摘要:

Summary.In mature plant materials pentosans form the most important food for micro‐organisms.The Klober and Tollens method for the determination of pentosans is not specific for these compounds.While pentosans are easily attacked by micro‐organisms, the other furfurol‐yielding compounds are found to be resistant, and it is therefore essential to get a correct figure for pentosans. A possible method is suggested: to determine the furfuroids in the cellulose obtained by the chlorination method and to deduct this amount from the total furfuroids.Two factors appear to control the decomposition of ripe cellulosic materials in the presence of assimilable nitrogen. The one is the food, or, better termed,energy factorwhich is the pentosans, the other is the physical orinhibitory factorwhich is the lignin. It is found that if the ratio of energy factor to inhibitory factor is above 1, the material is easily decomposed; but if it is below 0.5, the material is very resistant to microbial attack. The prediction of the “decomposability” of a material is thus possible.Attempts to increase this ratio in resistant materials by the addition of carbohydrates proved unsuccessful. It was concluded that since micro‐organisms obtained their food materials outside the tissues, they did not attack the tissues until the more easily available food‐stuffs were exhausted. Thus the decomposition of the material was actually less than was possible under natural conditions.Mannose and galactose do not appear to form suitable food for the micro‐organisms concerned in these processes and it is concluded that the pentosan part of the hemi‐celluloses is most important as microbial food.The study of the relative importance of bacteria and fungi proves that under the conditions of these experiments, fungi play a more prominent part especially during the early stages of such decomposition.The study on the availability of the nitrogen of the fungal bodies proves it to be of the resistant type. It seems that at later stages of decomposition under natural conditions fungi are decomposed by other organisms.The ability of certain fungi isolated from such decomposing heaps, to grow at high temperature as well as on purified carbon constituents of plants, and also the presence of almost all the enzymes necessary to hydrolyse the complex carbon constituents, further confirm their importance. The possibility of their activity under natural conditions in manure heaps is s

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07004.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY

摘要:

Summary.1Under controlled conditions in water cultures soluble silicate was found to have little effect upon the growth of barley if phosphorus were also present, but if the latter were absent a significant increase in dry weight was induced by the silicate.2The addition of silicate caused an appreciable increase in the height of the main shoot, which was most marked in phosphate‐free solutions, becoming less evident as the quantity of phosphate present was increased.3Leaf development was retarded by phosphate deficiency and hastened by the addition of silicate.4A close association exists between the amount of phosphate present, and the effect of silicate upon the rate of tillering and the number of tillers developed.5Soil cultures with barley and mustard in pots with various forms of silicate showed that soluble silicates are more active than glass silicates, tending to cause increase in dry weight with deficient mineral manuring, and in some cases also with complete manuring.6Further soil experiments revealed variations in the response of barley and mustard to silicate on different types of soil. A general improvement occurred with increasing doses of silicate together with various combinations of manures, notably when phosphorus or potash was deficient.7The significance of the results obtained has been examined statistically, and an attempt made to formulate the effect of added silicate in terms of an increase in the efficiency of the superphosphate presen

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07005.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY

摘要:

Summary.Summarising the results of the experiments described in the present paper, it is evident that bunt has a distinct influence on vegetative organs of the plant in addition to the well‐known effect on the grain. Both species which cause bunt,Tilletia triticiandT. laevis, were included in one experiment only, from which it appears that the influence of the latter species, while tending hi the same direction, was distinctly weaker in its effect thanT. tritici. This conclusion is in harmony with the results of other workers (4,10, 11).The following conclusions refer toT. tritici, with which speck the work was mainly carried out:1Soil germination and establishment.The actual percentage of germination has not been found. to differ appreciably in bunt‐free and bunt‐contaminated samples, but in one experiment a considerable difference was manifest in the final establishment, the bunt‐free samples showing an increase of 25–37 per cent, when compared with those which were contaminated with spores before sowing (Table I). The greatest difference (37 per cent.) was shown by the variety Browick, which gave the lowest establishment figure and had presumably suffered most intensely from the unfavourable climatic conditions.2Early growth.The first visible symptoms of a retarding influence on growth are not always manifest at the same stage of development in the wheat plant. Under one set of conditions (p. 92) the effect was clearly shown by plants in the seedling stage, since those derived from bunt‐contaminated seed differed from the control by 14–17 per cent. in height, and 16–20 per cent. in the dry weight of 100 shoots. In another experiment (p. 97) where a considerable reduction in height was evident at maturity the plants showed no appreciable effect during the first ten weeks of growth.3Tillering.In the matter of tillering the influence of the fungus was in the opposite direction to that recorded for growth in height, bunted plants at the period of maximum tiller development producing in one experiment 16 per cent. more tillers than healthy plants grown under precisely the same conditions. At maturity in both cases the number of heads was considerably less than the total number of tillers produced, but bunted plants still showed an increase over those that were healthy (Experiments III and IV).A similar difference was noted in the case of plants grown in rows in the field1.4Length of straw at maturity.A reduction in the length of straw appears to be one of the most constant results of the influence of the fungus on vegetative growth. It will no doubt be shown that the degree of reduction varies with the variety, the season and possibly with the origin of the spores used for contamination. In the experiments here described a reduction in height amounting to 16–19 per cent. in the case of Hen Gymro and 13 per cent, in the case of April Bearded was recorded. It was shown moreover that the reduction was considerably greater in the case of tillers carrying heads in which every grain was bunted than in the case of those bearing both healthy and bunted grain.5Length of ripe ear.In the case of Hen Gymro wheat the fungus showed a slight retards effect on the length of the ear, while in the variety April Bearded the bunted ears were, if anything, slightly longer than the normal. More data are desirable on this point, since the influence on this organ is probably largely determined by the morphology of the ear in any particular variety. It appears to be generally recognised that ears of thecompactumtype are abnormally narrow and long when bearing bunted grain (6,15). Plate VII shows bunted and normal ears ofT. vulgarevar. Standard Red, which possesses normally relatively wide, dense ears. For comparison are shown healthy and diseased heads of Hen Gymro, which has ears characteristically lax.6Root development.In one experiment where data were obtained on the dry weight per 100 plants of the roots at maturity a significant difference was apparent between bunted and healthy specimens, the former showing a decrease of 22 per cent.From the practical point of view, where the final yield of healthy grain is of primary consideration, the most important aspect of the question, apart from the effect on the grain itself, is probably the influence of the disease on establishment and early growth. It is of come recognised that any check which the plant receives in the early stages of growth will be exaggerated later in the case of plants placed in competition with healthy individuals, as must happen in a partially bunted field crop. The full extent of the retarding influence on growth was possibly not exhibited in certain of the experiments under review since the bunted plants were not seriously subject to competition.Since it has been shown that the presence of the parasite tends to increase tillering, the reduction in heads at harvest which was a striking feature of previous treatment experiments must be attributed either to the stimulating effect of the chemical used for treated lots, or to the depressing influence of bunt on establishment in the field. From the data here given the second alternative seems the more feasible, but since the Muence of bunt on establishment is, perhaps more than any other, reply to be affected by seasonal conditions and to differ with the variety and the origin of the seed, it is desirable to obtain further data on this of the problem, using a large number of seed samples and varieties and a wide range of environ

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07006.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY

摘要:

Summary.In the season 1925–6 an interesting relationship was noticed between yellow rust of wheat,Puccinia glumarumand bunt or stinking smut of wheat,Tilltia tritici;it was observed that:1Bunted Little Joss wheat plants were badly rusted and that plants free from bunt were free or comparatively free from rust.2Bunted plants of other wheat varieties were definitely more rusted than plants free from bunt.3It is suggested that rust resistance which cannot be broken down artificially may be broken down by natural contamination of wheat with the bunt fungu

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07007.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY

摘要:

Summary.1An account is given of some preliminary experiments with insects as transmitters of potato mosaic disease. The various types of insect‐proof cage which have been used in these experiments are described.2The following insects were used in the inoculations:Aphididae.Myzus persicae.Macrosiphum gei(=solanifolii).Myzus Circumflexus.Aleurodes, White‐fly.Asterochition vaporariorum.Capsidae.Calocoris bipunctatus.Lygus pabulinus.Typhlocybidae, Leaf‐hoppers.Zygina pallidifrons.Eupteryx auratus.3The aim of the experiments is definitely to identify what insects of those normally attacking the potato are disseminators of virus disease.4Infected insects were placed both upon the sprouts of tubers and upon the haulm; the latter is the only satisfactory method for insects other than aphides.5Successful transmission of mosaic disease was obtained in 1925 by means of the aphidesMyzus persicaeandMacrosiphum gei. Some evidence of infection by means ofAslerochiton vaporariorum(greenhouse white‐fly) and the leaf‐hoppersZygina pallidifronsandEupteryx auratuswars also obtained; further work with these insects is required before definite conclusions are drawn. The capsid bugsLygus pabulinusandCalocoris bipunctatwfailed entirely to transmit th

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07008.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY

摘要:

Summary.This paper is a contribution to our very scanty knowledge of the BritishHarmolita, a phytophagous genus of the superfamily Chalcidoidea (Hymenoptera). Many species of this genus are pests on cereals and cultivated grasses; one species,Harmlita tritici, is the notorious joint‐worm of America and Russia, whilst species attacking many other cereals and grasses have been recorded in Europe and America. An account is here given for the first time of the life history and biology of a British species ofHarmolita, namelyHarmolita graminicola, which is a gall former on couch grass (Triticum repens).The larva of another undetermined species ofHarmolita, also gallicolous onTriticum repensis figured and briefly described.The adult ofHarmolita graminicolabegins to emerge in the last week of June and continues to appear during the first week of July. When the inflorescence has appeared through the sheathing leaves the female fly will not lay eggs on them. One egg is deposited on each culm just beneath the rudimentary inflorescence, the ovipositor of the fly piercing the sheathing leaves in order to reach the desired position. TheHarmolitaeof both species were bred in captivity and the length of the period of incubation of the egg was found to be between three and four weeks. Experiments were conducted to ascertain whether parthenogenesis occurred in this species. The results were negative although perhaps not numerous enough to be conclusive.The larva possesses four instars and moults three times whilst feeding, another moult occurring at pupation. The larval instars can be differentiated most exactly by the state of development of the sub‐apical tooth on the mandible. The sub‐apical tooth is absent from the mandibles of the first instar; only incipiently developed in the second instar; better developed in the third and fully formed in the fourth instar. The larva becomes full fed in October and hibernation takes place in the larval stage. Pupation begins to occur near the end of April but the great majority pupate in the middle of May.There is a short semi‐pupal stage of from 12 to 24 hours duration immediately before the pupal moult takes place. The pupal stage lasts about 40 days and there is only one generation each year. The larva ofBracon erythrostictus(Lyle) was found to be parasitic onHarmolitain the latter's larval stages; no other insect parasites were found. BothHarmolita graminicola(Gir) and the undetermined species refused to breed on wheat or any other plants of theTriticumgenus although many attempts were made to induce them t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07009.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY

摘要:

Book reviewed in this article:The Theory of the Gene. By ThomasHuntMorganLife of Plants. By Sir FrederickKeebleContributions from the Harvard Institute for Tropical Biology and Medicine, III, 1926Plant Nutrition and Crop Production. By E. J. RussellCitrus Diseases and their Control. By H. C. Fawcettand H. A. Lee

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1927.tb07010.x

出版商:Blackwell Publishing Ltd    

年代:1927

数据来源: WILEY