Summary Weedy Orobanche and Phelipanche species are important in Southern and Eastern Europe, the Middle East and North Africa, and have recently been reported in the USA, Australia and some countries in South America. Rather than being controlled, the Orobanche and Phelipanche problem is increasing, both in intensity and in acreage. Large areas of new territory are at risk of invasion, if care is not immediately taken to limit the introduction of parasitic seeds and to educate farmers and others to be alert for new infestations. There is an urgent need to re‐evaluate novel integrated Orobanche and Phelipanche management programmes that will allow a better control of the parasite species and limit their distribution. The main obstacle in the long‐term management of Orobanche and Phelipanche infested fields is the durable seedbank, which may remain viable for decades in the field. Large quantities of long‐lived seeds give the parasite genetic adaptability to changes in host resistance and cultural practices. As long as the seedbank is not controlled, the need to control the parasite will persist whenever a susceptible host is grown in the infested field. We discuss strategies for seedbank reduction, paying particular attention to cultural practices, whereas chemical and biological control methods are covered by other reviews in this issue.

520 535 544 532 543 542The pigment of the blue cornflower, protocyanin, is a complex of high molecular weight. Iron(III) and aluminum ions combine with the anhydro base of the cyanin to form deep-blue complexes, which are stable in the physiological p H range. Complexes of this type also have been synthesized. Alkali iiretal salts play no part in blue flower pigments. Formation of blue complexes can be prevented by sequestration of the metal ions with stronger complexing agents, e.g. flavonols. The variuticn of flower colurs can be explained to a large extent on the basis of the complex formation of anthocyanins. In delphinidin glycosides, the color base or airhydro base is stable even in slightly acidic media.

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The effect of various phenols and aromatic amines on the dynamics of the peroxidase-catalyzed aerobic oxidation of NADH was investigated. We demonstrate that several aromatic compounds may substitute for 2,4-dichlorophenol in inducing sustained oscillations and complex dynamics in the reaction. These aromatic compounds can also act as substrates in the classical peroxidase reaction. Since some of the aromatic compounds studied are naturally occurring substrates for peroxidases, we conjecture that oscillations and complex dynamics may well occur in the intact plant.