4 simple formula has been adopted to determine a figure that might be regarded as the expected additive effect of two chemicals, i.e., by taking the percentage weed control achieved by the bipyridyl alone and applying this to the percentage uncontrolled by the residual alone. The sum of this and the response obtained by the residual may be regarded as the expected additive effect. The responses obtained by the three residual herbicides are broadly similar and means of these have been treated in this manner for simplicity. The expected additive effect figures are shown in parentheses in Table 111. This adequately demonstrates the value to be obtained in weed control over a whole growing season by applying mixtures of bipyridyls and residual weed killers. This applies particularly in the case of paraquat and the result is far greater than the initial advantage obtained by the rapid action of the bipyridyls.Paraquat is undoubtedly the most effective material in this r61e and examination of the results shows that each of the residuals has benefited outstandingly from its addition. This may be due in part to its effect upon grasses, including many perennial grasses, and its greater translocation capacity than that of diquat.These mixtures of bipyridyls and residual weed killers are interesting and much work remains to be done to utilise them to maximum effect and usage.
ConclusionOne main conclusion can be drawn from these trials, that is, that in the field of total weed control one is working on the problem of selectivity no less than in the field of selective crop protection. The discovery of the substituted ureas and triazines has indeed revolutionised total weed control but the problem of selectivity remains. Until a herbicide is found which is, at once, effective as a post-emergence application for deep-rooted perennial plants, and also as a pre-emergence application with, preferably, the capacity to destroy the ungerminated seed, mixtures of herbicides for total weed control are still required.Changes in t h e composition of tomato fruit during ripening have been studied with particular reference t o titratable acidity, sugars and soluble solids. The analyses were made on juices expressctl from whole fruit, and also on free juices from the locules.The content of sugars and of total solids in juices from whole fruit, and of sugars in the locular juices, increased from t h e niatui-e grecn t o t h e orange-red or red stages of ripening.The acidity of t h e juices decreased progrcssivcly as orange and red pigments developed in the outer walls, the highest values in the locules gencrally occurring in the rnaturc green fruit mhercas for whole fruit a maximum was found at t h c first appearance of yellow areas in the malls.Storage of orange-red tomatoes at room temperature for 6 days caused a significant decrease in sugars and titratable acidity in the expressed juices.* P a r t I1 :
IntroductionIn previous studies of the composition of normal, ' blotchy ' and ' waxy ' tomatoesl> 2 the results were based on analyses o...
Comparison of normally ripened tomato fruit and fruit showing uneven pigmentation has revealed considerable differences in composition. Thus the normal fruit had a significantly higher content of dry matter, and higher concentrations of total solids, reducing sugars and nitrogenous compounds were found in sap expressed from normal than from blotchy fruit. Sap from normal fruit also had the higher titratable acidity and lower pH.
A comparative study has been made of some components of the green and red areas of the walls of ‘blotchy’ tomatoes. The juices expressed from the green areas showed a significantly lower titratable acidity than those from the red areas, and had a lower content of sugars and nitrogenous compounds. Juices from the green areas also contained less soluble solids, as determined by oven‐drying, and had lower refractive indices.
The content of ethanol‐soluble total sugars and free and total acids was significantly lower in the green than in the red areas. The proportion of alcohol‐insoluble solids was higher in the green areas.
The results are discussed in relation to the changes in composition previously found during ripening. Some aspects of the results suggest that ‘blotchy’ cannot merely be attributed to delayed ripening in the affected areas.
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