bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations on the Development of the Cotton Boll, With Particular Reference to Changes in Susceptibility to Pests and Diseases
Authors: Rainey R. C. 
Published: February 2008

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 of Heliothis and Diparopsis, and, at the beginning of the season, of Platyedra, 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 of Heliothis and Diparopsis, which are the stages at which the accumulation of larval fat is likely to be most active. Male Dysdercus, 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 of Dysdercus, probably primarily as a source of water. This is also the stage at which attack by Nematospora is 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 with Alternaria attack, 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 of Platyedra towards 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 in Dysdercus; 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 relatively small.
The Phytotoxicity of D.D.T. and of Benzene Hexachloride
Authors: Stoker Rosemary I. 
Published: February 2008

Spraying with two preparations of D.D.T. had a negligible effect on the maturation of outdoor tomatoes and of summer cabbage. Spraying with a commercial D.D.T. suspension damaged cucurbits and treatment with the suspension base distorted glasshouse cucumbers during one season only.Benzene hexachloride (B.H.C.) sprays did not affect the yield or flavour of tomatoes, but, at concentrations higher than those normally used, they severely scorched radish, turnip, swede, kale, spinach and beetroot seedlings. The application of B.H.C. dusts stunted seedlings of radish.On one occasion young potato foliage was damaged by relatively high concentrations of two compounded B.H.C. sprays and by B.H.C. dust but late‐season older foliage was unaffected. A spray compounded from B.H.C. dispersible powder caused tainting of potatoes, peas, carrots, beetroot, marrows, cauliflowers and lettuce. Apples and plums treated with B.H.C. spray preparations developed a taint after cooking.
Problems in the Cultivation of Winter Lettuce
Authors: Brown By W. , Montgomery N. 
Published: February 2008

In a four‐year study of winter lettuce cultivation, attention has been given to the effects of variety, dates of sowing and transplanting, method of preparing seed‐beds, nature of field soil, and fungicidal treatments upon percentage survival and date of maturity of the cropThe inferiority of the variety Trocadero Improved to such a winter variety as Imperial is due mainly to its susceptibility to Pythium root rot. This disease often causes severe thinning of the stand of Trocadero seedlings and dwarfing of many of the survivorsLate autumn plantings of Imperial and other winter varieties survived better overwinter on a medium‐heavy loam than on a light sandy soil. The disparity varied in different seasons and was not associated with severity of winterThe dates of maturity of the crop in relation to dates of sowing and transplanting have been determined over the four‐year period. On the basis of these, and on the records of survival and of market prices, an estimate can be obtained of the financial aspects of different cultural methodsFungicidal treatment in the seed‐bed of plants set out in the field in November gave little improvement in survival; but pronounced benefit was obtained by February or March dusting of seedlings which had overwintered in the seed‐bedThe onset of disease in overwintering seed‐beds was found to be influenced by the nature of the soil and by the manner of preparation of the seed‐bedThe interrelations of overwintering and soil type are briefly discussed, with special reference to the effects of soil type (i) on the root system, and (ii) on microbiological interference with invasion of die stem by Botrytis
Studies on the Importance and Control of Potato Virus X
Authors: Bawden F. C. , Kassanis B. , Roberts F. M. 
Published: February 2008

The success of seed certification schemes in controlling the aphis‐transmitted viruses that cause leaf roll and rugose mosaic has greatly increased the relative importance of potato virus X, in spite of the value of such schemes in reducing the prevalence of the most virulent strains. Virus X occurs throughout commercial stocks of most varieties and is responsible for many of the uncertainties and difficulties encountered in field inspections, for the production of leaf symptoms by many strains depends on the weather. Also, the predominating virus strain in a stock may change from season to season.Methods of testing for the presence of avirulent strains in potatoes are described. These include transmission to suitable indicator plants, plant‐protection tests, and serological methods. The virus content of different parts of the plant varies widely, but is everywhere high enough for transmission to indicator plants at all times of the year. The virus content of immature tubers is too low to give a precipitin reaction, but extracts from developing sprouts contain nearly as much virus as those from foliage, and can be used reliably.Infection of virus‐free stocks of the varieties Majestic and Arran Banner with four different strains of virus X reduced their yields by amounts varying from 5 to 24%. Scotch Stock Seed Majestic, however, cropped better than the virus‐free seed, and the need for considering additional factors to freedom from viruses when selecting clonal lines for propagation is stressed.Virus X was not transmitted by cutting healthy tubers with a knife previously used to cut infected ones, and cut tubers whose storage parenchyma was rubbed with infective sap gave rise to virus‐free plants. Infection occurred when sprouts were rubbed with infective sap, and the virus also spread from infected to healthy sprouted tubers stored in the same sack.Spread of the virus under natural conditions is slow, and it is concluded that the maintenance of virus‐free stocks under commercial conditions is feasible, provided that precautions are taken to prevent contact with infected plants. The relative importance of volunteer plants and other sources of infection is discussed, and methods of testing the virus‐free stocks are suggested.
Studies on the Relationships Between Earthworms and Soil Fertility
Authors: Evans A. C. , Guild W. J. McL. 
Published: February 2008

The rate of cocoon production in British Lumbricidae differs considerably from species to species and is greatly affected by soil temperature, moisture and the food supply of the adult worms. Only two out of fourteen species studied frequently produced more than one worm per cocoon, and twins were only recorded once in many hundreds of observations on four species of the genus Lumbricus.The incubation period of the cocoons and the growth period to sexual maturity varies from species to species and also depends on the time of year at which the cocoons are deposited and the young worms emerge.
The Contact Toxicity of a Number of D.D.T. Analogues and of Four Isomers of Benzene Hexachloride to Macrosiphoniella San Born I and Oryzaephilus Surinamensis*
Authors: Lord K. A. 
Published: February 2008

Twenty‐three analogues of D.D.T. and four isomers of benzene hexachloride have been compared with D.D.T. for toxicity as contact insecticides using a direct spraying technique. Each substance has been tested against two insect species: Macrosiphoniella sanborni and Oryzaephilus surinamensis. The substances tested included a number of halogen and alkyloxy analogues of D.D.T. and a number of compounds of varying degrees of chlorination between diphenylethane and D.D.T.The biological data have been examined, as far as possible, by the method of probits.The probit lines for the D.D.T. analogues varied both in position and in slope: those for the isomers of benzene hexachloride in position but not in slope. In general, neither the relative positions nor the relative slopes of the probit lines for the various substances were the same against the two insect species.The toxicity of substances analogous to D.D.T. appears to be related to molecular weight, with maximum toxicity occurring in the molecular weight range 300–450.Among D.D.T. analogues the slope of the probit line is apparently correlated with molecular volume. The variation of the slope of the probit lines has been discussed, and it has been concluded that it arises from differences in the interaction of the poisons with the test‐subjects.The various theories relating to the toxicity of D.D.T. and B.H.C have been discussed in relation to the experimental data described here. To account for all the experimental results by means of one theory it is necessary to postulate a physico‐chemical mechanism of toxic action. Such a mechanism implies that the intensity of biological action will be dependent upon the physico‐chemical properties of the poisons, whether or not a specific molecular configuration is involved, and toxicity is therefore dependent on the molecule as a whole.
The Toxicity of Vapours to the Grain Weevil
Authors: Ferguson J. , Pirie H. 
Published: February 2008

The values for concentrations in air of the vapours of approximately one hundred different chemical substances required to produce 50% mortality in samples of the grain weevil Calandra granaria, have been determined. Relationships between chemical constitution of these substances and their toxicity to the grain weevil are discussed, using as a measure of toxicity the relative saturation of the vapour concentration producing 50 % kill. The relative saturation is equal to the thermodynamic activity of the vapour at the concentration in question.It is found that the substances used can be divided into two broad classes: (a) one class in which the toxic thermodynamic activities lie between o‐1 and 1 ‐o and (b) another in which the activities are much lower—down to 0–0004.The first class exhibits certain linear relationships between the logarithms of toxic concentration and saturated vapour pressure, which are not shown by the second class. The toxicity of the first class is ascribed to a physical mechanism, and is believed to be such that phase equilibrium relations play a predominant part in determining the value of the toxic concentration measured externally to the insect (Ferguson, 1939).The toxicities of members of the first class, as measured by their toxic thermodynamic activities, show the following relations with chemical constitution:

Toxicity in homologous series decreases steadily from the first member as the chain length increases, finally disappearing.
Halogen substitution in hydrocarbon skeletons has only a small effect on the ‘physical’ toxicity, increasing it slightly. There is practically no difference in the effect of different halogens.
Hydroxyl substitution markedly decreases ‘physical’ toxicity.
The substitution of—CO or —CHO groups markedly increases ‘physical’ toxicity. The aliphatic amines and the alkyl formates examined do not appear to act by a physical mechanism, nor do many of the alkyl bromides and iodides.
Observations on a Virus Disease of Certain Crucifers in Trinidad
Authors: Dale W. T. 
Published: February 2008

A virus disease ofBrassica juncea Coss., B. Mnensis L. and Raphanus sativus L. var.hortensis Backer occurs in Trinidad, but is not serious. Rape (Brassica napus L.), turnip(B. rapa L.) and Lepidium virginicum L. are susceptible, but cabbage, cauliflower, kohlrabi and the European radish seem to be immune. Zinnia elegans Jacq. and tobacco (Nicotiana tabacum L.) are also susceptible, but no infections were obtained on six other Nicotiana species, beetroot, Swiss chard and cowpea. Tobacco gives only necrotic local lesions, whereas the other hosts give no local lesions, but a systemic mottling, usually accompanied in crucifers by leaf deformation and stunting of the plant.The virus is transmitted by Rhopalosiphum pseudobrassicae (Davis), which is probably responsible for spread in the field. Its thermal inactivaticm‐point is 58d̀ C, dilution end‐point 1:1000, and longevity in vitro 4 days at 16–18d̀ C. and 3 days at 24–30d̀ C. The properties and host range of this virus are compared with those of others affecting the Cruciferae. It has affinities with some of them, but is considered to be distinct.
A TECHNIQUE FOR DETERMINING THE STOMACH POISON EFFECT OF INSECTICIDES USED AGAINST LEAF‐EATING INSECTS
Authors: WAY M. J. 
Published: February 2008

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 of Phlogophera meticulosa the ratio of weight increase to increase in median lethal dose was found to be constant.
THE TRANSFORMATION OF LOCAL LESION COUNTS FOR STATISTICAL ANALYSIS
Authors: KLECZKOWSKI A. 
Published: February 2008

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 is y= log10 (x+c), where x is the number of lesions and c is a constant. A method is given of assessing c for different experiments. Great accuracy is not needed; in an experiment discussed in detail a satisfactory transformation is obtained with any value for c between 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 of plants.
STUDIES OF WIREWORM POPULATION III. SOME EFFECTS OF CULTIVATION
Authors: SALT GEORGE , HOLLICK F. S. J. 
Published: February 2008

The number of wireworms in successive collections from five Cambridgeshire fields declined during the first year of cultivation to 25 % of the number present before the fields were ploughed from old grass. The decline in numbers was accompanied by a change in the composition of the wireworm population; the marked inverse correlation between number and size of larvae, which held for the wireworm populations under grass, progressively altered towards uniform numbers of the different size‐groups. The incidence of natural control on the different sizes of larvae was obscured by their growth, and more medium‐sized and large larvae were lost than would appear from the population‐size histograms.Three groups of factors are considered as contributing to the decline in numbers after ploughing. Direct observation showed that many wireworms were destroyed in the actual process of cultivation. Evidence was insufficient to prove that the physical condition of cultivated soil adversely affects the number of wireworms. Comparison of the smaller size‐groups in pasture and in the cultivated fields showed that the wireworm population failed to replenish itself under arable conditions.
THE INSECTICIDAL ACTION OF SOME D.D.T. ANALOGUES AND CHLORINATED (4‐CHLOROPHENYL)‐ETHANES
Authors: STRINGER A. 
Published: February 2008

The insecticidal effectiveness of D.D.T. is dependent upon the combination of the two chlorophenyl groups with the trichloroethane group. Modification of the latter group results in a loss of toxicity. The toxicity of the compounds possessing =CH.CC13, =CH.CHC12 and =CH.CH2C1 groups decreases as the degree of chlorination decreases.None of the chlorinated (4‐Chlorophenyl)‐ethane compounds are of the same order of toxicity as D.D.T. The relative potency increases with increasing chlorine content of the side‐chain, although complete chlorination results in a compound possessing negligible toxicity. A relationship between toxicity and chlorine content is also seen in the ethylenic compounds, which were formed as intermediates in the synthesis of the ethane derivatives. The comparatively non‐toxic ethylenic derivatives of D.D.T. when contrasted with (4‐CIC6H4) CC1=CC12, suggests that the spatial configuration of the molecule may be of importance.
THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS III. COMPETITION WITH AGROSTIS GIGANTEA
Authors: MANN HAROLD H. , BARNES T. W. 
Published: February 2008

The twitch grass Agrostis gigantea var. dispar occurs commonly as a serious weed on the light semi‐acid soils found on the lower greensand near Woburn, Beds. It spreads rapidly by means of rhizomes, rarely forming stolons. All the rhizome growth takes place within 6 in. of the surface: I g. dry weight of roots and rhizomes may occupy up to 260 C.C. of soil. A. gigantea is slightly more easily eradicated than Holcus mollis.When barley and this Agrostis are planted together, with abundance of water and nutrients for both, it is found that increasing the density of planting of the barley reduces the crop loss due to Agrostis competition, but the weed can, nevertheless, diminish the yield of close‐planted barley by about a quarter. In a sparse crop of barley, any increase in Agrostis growth is reflected in an almost equal reduction in yield of barley. In proportion to its relative density the barley secures a larger share of the soil nitrogen than does the Agrostis.Evidence is given suggesting that there is a marked effect of the one grass on the other even when there is no competition for root space and an ample supply of water and nutrients.
THE MOVEMENT OF TOBACCO MOSAIC VIRUSES AND POTATO VIRUS X THROUGH TOMATO PLANTS
Authors: Capook S. P. 
Published: February 2008

Tomato aucuba mosaic virus, tobacco mosaic virus and potato virus X took 3'5‐4, 5 and 3 days respectively to move from inoculated tomato leaflets into the petioles and stemsOn reaching the stem each virus usually first moved downward, but in some plants both upward and downward movement occurred simultaneously and in a fewupward movement occurred first.All three viruses travelled through the stem at approximately the same rate. Each was capable of travelling more than 80 cm. during the first 12 hr. after entering the stem, giving a minimal average rate of about 8 cm. per hr.Uninfected pieces of stem invariably occurred between infected pieces. Maximum lengths of stem through which virus particles had apparently passed without causing infection, were 44.5, 49 and 39 cm. for the three viruses.
OBSERVATIONS ON APPLE CANKER III. THE ANATOMY OF THE STEM CANKER
Authors: CROWDY S. H. 
Published: February 2008

The development of cankers caused by Nectria galligena on apple is described; the pathogen exploits all the tissues outside the xylem and will also penetrate the xylem to an appreciable depth, invading the xylem parenchyma, vessels and fibres.Spread in the peripheral tissues is checked to some extent by successive barriers laid down by wound phellogens, but the barriers are eventually passed by the mycelium. There appear to be two distinct ways in which these barriers are passed: there may be direct penetration which appears to be associated with an aggregation of the mycelium into blocks, and symptoms suggestive of mechanical rupture; or there is an alternative route in which the pathogen grows in the lumen of the fibres and emerges behind the barrier.In the xylem the spread of the pathogen is checked by tyloses and gumming in the vessels, and by gumming in the parenchymatous tissues, but in the fibres there appears to be no defence mechanism, and the spread beyond the gum barriers was usually recorded in the xylem fibres. It is suggested that the presence of the pathogen in the xylem fibres might provide the explanation of the formation of cankers on partially healed pruning cuts, and this type of canker is described in some detail.The development of the canker depends on the balance between the development of the pathogen and the resistance of the host, and there is some discussion on the relation of this balance to the control of the disease.
OVERWINTERING OF APHIDS, ESPECIALLY MYZUS PERSICAE (SULZER), IN ROOT CLAMPS
Authors: BROADBENT L. , CORNFORD C. E. , HULL R. , TINSLEY T. W. 
Published: February 2008

Mangold clamps in many districts of the British Isles were found to provide overwintering sites for Myzus persicae (Sulz.), Hyperomyzns staphyleae (Koch) and Aulacorthum solani (Kalt.). After a severe winter, when other means of overwintering are few, clamps may be the most important source of Myzus persicae. Only Myzus ascalonicus Doncaster was found in swede clamps.Factors affecting the infestation of clamped mangolds by M. persicae were the number of aphids on the crop when lifted, the methods of topping and clamping the roots, and the temperature in the clamp. M. persicae was introduced on the leaves, and close topping was often an efficient means of control. Close topping did not control Hyperomyzus staphyleae; normally, this aphid does not seem to be a root‐feeding species, but with artificially colonized mangolds it fed on both exposed roots and foliage. It is not known how this species enters the clamps. The temperature in clamps was influenced by that of the outside air and the type of cover, but changes were long‐term and did not reflect diurnal variations in external air temperature. Straw, covered with soil, was the best form of cover.In addition to harbouring Myzus persicae, mangold clamps are also important sources of sugar‐beet yellows virus.