Browsing by Author "Nutman, F.J."
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Item Agave Fibres. I. Morphology, Histology, Length and fineness; Grading Problems(1936) Nutman, F.J.; East African Agricultural Research Station, Amani, Tanganyika TerritoryThe paper is in the nature of a progress report on the work done on agaves as fibre producing plants at Amani during the last few years. Agave fibres are of 3 fairly well-defined types: - Mechanical, most strongly developed round the periphery of the leaf; these fibres are of great importance commercially; owing to their shape they seldom divide during manufacture and on their fineness depends the fineness of the sample. Ribbon fibres occur always in association with the conducting tissues though they are present in various sizes in all parts of the leaf except the extreme periphery; they form the longest fibres in the leaf and are important in that they split longitudinally, unlike the mechanical fibres, and therefore their original size does not influence fineness. Xylem fibres are of no commercial importance, being broken up and lost during decortication. Short leaves, whether caused by early cutting or environment, do not produce a markedly finer fibre than long leaves. Fineness of fibre is varietal, in which respect A. amaniensis and A. cantala are much superior to A. sisalana. A. amaniensis possesses a larger amount of short fibres than A. sisalana, but this is offset by the greater length of its leaves. The proportion of mechanical to ribbon fibre in A. amaniensis is twice as great as in A. sisalana. This fact is of technical importance, giving the fibres a different intrinsic make-up and probably affecting spinning behaviour. Methods of mechanical grading to replace the present grading by eye are thoroughly discussed and the defects of the present system pointed out. Nevertheless, expensive grading schemes cannot be put into operation until the consumer gives some indication of the type of fibre required, and so far, this has not been forthcoming.Item A Convenient Method for the Excavation of Growing Trees in Undisturbed Soil(1940) Schmid, F.A.F.; Nutman, F.J.; East African Agricultural Research Station, Amani,It is often desirable to use, as experimental material, a plant grown in the open under normal field conditions and subsequently dug up and potted. This is particularly true of slow-growing bushes and trees, for the establishment of seedlings in large containers may take years, and the filling of soil into such receptacles invariably result in a substrate dissimilar to undisturbed soil. In horticultural practice, the removal of large plants to new sites with the minimum of disturbance to growth is necessary in many instances.Item An Inexpensive Recording Manometer(1937) Nutman, F.J.The publication by Gregory and Pearse of the technique for measuring stomatal movements by means of the recording porometer has marked a not inconsiderable advance in parameter. Not the least advantage of the method is that stomata movements are recorded as such on a chart, and need no further working out, as is necessary with the more widely used Knight parameter. The method of recording used in the latter, though automatic, necessitates measurement of the recorded time-intervals, and the tedious plotting of these.Item Investigations on A Disease of Coffea Arabica Caused By A Form of' Colletotrichum Coffeanum Noack.(1961) Roberts, F.M.; Nutman, F.J.By the use of certain techniques, the inoculum production by different portions of the bearing wood of coffee trees can be determined. Conidia from infected fruit were found to play only a minor part in the spread of coffee berry disease; conidial production from bearing wood is responsible for the level of disease in any season. The region of maximum crop density on the bearing wood coincides with that of maximum inoculum production. Control measures directed not at protecting the developing fruit, but at reducing the amount of inoculum produced by the branches, give satisfactory results. The importance of this in relation to control measures, and to the geographical spread of the disease, is discussed.Item The Length of Sisal Fibres with particular reference to Grading Problems(1935/1936) Nutman, F.J.The producers of sisal fibre are now taking great interest in the grading of their product. The arguments in favour of grading are familiar to everybody, and I need not recapitulate them here. My purpose is to summarize some of the data which have been accumulating at Amanien the variation in length of sisal fibre: in the light of this knowledge to discuss whether gra dm"g" IS practl"Ca-b.1e , an r..1 , "If so, to suggest the most suitable characteristic of the fibre tembody in a grade definition.Item Method of Uredospore Dispersal of the Coffee Leaf-Rust Fungus, Hemilela Vastatrix(1960) Roberts, F.M.; Nutman, F.J.; Bock, K.R.Experimental evidence is presented against the view that uredospores of the rust, Hemileia vastatrix, are normally distributed by wind, although this method of dispersal does apparently occur at a very low level. The uredospores of the rust adhere strongly to each other, to leaves, and to any surfaces however smooth. Their mutual adhesion is broken down by water, and it is concluded that the periodic build-up of rust epidemics is almost entirely a result of sporedispersal by water-splash. This observation has an important bearing on the problem of control.Item A Note on a Laboratory Technique for Testing(1970) Nutman, F.J.; Roberts, F.M.Many attempts have been made to evaluate fungicides in the laboratory for their possible use against coffee berry disease. For example during the period 1957-58, the writers (unpublished data) carried out a series of screening tests with over 20 fungicides, using as criteria the depression of mycelia growth rate: the reduction in germination on both agar films and on berry surfaces; the reduction in formation of appressoria; and the reduction in lesion production on berries, all over a wide range of concentrations of the fungicides used. At the same time Bock (1963) was evaluating the field performance of some of these in an extensive series of comparative field trials.Item A Note on a Laboratory Technique for Testing Fungicides against Coffee Berry Disease(1979) Nutman, F.J.; Roberts, F.M.Many attempts have been made to evaluate fungicides in the laboratory for their possible use against coffee berry disease. For example, during period 1957-58, the writers (unpublished data) carried out a series of screening tests with over 20 fungicides, using as criteria the depression of mycelial growth rate; the reduction in germination on both agar films and on berry surfaces; the reduction in formation of appressoria; and the reduction in lesion production on berries, all over a wide range of concentrations of the fungicides used. At the same time Bock (1963) was evaluating the field performance of some of these in an extensive series of comparative field trials.Item A Note on a Possible Natural Inhibitor of Germination in Colletotrichum Coffeanum Noack(1970) Robert, F.M.; Nutman, F.J.A Parasitic Strain of Colletotrichum Cofjeanllm Noack, an Ubiquitous Saprophyte On Cofjea Arabica, Arose In Kenya Shortly Before 1922 (Macdonald, 1926). This Causes Lesions Bearing Acervuli on both Green and Ripe Berries. Acervuli Are Also Formed On the Surface Of The Maturing Wood of the Branches.Item The Root-System Of Coffea Arabica Pt. I. Root -Systems In Typical Soils Of British East Africa(1932) Nutman, F.J.THIS paper reports the results of an investigation of the root-system of coffee, carried out during 1932. It forms part of a pro gramme for the detailed investigation of the physiology and anatomy of the coffee tree, as laid down at the Amani Conference in 1931 [1]. Estates have been selected which represent the greater part of the areas under cultivated arabica coffee in Tanganyika, and at the same time show as wide a range of soil variation as possible. In addition, two areas in Kenya have been included for purposes of comparison. The data presented here are the results of field study only, and consequently the conclusions drawn from them must necessarily await experimental confirmation. In spite of this, it is thought advisable to publish this separate account of the field studies, since the subject has possible practical applications, and the necessary experimental work will be lengthy.Item Some Mechanical Characters of Agave Fibres(1942) Nutman, F.J.; East African Agricultural Research Station, Amani,The fibers of various species of Agave, mainly of A. sisalana, have until recently been used for little but the making of binder twine. For this they are suitable both in strength and in other characters. There has therefore been but little incentive to detailed study of the fiber.Item Stimulation of Two Pathogenic Fungi by High Dilutions of Fungicides(1962) Roberts, F.M.; Nutman, F.J.At very high dilutions, a wide range of fungicidal chemicals stimulates conidial germination, growth, and infectivity of the pathogenic form of Colletotrichum coffeanum Noack. Stimulation of germination is independent of nutrition; its degree is dependent on viability, the relation being logarithmic and identical with that between viability and nutrition. Germination of the uredospores of Hemileia uastatrix Berk. & Br. is also stimulated by fungicides at high dilution; again the degree of stimulation is greatest with spores of low viability. It is suggested that the physiological mechanism leading to stimulation may be the same for all fungicidal substances.Item Studies of the Clove Tree I. Sudden-Death Disease and its Epidemiology(1949) Nutman, F.J.; Sheffield, F.M.L; Clove Research Scheme.Sudden-death disease of cloves has been present and steadily increasing in both Zanzibar and Pemba for many years. The only premonitory symptom is a slight chlorosis followed by thinning of the foliage and reduction of the absorbing system. Death follows after a period, which may vary from only a few days to many months. Death occurs from lack of water caused by the disorganization of the absorbing roots......Item Studies of the Physiology of Coffea Arabica(1937) Nutman, F.J.In a previous communication (Nutman, 1937) examples have been given of the daily march of assimilation of Coffea Arabica leaves in the field, showing that there is a marked midday drop in assimilation rates when the leaves are exposed to direct sunlight, but not when they are shaded, nor during cloudy weather. It was concluded that this drop in assimilation was not due to the water relations of the leaf or of the plant as a whole, nor to an excessive accumulation of assimilates in the leaf, nor to a solarization effect. It was suggested that stomatal changes might explain the observed phenomena" and, if so, stomatal aperture should be directly correlated with light at low intensities inversely correlated at high intensities.Item Studies of the Physiology of Coffea Arabica(1941) AMANI; Nutman, F.J.When Balls (1937) described a method of weighing by the use of an automatic chain balance! a valuable instrument was made available to the plant physiologist. It has always been recognized that the weighing of rooted plants grown in sealed containers is the only sound method for determining transpiration rates. But, especially where large plants are used, the weight of the plant and its container is very great compared with the weight-changes to be measured, and large balances are seldom sensitive. Consequently measurement of weight-loss over short time-intervals has been impossible.Item Studies of the Physiology of Coffea arabica III. Transpiration Rates of Whole Trees in Relation to Natural(1941) Nutman, F.J.; East African Agricultural Research Station, Amani, TanganyikaWHEN Balls (1937) described a method of weighing by the use of an automatic chain balance! a valuable instrument was made available to the plant physiologist. It has always been recognized that the weighing of rooted plants grown in sealed containers is the only sound method for determining transpiration rates. But especially where large plants are used, the weight of the plant and its container is very great compared with the weight-changes to be measured, and large balances are seldom sensitive. Consequently, measurement of weight-loss over short time-intervals has been impossible.Item Studies of the Physiology of Coffea Arabica III. Transpiration Rates Whole Trees in Relation to Natural Environmental Conditions(1941) Nutman, F.J.WHEN automatic Balls chain (1937) balance1 described a valuable a method instrument of weighing was by made the use available of an automatic chain balance1 a valuable instrument was made available to the plant physiologist. It has always been recognized that the weighing of rooted plants grown in sealed containers is the only sound method for determining transpiration rates. But, especially where large plants are used, the weight of the plant and its container is very great compared with the weight-changes to be measured, and large balances are seldom sensitive. Consequently measurement of weight-loss over short time-intervals has been impossible. Balls claimed that his method enables weighing to be made on a steelyard with an accuracy approaching that of a good chemical balance, and quotes data illustrating an accuracy of 1: 3 50,000. I have used a modification of his method and have found that his claims can readily be confirmed and are in fact conservative. Thus it becomes possible to record the march of the transpiration rate of large plants over very short time-intervals, and the relation between the march of transpiration rates and the varying meteorological factors can be studied in a way hitherto impossible.Item Studies of the Physiology of Coffea arabica: III. Transpiration Rates of Whole Trees in Relation to Natural Environmental Conditions(1941) Nutman, F.J.; East African Agricultural Research Station, AmaniWhen automatic Balls chain (1937) balance1 described a valuable a method instrument of weighing was by made the use available of an automatic chain balance1 a valuable instrument was made available to the plant physiologist. It has always been recognized that the weighing of rooted plants grown in sealed containers is the only sound method for determining transpiration rates. But, especially where large plants are used, the weight of the plant and its container is very great compared with the weight-changes to be measured, and large balances are seldom sensitive. Consequently measurement of weight-loss over short time-intervals has been impossible. Balls claimed that his method enables weighings to be made on a steelyard with an accuracy approaching that of a good chemical balance, and quotes data illustrating an accuracy of 1: 3 50,000. I have used a modification of his method and have found that his claims can readily be confirmed and are in fact conservative. Thus it becomes possible to record the march of the transpiration rate of large plants over very short time-intervals, and the relation between the march of transpiration rates and the varying meteorological factors can be studied in a way hitherto impossible.Item Studies of the Physiology of CoHea Arabica I. Photosynthesis of Coffee Leaves under Natural Conditions(1937) Nutman, F.J.I N certain of the coffee-growing areas of East Africa a serious trouble known as 'overbearing and die-back' occurs. This has been described (Nutman, 1933) and evidence presented for the view that the heavy demands for carbohydrate by the developing crop exhaust the reserves, and exceed the normal daily carbon income of the tree. The branches then die back; the greater part of the feeding roots is lost and not regenerated; and the tree is permanently injured. Although it may not die for several years it remains unproductive.Item Studies on the Biology of Hemileia Vastatrix Berk. & BR.(1963) Roberts, F.M.; Nutman, F.J.Germination of the uredospores of Hemileia vaslatrix can occur ' only in the presence of liquid water, either in the dark or in light of low intensity the latter stimulating the onset of germination at low, but not at optimal temperatures. On agar the optimum is 22C., the minimum I5°c and the maximum 28'5°. On leaf surfaces, however, germination is markedly depressed at ca. 24°, resulting in a bimodal relation with temperature. After subjection to moderately low temperatures a marked stimulation of termination follows on transference to the optimum, the amount of the stimulus being proportional to the duration of the exposure to the lower temperature. Spores of H. vaslalrix: cannot infect except at comparatively high concentrations, hence the threshold period for successful infection is longer than the time necessary for the formation of appressoria by individual spores. Lesions can occasionally develop after 3 1/2 hr. exposure to conditions which permit germination, but the number increases with the length of exposure up to at least 12 hr. Germination is more frequent on young leaves than on old, and at the margins than near the mid-rib. When stored dry the spores are relatively short-lived, losing 50 % of their viability in less than 2 days. \When wetted for very short periods and then dried for equally short ones, their germinative capacity is very greatly reduced. The relation of these findings to conditions in the field is discussed.
