摘要:

In sand‐culture experiments with carrots, it was shown that a moderate quantity only of nitrogen was necessary for optimum growth compared with, for example, the turnip root. A moderate amount of (available) phosphorus was also sufficient for this purpose, as with the turnip, but contrary to experience with lettuce roots and tops. The greatest concentration of potassium applied, however, was probably the best for root development. Deficiency of phosphorus caused bronzing of the leaves, and absence of potassium, serious scorch; absence of boron resulted in a small, immature plant. Initial field trials on an old river gravel during experiments throughout the last 7 years indicated that dung gave no advantage over artificials, that artificials were possibly not needed on dunged land or land in good heart, and that land out of good heart, undunged and unfertilized throughout the 7 years, responded well to artificials, particularly phosphate and potash. The incidence of carrot fly, according to preliminary experiments, seemed to depend greatly on the nutrition of the carrot

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06148.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06149.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

Experiments carried out during the carry months of four consecutive years lead to the following conclusions: (1) high soil moisture accentuates the pre‐emergence damping‐off of peas; (2) a useful measure of disease control is obtained by dressing the seed with red cuprous oxide or an organic mercurial preparation. The addition of a sticker is undesirable with both fungicides; (3) whereas cuprous oxide has, more often than not, exceeded the mercurial preparation in giving increased emergence, the latter has the advantage of reducing the amount of seed‐borne (Ascochyta) disease. In addition, the danger of an overdose is less with the mercurial preparation than with cuprous oxide; (4) the presence of a growth‐promoting substance in a mercurial preparation gave no increased beneficial effect, as regards emergence, vigour of growth, or reduced liability to phytoddal

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06150.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

Experiments on the transmission of the ‘stripe’ disease of the narcissus are described. It was found that the disease is not seed transmitted but that it is transmissible by grafting and by juice inoculation with the use of an abrasive such as carborundum powder. Under field conditions transmission of the disease takes place above ground and not through the roots. The identity of the vector has not been established. The effect of the disease in reducing bulb growth and vigour has been examined. Controlling the spread of the disease by roguing is recommen

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06151.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

The results of a survey of aphis populations on potatoes in Devon and Cornwall; with special reference toMyzus persicae Sulz., during the years 1937‐41 are given. One or more counts were made by the standard method at 107 centres to determine population index figures. The results are summarized in the form of a map. The highest index figure obtained during the 5 years was 609, and only on six other occasions was the figure of 100 exceeded; of these centres only one was situated in the area considered to be especially favourable to seed production, and this centre was a market garden. The distribution of the various species of potato aphides is discussed, together with their fluctuations from year to year; special reference is made toM. persicaeandM. ornatus.Observations on the parasitism ofM. persicaeare described. The relationship of the proximity of winter hosts, altitude and of meteorological conditions, to the populations ofM. persicaeis discussed. The conditions for the production of seed potatoes in Devon and Cornwall are summarized. An account is given of those areas in Devon and Cornwall deemed suitable for seed production. A short account of the formation of a ‘Seed Potato Growers' Association’ in Devon and Cornwall has been

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06152.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

Pyrethrin, the active principle of pyrethrum powder, is insoluble in water but is soluble in, the body fluid of the cockroach. It has a selective action on nerve ganglia, and the destruction of their cells is responsible for the death of the insect. Whereas pyrethrum, when used ‐either in the powdered form or in a fluid state mixed with kerosene and introduced directly into the body cavity reaches the ganglion with the circulation, its mode of action when it acts through the spiracles is different. Kerosene‐pyrethrum mixture when introduced into the tracheal trunks through the spiracles is quickly diffused into the haemocoele. When the dry powder is inserted into the trachea, its mode of action is analogous to a fluid preparation. As the conversion of pyrethrum from a dry into a fluid state is alone possible in the interior of the trachea, the natural conclusion is that a fluid analogous to the body fluid is present in the same situation. As soon as the pyrethrin is dissolved, it is quickly diffused into the haemocoele and thus reaches the nearest gangl

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06153.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

An assessment of the numbers of flies emerging from a bacteria bed has been almost continuous through nearly 8 years, and an attempt is made to explain the reasons for the specific fluctuations. These are found to depend on weather influences reacting onMetriocnemus longitarsusand the wormLumbricillus lineatus, two forms which dominate the upper, region of the bed, the former being potentially predaceous.The annual cycles ofM. longitarsusare so timed that there is a major flight in May establishing its offspring in June. If June is cold and wet this form is successful and a barrage of larvae is formed in which much oviposition of the other species takes place. The eggs are largely destroyed in the barrage. Hot dry Junes are unfavourable to establishment and the barrage is thinned, or it may be dispersed by subsequent dry conditions.M. hirticollishas a major flight about a month later and so is dependent for summer establishment on a dearth or dispersal ofM. longitarsuslarvae. Spaniotoma minima is similarly affected, but the effect is less lasting because its cycles are rapid and it has the capacity for recovery in the cooler months which leads to a reasonable flight in May. The thermal requirements ofM. hirticollisdo not allow of this except in a very mild winter, and consequently it cannot recover from collapse until a season recurs in which hot dry conditions cause failure or dispersal of the barrage. The distribution of weather was such that gradations with a 4‐year interval were set up in the annual incidence of these flies.When the larvae ofS. minima(and possibly, but not distinctively, those ofM. hirticollis) are reduced by abundance ofM. longitarsuslarvae, pressure in the depths of the bed is relieved of a proportion of forms also potentially predaceous. By this thepsychodids, which probably always oviposit to some extent in the depths, are benefited and are able to extend their seasons of abundance later in the year than usual.The numbers ofS. minimaandM. hirticollisemerging in the early part of the year are largely determined by their autumn abundance, so the fluctuations of the whole year are referable to interspecific competition regulated by summer weather. This is not so for the other common flies which are markedly influenced by events in winter as well as in summer. There is a tendency forPsychoda alternatato be more abundant after a warm winter because its physiological requirements are a paramount factor, but some evidence is found that extra pressure of the other larvae may reduce it then as they do later in the year. Conversely the numbers ofM. longitarsus, and still more ofP. seoerini, tend to be less after a warm winter in spite of the fact that they are essentially winter‐breeding insects. This is attributed to the intervention ofL. lineatusin competition because the worms breeds mainly in the winter months and its thermal requirements are such that a rise from 7 to 10d̀ C. (about the limits of cold and warm in the beds in winter) causes a great acceleration in its cycle, while cold conditions drive it down from the surfacePhormidiumwhich it almost completely destroys in spring. Therefore it is suggested that the time of sloughing will be earlier or later in spring according to the winter‐bed temperature. This hastens or retards the period of deprivation for the larvae and so regulates distinctively the prosperity of the flies which breed briskly in winter and early spring. As assessments ofL. lineatuswere not made throughout the period these findings are theoretical. It is thus shown that the annual fluctuations of these forms are partly dependent on weather conditions and partly dependent on interspecific competition regulated by the weather. In several cases competition is shown to be the more potent direct inf

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06154.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

Compared withLumbricillus lineatusthe cocoons ofEnchytraeus albidusare smaller and contain fewer eggs whilst the egg production per worm is higher and sterility among the eggs lower. The fecundity ofE. albidusis greater over a temperature range 1–25d̀ and is not so adversely affected at the higher or lower temperatures asL. lineatus.Incubation inE. albidusis longer than inL. lineatusbut the time required for maturation is much shorter, the periods depending upon the temperature. There is a similar relation to temperature as in the case of fecundity, withE. albidusagain more tolerant to heat and cold. There is no relation between size and temperature but unlikeL. lineatus, growth occurs after maturation inE. albidusand its cocoons (after the first) and their egg content are larger. There is no apparent relation between the setae length and temperature. The temperature relations favour a more rapid increase ofE. albidusin the bacteria beds than ofL. lineatusbut they are well suited to the distribution of the species under natural conditions,E. albidusfavouring a terrestrial habitat whereasL. lineatusexists in moister places. Further, they show specific physiological differences distinguishing the two species of wor

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06155.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

The potato varieties Epicure and Doon Star permitted the production of fewer and smaller cysts ofHeterodera schachtiion their roots than the varieties Golden Wonder and Majestic, when all were grown under standard conditions. Under the stimulus of potato‐root excretion the number of larvae which emerged from Epicure and Doon Star cysts was less than that from Majestic or Golden Wonder cysts of the same volume. Accepting Lapage's (1938) criteria of resistance to nematode infestation in animals and applying them to plants, it is concluded that this deleterious effect of the variety on the eelworm is probably of the nature of a degree of resistance to eelworm attack specific to each variety and is physiological and not anatomical in action. Of the varieties tested, Epicure is judged the most resistant, closely followed by Doon Star. Majestic is fairly susceptible but not so much so as Golden Wonder on which the eelworm forms large cysts that are extremely productive of larva

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06156.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

Experiments on the biological measurement of toxicities, and others requiring the use of the probit transformation in the statistical analysis, have in die past been largely of a unifactorial nature. In order to reach a fuller understanding of the action of insecticides and other poisons it is necessary that experiments be performed in‐which two or more factors relating to the dosage are subjected to variation. Bliss has recently described methods for the analysis of two‐factor experiments, but his technique is not a direct extension of the simple case for the fitting of a probit regression line, nor will it generalize easily when more factors are involved.In the present paper it is shown that probit regression planes and hyper‐planes can be fitted in a way exactly analogous to that used for the regression line. Tests of heterogeneity and of parallelism, and standard errors of parameters are readily derived. The notion of relative potency of two poisons does not extend so easily, and it is suggested that the mean probit difference should be used in its stead as a measure of their relative effectiveness. As in the unifactorial analysis, the routine of fitting the. regression equations may be repeated until satisfactory accuracy in the estimation of the parameters is attained, but usually one, or at the most two, cycles of the process gives values sufficiently near to the maximum likelihood solution for practical purposes.A more general class of equations is introduced for use when the probit mortality is linearly related to each dosage factor separately, but the individual effects are not additive. The suggestion made by Bliss (1040) for this case lacks symmetry and does not completely fulfil the linearity conditions, but the present proposal avoids these defects and permits the making of tests for the significance of the im‐proval in fit effected by the additional parameters.The arithmetical procedure for the fitting of a probit plane is described in detail for data on the toxicity toTribolium castameionof a pyrethrin oil spray at various levels of concentration and deposit weight. Two methods of applying the poison were compared in this experiment, and the two series of results were excellently fitted by parallel probit planes. Direct spraying gave slightly, but not significantly, higher kills than the film method of application, and under the particular conditions obtaining, increasing the concentration of pyrethrin in the spray was a far more effective means of increasing kill than was a proportionate increase in the total amount of spray available to the insects. Numerical examples used by Bliss are also discussed in relation to die methods of fitting and forms of equation given in thi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1943.tb06157.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY