摘要:

Lettuce grown in nutrient solution sometimes showed slight benefit on a dry‐weight basis from the addition of 0.1 p.p.m. Cr, Sr, Ti or V, while Zn was usually harmful. Addition of Mo at a similar concentration, however, exerted such a marked beneficial effect on both yield and appearance as to suggest that this element was essential for healthy growth. Confirmation of the response was not always obtained, and search was made for some factor which would account for the lack of uniformity in the results. Neither the season of the year, the variety, modifications in the nutrient solution, nor the addition of other trace elements appeared to be responsible, and further work is necessary for the elucidation of the proble

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06309.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

An account is given of observations made on the effects on seed production of the incidence of the browning phase of the disease of flax caused byPolyspora LiniLaff. The work was carried out during three seasons.Disinfection of seeds before sowing exercises an effect on the average weight of the well‐developed seeds harvested, and the results obtained show that the intensity of the attack of browning in crops is inversely correlated with the weight of 1000 well‐developed seeds. When poorly developed seeds are separated from the remainder at harvest, evidence obtained in one year suggests that the percentage number of such seeds may be directly related to the incidence of browning in the crop. It was found in each of two years that more of the poorly‐developed than of the well‐developed seeds were contaminated withP. Lini.Evidence available for one year suggests that the viability of well‐developed seeds is not related to the incidence of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06310.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

Using naturally contaminated seed it is shown that the incidence of the seedling, stem‐break and browning phases of attack byPolyspora LiniLaff. in flax crops is related to the contamination of the seed with the parasite, the relationship being closer at low or moderate than at high levels of seed contamination. Heavy attacks of the disease did not occur when the number of contaminated seeds was less than 5%. A similar relationship was found to exist between the contamination of seed withColletotrichum linicolaPethybr.&Laff. and the incidence of seedling blight in the crop

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06311.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

The behaviour of the carrot‐fly population in the soil during autumn and winter has been investigated in East Anglia over the three seasons 1943‐5. The results show that the pest overwinters in both the larval and pupal conditions, and that the proportion of the individuals in each stage varies from crop to crop and from season to season. Samples taken from a May (1943) sown plot showed that pupation, which was 452% complete in October, rose to 742% in March and was not complete until late April. From a June (1944) sown plot of carrots samples showed a rise in percentage pupation from 8‐6% in October to 935% in March, the process probably being complete by early April. The changes in proportion of the soil larvae, carrot larvae and puparia in both the May and June plots were followed and are shown graphically. The changes in the size groups of the soil larvae and in the carrot larvae were also traced. The immature larvae persist longer in the carrots than in the soil. The size composition of the larvae from the soil of the June (1944) plot was recorded over the period September to April and the results are given graphically. Samples taken in October 1945 contained highly organized puparia from which flies emerged in a few days. These flies (third generation) gave rise to progeny which overwintered in the larval condition. The population in December 1945, composed chiefly of second generation puparia and third generation larvae, was very similar to that occuring in the previous two years. Mortality in the overwintering carrot‐fly larvae and puparia varied considerably but was frequently heavy. The principal agencies concerned were an hymenopterous insect,Dacnusa gracilisNees., and fungus and bacterial diseases. Other insect parasites occasionally important wereLoxotropa tritomaThorns, andAleochara sparsaHeer. Nematode parasites were also r

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06312.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

A variety of substances has been tested by laboratory methods as insecticides against the bed‐bug and the body‐louse. The oil‐soluble samples were tested by the Potter tower method which gave the most accurate results. Certain liquids were tested by a simple dipping method, and solids insoluble in mineral oils were tested as aqueous solutions by the dipping method or as dusts.Various organic thiocyanates were found to show similar relative toxicity to the louse and bug, but the pyrethrins were much more toxic to the latter. D.D.T. was highly toxic to both and Gammexane even more insecticidal, especially to the louse.In the dipping tests, two types of toxic action were observed: an immediate physicochemical action and a delayed lethal action due to asphyxiation. Refined mineral oils kill lice by the latter method. Among the aqueous preparations, the emulsion of cresols known as Lysol was noteworthy for its ovicidal powers.Some experiments were made with extracts of delphinium seeds, the insecticidal powers of which were shown to reside in the alka

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06313.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

The paper describes experiments and observations on the damage done by mites to stored grain, and methods of assessing the damage. It is confirmed that mites cannot penetrate grains if the grain‐coat is intact; but usually less than 10% of the grains are so intact.In laboratory experiments, mites consumed up to 3% by weight of the grain before dying out; they were able to destroy the germ completely, but consumed very little of the remainder; the maximum rate of consumption observed over a 5‐week period was 0‐29% of grain weight per week; when added to grain at 75% relative humidity in the proportion of 1% by weight, mites consumed 1% of the grain in 27 days at 21d̀ C, or in 37 days at 10‐15d̀ C. Although mites consumed the grain more rapidly at higher temperatures or humidities, they survived longer at lower temperatures or humidities, and finally did more damage. Mites consumed wheat germ flakes more rapidly than grain, and finally reduced its weight by 74‐85%.A system of symbols to represent degrees of damage to grain by mites, assessed visually, is presented, and approximate values for the equivalent weight losses are given. The relationship between the product, no. of mites per 100 ex. grain × time in weeks, and the degree of damage to grain, was calculated from experimental data; the damage done per unit of this density × time product was 2‐2‐5 times higher at 25 than at 5‐9d̀ C, and about 1‐4 times higher at 70 than at 90% relative humidity. The mean density × time value corresponding to 1% loss of grain weight was 526,000 at 250 C, and 1,765,000 at 5‐9d̀ C.Data from granary investigations show the degree of damage associated with various levels of population density and grain moisture. In infested storages, the amount of embryo material destroyed ranged from less than 1% of the total (bulk grain) to about 15% (grain in bags).Mites may cause a rise in the temperature or moisture‐content of grain, or an increase in the growth of microorganisms; but there is no evidence to suggest that serious damage from these causes is likely except that dense in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06314.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

Physical and biological data are presented from an infestation byLaemophloeussp. (unidentified but very near toL. minutusOliv.) in bulk wheat contained in open‐topped silo bins. Much of the life history of this species is spent within the grains of wheat under the conditions of this infestation. It follows that the density of population of this species in whole wheat can be estimatedonly by breeding out or by determining the carbon dioxide output of the grain. Some larvae are free‐living for part of their lives. No regular relation has been found between the number of larvae free‐living at any time and the number of insects remaining within the grains. The proportion of the total population which is free‐living is least when the total population is greatest. There is some evidence that the grain contained a light infestation ofLaemophloeus, fairly evenly distributed, before it was loaded into the silo bin. It is supposed that this was the source of the infestation studied. Factors which might be responsible for the uneven development of the population are di

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06315.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

A sectional tubular steel sampler has been designed, with which samples of grain have regularly been obtained at 1 m. intervals to depths of 15 m. in normal grain. A new form of this sampler permits re‐closing of the sampling ports after filling, so that contamination of the samples can be avoided. Associated records of the grain temperatures and samples of the intergranular gases have been obtained at similar depths. Certain precautions to be observed in sampling from silo bins are emphasized. Observations are reviewed which show the extensive effects of granular segregation during movement. Material, such as extraneous seeds, holed grains, etc., segregates so that (a) it is delayed in the outfall whilst emptying bins, (b) it is more concentrated in the central column of the bin after filling, (c) in direct sampling it is scarcer in the first part of the sample to fall into the container, with the implication that the sample as whole is deficient in such material. Larger objects settle at the surface of the grain on a moving belt, whilst smaller ones sink between the grains. The consistency of the results suggests strong reasons for a reconsideration of the principles of sampling, either direct or indirect. Meanwhile, samples obtained by any one method are likely to prove fairly consistent inter s

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06316.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

A nozzle, P.I.L. No. AN2, has been designed for, and used successfully in, the biological assay of insecticides in a heavy oil solution. This new nozzle is easier to adjust and gave a standard deviation of deposit one‐seventh of that given by the nozzle described by Potter (1941

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06317.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY

摘要:

Sucrose syrup is less satisfactory than honey as a winter and spring food for bees: a mixture of approximately equal parts of honey and syrup is of almost the same value as honey alone.Feeding confined to early autumn induced the strongest spring development of colonies; syrup feeding in the spring may retard colony development, and food supplied at this time is apparently wasted. Feeding with syrup and pollen is advantageous only when a colony is lacking in stores of carbohydrate and protein.A total of four British Standard brood combs full of pollen provides sufficient protein for a colony on B.S. equipment from autumn until April: the best results were obtained by providing colonies on eleven B.S. combs, in early autumn, with 35‐40 lb. of honey, or honey and concentrated sucrose syrup, and four brood combs full of polle

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1946.tb06318.x

出版商:Blackwell Publishing Ltd    

年代:1946

数据来源: WILEY