摘要:

Summary1The relation between certain insects and the intracellular micro‐organisms they harbour is obscure and cannot be described as symbiotic for the following reasons:(a) Sterile mycetomes are known to occur in some species closely related to others with heavily infected mycetomes.(b) Defloration experiments have been carried out successfully without any harmful effect to the host insect.2Intracellular micro‐organisms in xylophagous insects cannot be considered as playing an important role in the digestion of wood for the following reasons:(a) In weevils with wood‐eating habits which have intracellular micro‐organisms, the latter only pass into the lumen of the gut of their host during the adult stage when the insect is not feeding on wood.(b) Some wood‐eating species of insects harbour intracellular micro‐organisms, while closely related species with similar feeding habits are free from these.(c) The intracellular micro‐organisms of some wood‐eating forms have been cultivatedin vitroand found to be unable to break down cellulose.3The relatively high content in nitrogenous substances of different kinds of wood, and the general occurrence of proteolytic enzymes in insects, make the assumption that intracellular micro‐organisms fix atmospheric nitrogen for the use of their host superfluous.4The extracellular intestinal micro‐organisms of certain lamellicorn larvae and of some termites play no role in breaking down cellulose for the use of their host. They are utilised as a direct food source. Such insects are therefore better referred to as micro‐organism‐feeders.5True wood‐eating insects derive the necessary carbohydrates from the wood they live on through the activity of their own enzymes. The enzyme complex in such insects has been found to vary from species to species.6The carbohydrate components of wood vary in quantity in different kinds of wood.7Some true wood‐eating forms depend upon starch and soluble sugars for their source of carbohydrates. Such insects have no cellulase and can consequently only live in kinds of wood comparatively rich in starch and sugars.8Other true wood‐eating forms secrete cellulase and are therefore able to live in kinds of wood comparatively poor in starch and soluble sugars.9The occurrence of hemicellulase has been demonstrated only in a very few cases and the value of the hemicelluloses as food for wood‐eating ins

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01252.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

摘要:

Summary.About 1840, the beginning of the era of scientific agricultural chemistry, many chemists believed that ammonia was the principal, if not the sole form in which nitrogen was taken up by all plants. This view was abandoned, and towards the end of last century it was generally believed that with the possible exception of the Leguminosae, the higher plants took up their nitrogen almost solely from nitrate. This belief was in large measure founded upon the results of excessive attention paid to the conditions of soil which was not bearing vegetation.The discovery that leguminous plants were able by the help of specific bacteria to utilise atmospheric nitrogen was not thought to extend to any of the other higher plants. Though widespread use had been made by practical farmers of leguminous plants in association with non‐legumes, the idea of commensalism between legumes and non‐legumes did not arise amongst agricultural scientists until the present century was well advanced. The acknowledged benefits attained through the growth of legumes were over long ascribed to nitrification of decayed roots resulting from some previous (not to a simultaneous) legume occupancy. This theory may have been correct for the conditions of sinqle crops on arable soils, but was inadequate to account for the comparative failure of grassland and mixed forage crops to respond profitably to fertilising with quickly acting mineral nitrogenous manure.The rde of nitrate in the soil is not clearly understood; nitrate is most likely an end‐product of micro‐organic decomposition of organic materials. Its presence is detectable in notable amounts, and most clearly, in the absence of plants. This does not necessarily imply, as it was once thought, that it is preferentially absorbed by plants; it is suggested that plants can absorb some of the less highly oxidised forms of nitrogen which are the precursors of nitrate. In other words, the finding of nitrates in considerable amounts in soil indicates that there has been a local surplus of nitrifiable nitrogen compounds which plant roots have been unable to reach and consequently to absorb. No single compound of nitrogen can be named as the primary component of the nitrogenous nutrition of plants.Evidence is presented that non‐leguminous plants can profitably utilise compounds of nitrogen built up by the symbiotic life of nodule bacteria within their proper leguminous host plants. Some insight into the nature of the transferred compounds has been gained, though the conditionsin vitrodo not admit of facile extension to natural conditions. The mode of transfer from legume to non‐legume is still obscure, but the existence of a transfer can be taken to be well established; it represents a stage in a double symbiosis of which the importance has not been fully appreciated. It is probable that in the nitrogenous nutrition of plants some factors are involved which are not yet formulated. These accessory factors may be found to derive ultimately from the animal, aided by activity of legume nodule bacteria in the soil.Assistance given by the Imperial Bureau of Soil Science, Harpenden, in permitting a consultation of their card index relating to cover crops, is gladly acknowledged; and thanks are also due to Mr B. Weston, Field Superintendent at Rothamsted, for giving the benefit of his experienced observation to

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01253.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01254.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01255.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01256.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1934.tb01257.x

出版商:Blackwell Publishing Ltd    

年代:1934

数据来源: WILEY