. ascalonicusandAulacorthum solanitransmitted dandelion yellow mosaic virus but not lettuce mosaic virus, whereasMyzus persicaetransmitted the latter but not the former.Nasonovia ribicola, the common lettuce aphis, transmitted neither. Aphides became infective only after feeding periods of some hours on the diseased plants and ceased to be infective within an hour of the infective feeding. Their efficiency as vectors was not increased by a preliminary starving period, as happens withMyzus persicaeand lettuce mosaic virus. Lettuce mosaic virus was found in most samples of commercial seed, which explains its prevalence; no evidence was found for the seed‐transmission of dandelion mosaic virus and it is doubtful if it occurs, for infected lettuce are so severely affected that they rarely set seed.Cucumber mosaic virus was isolated from naturally infected lettuc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06374.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

The addition of a small quantity of a dust containing pentachloronitrobenzene to clamps of certain early and second‐early potato varieties has a marked effect in reducing the amount of sprouting which takes place over winter and in protecting the sprouts from damage by the fungusRhizoctonia Solani.A series of yield trials carried out over six seasons has shown that tubers which have been stored in clamps in presence of the dust give yields equal to those of chitted tubers.A dust containing a tetrachloronitrobenzene applied to potatoes kept in a closed space represses sprouting to a very pronounced degree. The possible use of this dust for conserving ware potatoes is suggeste

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06375.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

In an attempt to devise a practical method of killing wood‐destroying fungi, mycelia ofConiophora puteanaandMerulius lacrymanswere exposed to the beamed radiation from a standard Service radar transmitter transmitting pulses of radiation of wave‐length 9.1 cm. Growth ofConiophora puteanaon malt agar films on glass slides was checked. Many superficial hyphae were killed. Exposures up to I hr. did not kill the mycelium of either fungus when growing on malt agar slopes or plates, or wood blocks. The only obvious effect was a check in growth whenever drying of the mycelium occurred.It is concluded that the rays have no lethal effect and injure the fungi only through drying of the mycelium due to the increase in temperature which they bring ab

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06376.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY