摘要:

SummaryThe effects of potato virusXupon the carbohydrate and total nitrogen contents of potato leaves have been followed over diurnal and seasonal periods in the varieties President and Arran Victory.The gross metabolism of carbohydrates has been found to be similar in both mosaic‐diseased and normal leaves.Three major trends of carbohydrate metabolism, each of which may be identified with a particular stage of leaf development, have been recognized and discussed.Slight modifications of the fundamental metabolism of diseased leaves have been found in a reduced photosynthetic activity, disturbed starch‐sugar relationships, and an impediment in translocation during the pre‐senescent stage. All these have been ascribed to secondary effects arising out of the pathological change brought about as a result of virus infection.Transient modifications in carbohydrate metabolism have been traced to prematurely retarded growth activities leading to a diminished demand for carbohydrate in support of growth in the diseased plants.A significantly greater content of nitrogen has been found in diseased leaves at all stages of growth, and it has been suggested that the pathological symptoms and prematurely retarded growth activities which give rise to disturbances in carbohydrate metabolism are direct manifestations of a disorganized nitrogen metab

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06981.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

Summary1The fungus causing apple canker is described and its identity withNectria galligenaBres. is confirmed.2The methods of dispersal of the spores ofNgalligenahave been examined. The ascospores are discharged forcibly from the perithecium, the eight spores of each ascus typically being ejected simultaneously.3Field investigations have shown that spores are discharged during wet periods at all times of the year. Ascospore discharge reaches its maximum in January‐February and falls to a minimum in the summer months.4The dispersal of conidia occurs during wet periods in the spring and autumn.5Germination both of ascospores and conidia occurs over a range of temperature from 2 to 30°C, the optimum being at 20

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06982.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

Summary1Inoculations withN. galligenaon unwounded shoots of apple show that canker infections through leaf scars may be initiated in October and April but not in November and January. Shoots sprayed before inoculation with a Bordeaux‐casein‐oil mixture gave a much lower proportion of infection than those unsprayed.2Inoculations withN. galligenaon pruning cuts showed that freshly made pruning cuts on apple shoots are susceptible to canker infection throughout the dormant season. Pruning cuts made during autumn and winter acquire a natural immunity to infection within 2 months.3Several wound sealing materials applied to pruning cuts failed to give protection from canker when the treated surfaces were inoculated withN. galligena.The most promising wound protectant tested was a mixture of monohydrated copper sulphate, hydrated lime and linseed

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06983.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

Summary1The present contribution, as part of a general study of pink rot of the potato, deals withPhytophthora erythrosepticaPethybr. in its relation to staling, light, acidity, moisture and temperature.2In natural media the fungus is not, or but very slightly, affected by its own staling products, but, in general, is intensely intolerant to the presence of other fungi and bacteria.3Ordinary daylight is not concerned in the growth or reproduction of the fungus.4Growth occurs over a widepH range (3·2 tocirca9·0–10·0); sexual reproduction occurs over this range except towards the limits of acidity and alkalinity; asexual reproduction was not investigated experimentally. It is considered that modification of the soil reaction, within practical limits, does not offer a means for control of the disease.5The moisture factor controls directly the incidence of the disease in contaminated soil—withlowmoisture infection is inhibited; withnormalmoisture infection occurs via the dead or moribund stolon through the “heel” of the tuber; with high moisture the tuber is infected directly in the region of an “eye”. Sporangia are only formed under aquatic conditions and it is considered probable that “eye” infection is brought about through the agency of zoospores.6The temperature limits of growth are 0–32°C. with an optimum at 25°C. Oospore production occurs only between the optimum and minimum growth temperatures (0–25°C), being inhibited above the growth optimum. Asexual reproduction seems to be similar

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06984.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

Summary1Experiments carried out during 1933‐8 with the object of investigating the control of skin spot (Oospora pustulansOwen&Wakef.) by seed‐tuber disinfection are described.2Compounds of mercury were effective when used in solution as steeps. Formalin and a proprietary dusting compound proved to be non‐effective. Proprietary organo‐mercury compounds gave the most promising results, and were satisfactory when used as “instantaneous” dips (0·5‐1·0 min.); mercuric chloride solution was efficient but the 90 min. dipping period employed made the method too tedious.3The time at which the treatment is carried out is of great importance in determining the measure of control obtained. Disinfection of the seed at the time of digging was far more effective than immediately before planting. If too long an interval (more than 8 weeks) is allowed to elapse between digging and disinfection, the value of the treatment is substantially reduced.4A study of the time of digging the crop upon the incidence of the disease, made during one year only, indicated that for that year early digging did not reduce the amount of the disease which developed during subsequent storage. Disinfection carried out at each of the five diggings gave satisfactory control in each case.5The method of treatment recommended is the same as that previously suggested for the control of common scab (Actinomyces scabies(Thaxt.) Güss.) and blight (Phytophthora infestans(Mont.) de Bary). Some evidence was obtained of its also being effective against storage diseases. It would, therefore, appear that disinfection of seed tubers at the time of digging may prove effective against a group of tuber diseases many of which are transmissible to th

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06985.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

SummaryA study has been made of the sequence of fungi developing on wheat straw buried in four arable soils, an allotment soil, and a glasshouse compost. Both natural untreated straw, and straw autoclaved in a 2 % solution of sodium nitrate were employed.Fusarium culmorumandMucorspp. appeared to be dominant organisms in the earlier stages of straw colonization, but these were replaced byPenicilliumspp. in the latter stages of decomposition. The nitrogenous treatment of the straw favoured the development ofPenicilliumspp. at the expense ofFusarium culmorumandMucorspp. The pathogenicity of theFusarium culmorumisolates to wheat seedlings was established by inoculation experiments.The data provided by this investigation are considered sufficient to justify the inclusion ofF. culmorumin Reinking&Manns' (1933) group ofsoil‐inhabiting Fusaria, or true soil fung

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06986.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06987.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

Summary1Two types of apparatus for exposing insects to known concentrations of toxic gases, under controlled conditions, were constructed and are described.2The relative resistance of different stages of the flour beetle,Tribolium confusumDuv., to hydrogen cyanide was determined, the results being treated by Bliss's method. The order of resistance was pupa (most resistant), adult, larva, egg. The difference in resistance at different ages was found for the pupa, adult and egg. The application to all these results of Cotton's theory of the relation of rate of metabolism and susceptibility to fumigants is discussed. It is considered that this theory might hold for stages other than the egg.3A series of experiments was carried out to discover whether individual resistance to hydrogen cyanide was inherited. It was found that the offspring of resistant individuals were significantly more resistant than the offspring of susceptible individuals, and that this difference was maintained over several generations.4A considerable increase in resistance was found to occur if adult beetles were removed from their flour about an hour, instead of immediately, prior to their fumigation. The reason for this increase was not determined, but various suggestions to account for it are discussed.5It was noted that under certain conditions, adult beetles emitted a volatile substance which was self‐toxic, and also appeared to react with cyanide.6The dosage‐mortality curves for all the experiments are discussed and possible reasons for their apparent abnormality put forward.7The experiments here described, which must only be regarded as preliminary, emphasizei. The complexity of the problems arising in the study of the resistance of living organisms to toxic substances.ii. The need for carrying out such experiments under as natural conditions as possible.iii. The importance of a careful analysis of factors which affect the resistance of the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06988.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

Summary1A series of experiments was carried out upon the etiology of pea sickness, a disease which is invariably associated withHeterodera schachtii.2In addition to this eelworm, a fungus,Aphanomyces euteiches, was found to be concerned in the production of the diseased condition of the plants in the soil studied.3BothHeterodera schachtiiandAphanomyces euteichescan singly produce a pathological condition of the host in the absence of any other pathogenic factor.4The effects upon the plants of attack byHeterodera schachtiialone indicate that it is the primary cause of pea sickness.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06989.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY

摘要:

SummaryA quantitative analysis of the toxicity of drugs or poisons applied jointly requires that they be administered at several dosages in mixtures containing fixed proportions of the ingredients. From a study of the dosage‐mortality curves for several such mixtures, preferably in comparison with equivalent curves for the isolated active ingredients, most cases of combined action can be classified into one of three types:(1) The first type is that in which the constituents act independently and diversely, so that the toxicity of any combination can be predicted from that of the isolated components and from the association of susceptibilities to the two components. The coefficient of association can be measured experimentally and should be constant at all proportions of the ingredients. When high, the toxicity of the mixture is reduced. The form of the dosage‐mortality curve has been examined for several hypothetical mixtures. Whenever the curves for the two constituents were assumed to differ in slope, there was a relatively abrupt bend in the curve for the mixture, the rectilinear segments above and below the break approaching in slope the values for the original constituents. This observation indicates that in homogeneous populations the slope of a dosage‐mortality curve is of toxicological significance. Since the same numerical relations would be expected if a single poison were to have two independent lethal effects within the animal, there is theoretical basis for fitting the linear segments of a dosage‐mortality curve separately when a break occurs after transformation to probits and logarithms. This argument has been extended to time‐mortality experiments to explain the smoothly concave curves characteristic of natural mortality.(2) The second type of joint action is that in which the constituents act independently but similarly, so that one ingredient can be substituted at a constant ratio for any proportion of a second without altering the toxicity of the mixture. With homogeneous populations, dosage‐mortality curves for the separate ingredients and for all mixtures should be parallel. Although by hypothesis the susceptibility to one ingredient is completely correlated with that to the other, mixtures in this category are more toxic than in the preceding class where association may vary from 0 to 1. The numerical relations have been illustrated by an experiment on the toxicity to the house‐fly of solutions containing pyrethrin and rotenone. A mixture with a little less than four equitoxic units of pyrethrin to one of rotenone agreed closely with the definition but one in which the ingredients were about equally balanced showed a significantly greater toxicity than expected on the hypothesis of independent action, indicating the presence of synergism.(3) Synergism forms the third type of joint action, characterized by a toxicity greater than that predicted from studies on the isolated constituents. It is the reverse of antagonism, which has not been considered directly. Two methods are proposed for the analysis of synergism. The more direct is to relate equitoxic dosages of mixture to its percentage composition in terms of the more active ingredient. When both are in logarithms the relation is linear over a useful range of compositions. This procedure preserves the original structure of the experiment, can be extended readily to three or more ingredients and leads to a convenient practical result. Theoretically it is less satisfactory than a second method in which for equitoxic dosages of each mixture the content of one ingredient (A) is related to the content of the other (B.) The equation which satisfies this relation most completely is (1 +k1A)Bi=k2, where the three constants are computed from the experimental data. When the exponentiis equal to 1, only two constants need be determined and their product,k1k2, is proposed as a measure of the intensity of synergism.The synergism between a nitro‐phenol and petroleum oil has been computed by both methods. For mixtures containing from 0·5 to 5% of the nitrophenol, the deposit of mixture (Dc) killing 98 % of the eggs of a plant bug could be expressed adequately in terms of the percentage of the phenol (Q) as logDc= 0·687‐0·307 logQ, for 98% of overwintering San Jose scale as logDc= 0·472 ‐0·363 logQ.All observations, including those for a 0·1 % mixture and for oil alone which were omitted in the first method, could be fitted satisfactorily in terms of the separate ingredients. For plant bug eggs at LD50, (1+25·6A)B= 4·29 and for San Jose scale (1 + 66·7A)B= 2·73: in both casesi= 1 and the intensity of synergism 110 and 182 respectively.The full procedure has also been applied to the constituents of seven samples of Derris root. One sample gave an unaccountably low toxicity and was omitted. The log LD 50 of ether extract for the remaining six was related to the percentage composition of two components in the extract, rotenone (A) and dehydro mixture (B.) Since the toxicity of extract could be expressed almost entirely in terms of these particular two constituents, they were then related to each other by the second method. None of the samples contained a very small proportion of one ingredient, so that several equations were equally applicable, one of them being (1+0–714A)B= 56·1, from which the intensity of synergism was 40.The problem of measuring synergism in fumi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1939.tb06990.x

出版商:Blackwell Publishing Ltd    

年代:1939

数据来源: WILEY