ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05650.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05651.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

摘要:

Summary.1The food of aphids is the cell sap of plants, which they obtain by penetrating the tissues by means of a flexible, chitinous, piercing organ, which is composed of the maxillary stylets and the mandibles.2The maxillary stylets are closely apposed, thus forming two canals, which extend to the extremity of the compound stylet thus formed. The dorsal canal is the suction canal along which the plant juices are conducted into the pharynx. The ventral canal is the ejector salivary canal down which the saliva is pumped into the plant.3The penetration of the piercing organ is brought about by the retraction of the labium and the forward prolongation of the “forehead.” The labium at its distal end grips the piercing organ in a pincer‐like manner.4WithAphis rumicisthe piercing organ passes intercellularly through the cortex, only occasionally passing through individual cells. Eventually it reaches the vascular bundles.5The saliva is able to dissolve a passage for the piercing organ through the walls of the cells. It is also able to convert starch into sugar.6A well marked sheath, the stylet sheath, is formed round the piercing organ when it is in the plant tissues, its wall being composed of substances produced by the reaction of the saliva on the cell sap. It probably consists of callose and insoluble calcium pectate together with a deposition of tannin.7The saliva causes plasmolysis of the cells and disorganisation of the cell contents.8WithAphis rumicison beans, the phloem elements of the vascular bundles are the chief source of the food supply, although other cells of the plant, such as the cortex and mesophyll of the leaf may be tapped for nourishment, especially when the plant is heavily infested. Frequently inRumex,xylem vessels are tapped for food.9The presence of a thick cuticle may prevent young aphids from piercing into the tissues and inhibit a general infestation of the plant.10The sucking out process is usually intracellular, although intercellular suction sometimes occurs in the loose cortical tissue.11In the case ofMacrosiphumon the rose, occasional cells react under the influence of the saliva, resulting in a cellulose thickening of the cell wall of affected cells.12The varying constitution and concentration of cell Bap in different plants is an important consideration in respect to the biology and physiology of aphids.13The more favourable development and reproduction of aphids on certain plants is probably associated with the nature of the cell sap, and an investigation of the cell sap of plants under varying cultural conditions and manurial treatment appears to be necessary.14The composition of the excrement of aphids, or honey dew, depends upon the species of plant and aphid concerned, and is in close relationship with the composition of the cell sap of the plant and the digestive processes of the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05652.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05653.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

摘要:

SUMMARY OF PARTS I AND II.1Common Scab consists of a number of types of scab, which vary considerably in general appearance. Of these, the two most marked types have been called “Raised and “Pitted respectively. Other types are intermediate between these extremes. The causal organism in all cases examined belongs to the Actinomyces genus. The different strains isolated exhibit considerable differences in culture but, for the present, they may be placed in a single Actinomyces scabies group.2The incidence of scab is closely associated with soil type. It occurs most commonly and with greatest virulence on light, sandy or gravelly soils, especially on those of a “hungry nature. Conversely, it is rarely found on peat soils.3The diseaae may be inhibited by the applieation of sufficiently liberal dressings of green‐manure to the soil. Spent hops have also proved to be of value in this respect and leaf mould has long been used by gardeners with good results.4The action of lime or chalk on scab production depends largely upon the initial reaction of the soil. On neutral soils, it exerts little or no effect. On distinctly acid soils, it tends to produce or aggravate the disease unless the soil contains a large reserve of vegetable organic matter. This effect may be counteracted by green‐manuring.5The hydrogen‐ion concentration of the soil is not the direct factorof control in the occurrence of scab and this statement is borne out by the following facts:(a). Scab is found to only a slight extent in soils of a high hydrogen‐ ion concentration, yet, it may occur and Actinomyces have been found in large numbers in soils with a pH value as low as 4.4.(b). In more nearly neutral soils, there is no relation between the hydrogen‐ion exponent of the soil and the occurrence of scab. Thus, for example, one soil having a pH value of 7.0 may yield absolutely clean crops, whilst another with the same exponent may produce very scabby crops. Thia distinction cannot be explained by supposing the former soil to be virgin and uncontaminated with scab organisms.(c). In the treatment of scab by green‐manuring, any change brought about in the soil reaction appears to be towards a decrease rather than an increase in the hydrogen‐ion concentration.66. The established facts concerning the common occurrence of scab on light soils, its comparative absence on peat soils, the action of lime and the cure of the disease by green‐manuring may be explained by the Preferential food hypothesis. According to this theory, the scab organisms are primarily saprophytic living on vegetable remains in the soil. They remain 80 until their natural food supply is exhausted and develop their parasitic tendenciee only under the stress of hunger.77. Scab is more prevalent in dry than in wet seasons. This is no doubt due in some small degree to the higher soil temperature obtaining in dry seasons. The climatic factor of greatest importance, however, would seem to be rainfall which modifies the air content of the soil and thus regulates the development of the scab organisms which are strongly aerobic. The effect is most marked in clay soils where scab is almost entirel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05654.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

摘要:

Summary.The organism which produces “Stripe” disease of the tomato is shown to be the cause of a number of “Streak” diseases of other plants, namely sweet pea, culinary pea, broad bean, french bean, red clover, lucerne, lupin, vetch, sainfoin and

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05655.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

摘要:

Summary.1The sequence of events during the healing of the cut surface of a potato tubei is carefully traced.Apart from unessential colour changes, the first process in the healing of the tuber is the deposit of a fatty “suberin” layer, formed by the oxidation and condensation of fatty substances depositing from the sap drying up in the tissues at the cut surface.2The condition essential to the formation of this layer is access of oxygen.3If the cut surface is exposed in a moist atmosphere the layer is continuous; in a dry atmosphere, especially in sunlight, the layer may not be continuous.4This layer forms within 24 to 48 hours. A few days later cork is formed below this suberin deposit as the result of cell divisions in an actively dividing layer, the cork phellogen.5The essential factors promoting the activity of this phellogen appear to be the accumulation behind the blocked surface of sap containing substances diffusing from the vascular bundles, and the production of an acid reaction just below the blocked surface by the anaerobic conversion of sugars into fatty acids.6The activity of the cork phellogen may be roughly estimated by the numbeT of layers of cork produced. Comparative data are presented for a number of varieties of potato which show that Majestic, King Edward VII and Bishop are particularly deficient in this important activity connected with the healing of wounds.7The bearing of these facts as to the process of wound healing is considered in relation to the practice of propagation by potato sets and two practical conclusions drawn. (1) Potato tubers should not be cut in sunlight or left in too dry a place. (2) The practice of liming potato sets appears to be without justification so far as its use in promoting the healing of the wound is concer

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05656.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05657.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05658.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1923.tb05659.x

出版商:Blackwell Publishing Ltd    

年代:1923

数据来源: WILEY