bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experiments on the Spread of Potato Virus X Between Plants in Contact
Authors: Roberts F. M. 
Published: February 2008

Experiments on the spread of five strains of potato virus X were made with seven potato varieties and with tomato plants both under glass and in the field. Spread by leaf contact between healthy and infected plants was confirmed, and it was also found that spread could occur between plants whose only contact was below ground.The rate of spread was much greater in tomato than in potato plants, and virulent strains of the virus, which achieve a high concentration in infected plants, spread more rapidly than avirulent strains. In only one experiment with potatoes did more than 10% of the healthy potato plants exposed to infection become infected during one season. Datura stramonium and tomato plants became infected when growing in soil containing sap or residues from X‐infected plants.It was common in the field for potato plants whose foliage gave no reaction for virus X at the end of the season to yield a mixed progeny of healthy and infected tubers. Such infections are thought to result from underground spread.Attempts to transmit virus X from infected to healthy potatoes by means of Rhizoctonia solani failed. No examples of infection were found except when healthy plants came into direct contact with sources of the virus.
Resolution of Strawberry Virus Complexes
Authors: Prentice Ian W. 
Published: February 2008

Aphids (Capitophorus fragariae Theob.) allowed to feed for several days on a strawberry plant infected with yellow‐edge transmitted two virus fractions. The isolation and properties of one (virus 1) have been described previously. The other (virus 2) was separated by transferring the aphids to fresh indicators after 24 hr.Virus 2 was retransmitted after infection feeding periods of 24 hr. or more and persisted in the vector for several days. There is some evidence that it is itself a complex of viruses which can be separated further. On Fragaria vesca virus 2 produced chlorotic spotting, slight marginal chlorosis of the leaves and slight cupping of the leaflets. On Royal Sovereign strawberry it produced slight chlorosis of the young leaves.On Royal Sovereign viruses 1 and 2 together produced symptoms of yellow‐edge which is thus shown to be caused by a virus complex which can be resolved by means of the aphis vector.
Persistence of D.D.T. and Benzene Hexachloride in Soils
Authors: Smith M. S. 
Published: February 2008

Acid and alkaline soils, both alone and mixed with 2 % of D.D.T. or 2 % of benzene hexa‐chloride (mixed isomers, containing 10% of the γ‐isomer) have been exposed outdoors or subjected to controlled leaching in the laboratory. Residual insecticide has been estimated at intervals by a method involving dehydrohalogenation, and determinations have also been made of chloride content of soil, chloride leached and pH.Results showed that both D.D.T. and benzene hexachloride were very stable in the soils, about 95 % of the former and 80 % of the latter being recoverable after 18 months. Very little chloride was leached during this period. The residual insecticide exhibited marked toxicity towards woodlice.Eighteen months after treatment the benzene hexachloride soils prevented root growth of germinating seeds, while germination and early growth were normal in the D.D.T. soils. This harmful effect of the residual benzene hexachloride was still apparent when 1 part of the treated soil was mixed with 99 parts of the control soil (representing a concentration of less than 0–002 % of the γ‐isomer).
Nitrogen Content in Relation to Fungal Growth in Apples*
Authors: Colhoun John 
Published: February 2008

The effects of change in the concentrations of nitrogen, malic acid and sugar in a standard nutrient medium on the rate of spread of Cytosporina ludibunda Sacc. and Fusarium fructi‐genum Fr. have been studied.At low concentrations the rate of radial spread of Cytosporina ludibunda falls as nitrogen increases from about zero to 0.03 %, whereas at high acid concentrations the rate of spread increases with nitrogen increasing within the same range. At an intermediate concentration of acid spread is unaffected by varying nitrogen content. The response of Fusarium fructi‐genum to nitrogen is similar to that of Cytosporina ludibunda except that the acid content at which the reversal of the relationship between radial spread and nitrogen concentration occurs is lower than that for C. ludibunda.The presence of extracts from lentils or apples in media increases the rate of the radial spread of C. ludibunda and lowers the acid concentration at which there occurs a reversal from the direct relationship between radial spread and nitrogen content to an inverse relationship.
FACTORS AFFECTING THE ACTIVITY OF ALATAE OF THE APHIDS MYZUS PERSICAE (SULZER) AND BREVICORYNE BRASSICAE (L.)
Authors: BROADBENT L. 
Published: February 2008

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. Alate B. brassicae were more active than M. 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 diseases.
THE EFFECT OF INSECTICIDES ON THE RESPIRATION OF ORYZAEPHILUS SURINAMENSIS: AN ATTEMPT TO COMPARE THE SPEEDS OF ACTION OF A NUMBER OF D.D.T. ANALOGUES*
Authors: LORD K. A. 
Published: February 2008

A method has been devised for observing the effects of a number of non‐volatile contact poisons on the oxygen uptake of groups of Oryzaephilus surinamensis. Toxic concentrations of D.D.T. and of its analogues applied as dusts to O. surinamensis increase the rate of oxygen uptake: sublethal concentrations appear to have no effect. The total oxygen uptake of groups of starving O. surinamensis appears 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. to O. surinamensis is 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 of O. surinamensis has been shown to be similar to that of D.D.T.The effects of a number of insecticides on the oxygen uptake of O. surinamensis have 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 71.
THE ADJUSTMENT FOR A NATURAL RESPONSE RATE IN PROBIT ANALYSIS
Authors: FINNEY D. J. 
Published: February 2008

A revised scheme of computation is suggested for the fitting of a probit regression line to quantal response data which have to be adjusted because of the occurrence of natural responses not caused by the stimulus under test. The calculations lead to the same results as those proposed when the method was first introduced, but have the advantages of close similarity with multiple regression calculations and of simplifying the test of heterogeneity. The new scheme is illustrated on the example used in the earlier paper.A table of weighting coefficients for use with high natural response rates is presented.
STUDIES IN THE DIAGNOSIS OF MINERAL DEFICIENCY: VI. THE COMPOSITION OF WEED LEAVES IN RELATION TO POTASSIUM DEFICIENCY IN BARLEY
Authors: Goodall D. W. 
Published: February 2008

Leaves of five weed species (Brassica sinapis, Cirsium arvense, Polygonum aviculare, P. convolvulus and Potentilla reptans) from fertilizer trials on barley at four sites in Hampshire were analysed with a view to using their composition in forecasting the response of barley to fertilizers. The samples were gathered from as many of the 108 plots as possible, and were analysed spectrographically for calcium, iron, magnesium, manganese, potassium and sodium.Marked differences in composition between the five species were recorded, the most noteworthy being the high sodium content of Brassica sinapis and Cirsium arvense and the high manganese content of Potentilla reptans. There were also marked differences between the four sites, but these were not uniform as between the different species, and often failed to agree with those observed for barley.Superphosphate applications decreased the manganese content of the weeds in many cases, and increased their calcium content. Muriate of potash increased their potassium content, but tended to decrease that of magnesium and sodium. The only general effect of sulphate of ammonia on the composition of the weeds was a decrease in iron content.Except in Cirsium arvense, the potassium content of weed leaves was correlated with that of barley on the same plot if differences within a site only were considered. Differences between sites were not correlated in this way. The correlation between potassium content of weed leaves and the response of barley to muriate of potash application was worthy of note only in Polygonum convolvulus, and even in this case the correlation of site differences did not reach significance. It is tentatively suggested that increases in the grain yield of barley as a result of muriate of potash application are likely to occur only where the leaves of P. convolvulus contain less than 1.83% potassium.
A COMBINED HAND‐ OR POWER‐OPERATED SPRAYER FOR FLY AND MOSQUITO CONTROL
Authors: Higgins A. E. H. , Green A. A. 
Published: February 2008

A new sprayer is described which was designed in 1945 for the control of adult flies and mosquitoes with insecticides having a kerosene base. This sprayer has been shown in laboratory tests against houseflies, Musca domestica L., and yellow fever mosquitoes, Aedes aegypti L., to be highly efficient for both kill and knockdown and to achieve a particularly rapid knock‐down of mosquitoes.The sprayer can be operated with a hand pump or connected to a supply of compressed air. Air consumption is very low and when the sprayer is power‐operated, optimum biological efficiency is obtained at 20 lb./sq.in. air pressure. There is no spitting or dribbling from the nozzle and the mist does not settle so rapidly as to cause any appreciable staining of the floor. Although robust it is light, easily manipulated and can be dismantled into component parts for cleaning. It has no adjustments; but the nozzle, which must be machined with precision, is automatically set in its most effective spraying position when screwed home tightly.
THE INHIBITION OF HATCHING OF POTATO ROOT EELWORM (HETERODERA ROSTOCHIENSIS WOLL.) IN PARTIALLY STERILIZED SOIL
Authors: JOHNSON L. R. , TOWNSEND W. N. 
Published: February 2008

Experiments on the hatching of Heterodera rostochiensis have shown that the addition of ammonium carbonate to potato root water markedly inhibits hatching when the concentration of ammonia introduced is approximately 100 p.p.m. The strong acid salts of ammonia in equivalent amounts have no such inhibitory effect.These observations are linked with experiments on the effect of partial sterilization of soil on the hatching of H. rostochiensis, and it is demonstrated that delay of hatching in such soils is only effective so long as the ammonia concentration within the soil is maintained at a sufficiently high level.
RELATION BETWEEN PARTICLE SIZE AND SHAPE OF INSECTICIDAL SUSPENSIONS AND THEIR CONTACT TOXICITY: II. D.D.T. AND ROTENONE SUSPENSIONS AGAINST ORYZAEPHILUS SURINAMENSIS L., WITH SOME TIME‐MORTALITY STUDIES
Authors: MCINTOSH A. H. 
Published: February 2008

Methods already worked out for the preparation and testing of aqueous D.D.T. suspensions against Tribolium castaneum, by a dipping method, have been applied to Oryzaephilus surinamensis, giving similar results, i.e. toxicity increases with increase in particle size.In the same way, the precipitation of rotenone by exchange of solvents leads to the formation of simple aqueous suspensions. The theory of precipitation is described and methods are given of preparing five types of suspension: colloidal rotenone, a suspension of small elongated plates, a suspension containing small hexagonal plates in aggregates, and two suspensions containing hexagonal plate‐shaped crystals of different sizes.These were tested, by dipping, against Oryzaephilus surinamensis L. Within the range of crystal sizes up to about 150μ, toxicity is inversely related to the size of particle in suspension. The variation in median lethal concentration obtained in this way is of the order of 600 times. Crystal shape seems to be unimportant. Similar results were obtained with fine suspensions, using a spraying method.The variation of mortality with time was also studied, using D.D.T. against Tribolium castaneum and rotenone against Oryzaephilus surinamensis. In the former case, both colloidal and crystalline D.D.T. show progressively increasing kills with the passage of time. Crystalline rotenone behaves similarly, but colloidal rotenone gives an initial paralytic effect, followed by recovery of the insects.
VERNALIZATION OF WINTER RYE BY ULTRASONICS
Authors: SCHWABE W. W. , THORNLEY M. J. 
Published: February 2008

Petkus winter rye seed was subjected to ultrasonic vibrations of i Mcyc./sec. frequency in order to test the possibility of their having a vernalizing action. Seed which had not been soaked, fully imbibed seed, germinating seed (radicle showing) and seedlings with about 2 mm. long coleoptiles were treated with two intensities of ultrasonics for two periods of exposure.There is a slight favourable effect on germination rate of the unsoaked seed, but injury or death is caused by higher doses applied to the imbibed or germinated seed. Time to flowering was not affected by this treatment and no vernalization resulted.
THE EFFECT OF INSECTICIDES ON RESPIRATION
Authors: LORD K. A. 
Published: February 2008

A method is described by which non‐volatile contact insecticides may be applied as dusts in a modified Barcroft respirometer with the minimum of disturbance. The technique makes it possible to observe the initial effects of insecticides on insect respiration.This apparatus has been used to study the effects on the respiration of adult Tribolium castaneum Hbst. of a number of insecticides, including so‐called inert dusts, and other finely divided solids, some of which are used as diluents.At 80% R.H. neither talc, carborundum, Almicide (Al2O3), stockalite, nor decolorizing charcoal caused any appreciable immediate change in the rate of oxygen uptake of T. castaneum, but after 24 hr. the highly toxic substances, Almicide and charcoal, had caused a marked increase. At 20 % R.H. talc caused an increase in oxygen uptake only after 48 hr., but Almicide was shown to cause an almost immediate slight increase in respiration and a rapid evolution of water vapour. It is suggested that the increase in respiration may result from an increased metabolism to replace water lost through the cuticle.3:5‐Dinitro‐o‐cresol (D.N.C.), p‐nitrophenyl diethyl thionphosphate (E 605), γ‐isomer of benzene hexachloride (γ‐B.H.C), D.D.T., pyrethrins, toxaphene, chlordane, hexaethyl tetraphosphate all caused an increase in oxygen uptake before killing T. castaneum but lauryl thiocyanate did not. Toxaphene and chlordane required a much longer time to cause an increase in respiration than did any of the other subtances tested.D.N.C. in sublethal concentrations caused an increase in the rate of respiration of T. castaneum. Concentrations of D.N.C. giving 100% kill caused a rapid increase in oxygen uptake of which the magnitude and duration were independent of concentration.E 605 caused an increase in respiration after a time delay which was dependent upon the concentration used. The magnitude and duration of the increase in the rate of oxygen uptake were not greatly affected by the concentration of E 605.The effects of the concentration of y‐B.H.C. and the pyrethrins are complex and require further study. Both substances can affect T. castaneum without affecting respiration. Knock‐down can occur without affecting the respiration rate.
THE INSECTICIDAL ACTIVITY OF SUBSTANCES RELATED TO THE PYRETHRINS
Authors: ELLIOTT M. , NEEDHAM P. H. , POTTER C. 
Published: February 2008

The toxicity as contact insecticides of the esters of (±)‐3‐methyl‐2‐allyl‐cycfopent‐3‐en‐4‐ol‐i‐one with the natural (+)‐trans and with synthetic (±)‐cis‐trans‐chrysaii‐themum monocarboxylic acids has been compared with that of the natural pyrethrins. The comparison was carried out on five species of test‐insects.It was found that the figure for both the absolute and the relative toxicities of these compounds varied with the species used as test‐subject.The factors involved in this variation are discussed. The extremes of variation of relative toxicity for the compounds with the natural acid were from about one‐eighth as toxic as the pyrethrum standard when the aphid Macrosiphum solanifolii was used as test subject to nearly four times as toxic as the standard with the larvae of the moth Plutella maculipennis. The fully synthetic material varied from about one‐sixteenth as toxic as the standard to Macrosiphum solanifolii to nearly twice as toxic to the larvae of Plutella maculipennis. The compound with the natural acid was approximately twice as toxic as the fully synthetic material to three of the insect species, but the fully synthetic material was considerably more than half as toxic as the partially synthetic to the fourth test‐species. It is pointed out that while it is widely recognized that large differences in relative toxicity may occur when the effect of chemicals of widely different structure and mechanism of action are compared on a number of different test‐species, the fact that these differences may also occur with related chemicals with, presumably, a similar mechanism of action, has not been clearly stated.Even when the differences in relative toxicity are taken into account, the two synthetic pyrethrin‐like esters still show high insecticidal activity.It seems reasonable to suppose from the results that economic commercial synthesis of pyrethrin‐like insecticides is not impossible.
STUDIES OF THE CLOVE TREE
Authors: NUTMAN F. J. 
Published: February 2008

Extensive root disorganization is associated with all recognizable stages of the sudden‐death disease of cloves, the final symptoms being those of a rapid wilt. In the early stages of the disease, however, the water status of an affected plant is more favourable than that of a healthy one, in spite of the root disorganization. In the diseased plant, the transpiring power and assimilation rate of the leaves are greatly lowered, probably because of partial closing of the stomata. The consequent reduction in transpiration appears to account for the smaller water deficit found in the earlier stages of the disease.These results are considered to furnish additional evidence in favour of the hypothesis that the disease is caused by a pathogen.
THE DISTRIBUTION OF APHID INFESTATION IN RELATION TO LEAF AGE
Authors: KENNEDY J. S. , IBBOTSON A. , BOOTH C. O. 
Published: February 2008

The leaf‐by‐leaf distributions of free infestations of viviparous Myzus persicae (Sulz.) and Aphis fabae Scop, were recorded on sugar‐beet plants and spindle bushes in pots in the greenhouse, and the distributions of the various seasonal forms of A. fabae were recorded on the same plants growing naturally outdoors. The aphid distributions were related to the ages of the leaves estimated on an arbitrary scale of ten types of leaf distinguished by degree of unfurling and colour. The diverse types of distribution recorded were all reducible to a common general pattern: growing and senescing leaves were more susceptible to colonization than maturing, mature and dying leaves. The resultant two‐peaked curve of aphid density on a series of leaves at successive stages of development was found in its entirety on certain sugar‐beet plants, but part only of the complete curve was usually found, owing to the incomplete range of leaf ages present on any one plant, particularly on the spindle tree.Fundatrigeniae were found colonizing sugar beet, and spring and summer migrants were found starting colonies on the spindle tree. The normal association of each seasonal form of the aphid either with the ‘primary’ winter host, or with a ‘secondary’ summer host, but not with both, is therefore not obligatory. It is attributed to the normal inaccessibility of summer hosts to fundatrigeniae and the normal unsuitability of the winter host when the ‘alienicolae’ are migrating and its leaves are mature.When M. persicae and A. fabae were infesting the same plant at the same time, their distributions were broadly alike, but M. persicae extended on to both younger and older leaves than did A. fabae and more strictly avoided the more mature leaves. Hence it is suggested that the degree of adaptation of a given aphid to a given plant may be gauged by the extent to which the aphid can colonize the plant's leaves not only when they are growing and senescing but also when they are mature and fully functional.
THE DISTRIBUTION OF APHID INFESTATION IN RELATION TO LEAF AGE
Authors: IBBOTSON ALAN , KENNEDY J. S. 
Published: February 2008

Infestations of apterous Aphis fabae Scop, on potted sugar beets have been followed in detail for several weeks. The plants were somewhat stunted and their crowns presented an unusually complete series of leaf ages. Records were kept of the changing number and size of the leaves and of their stage of growth. Parallel records were kept of the changing population of aphids on every leaf, and the figures are analysed in various ways to show how suitability for the aphids varied through the life cycle of the leaves.The leaves were very suitable when young, became unsuitable as they matured, became suitable again just after maturity and then unsuitable again as they senesced. But among leaves at any given stage, those which were growing or senescing rapidly were more suitable than those changing slowly, unless the rate of senescence was very high. The differences of population density on different‐aged leaves were due largely to the preferences exercised by the apterous adults. The added effect of differences in the fecundity of these mothers while feeding on different leaves was not excluded, but could not be assessed. It is concluded that the physiological development of the plant as a whole determines, through the growth and senescence among its total complement of leaves, the progress and pattern of its aphid infestation.