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Two cultivars each of spinach, lettuce, cabbage, squash, and cauliflowers, as well as one cultivar of parsley were grown in open fields. In addition, two cultivars each of squash, cucumber, and tomatoes were grown in polypropylene-covered greenhouses. The effects of cultivar and harvest date on the nitrate and nitrite content of the edible parts of these vegetables were studied. Harvest date was found to have a significant effect (P≤0.05) on the nitrate content of the open-field-grown spinach, cabbage, and squash, and the nitrite content of the open-field-grown spinach, lettuce, and cabbage. Late-harvested vegetables had the lowest nitrate levels, while the pattern of their nitrite content was irregular with respect to the dates that gave highest nitrite levels in each vegetable. Harvest date had no significant effect on either nitrate or nitrite content of the greenhouse-grown vegetables.

A fragile plant cover has developed during the last two decades along the shores of Lake Nasser, the largest impoundment of the River Nile. Development of this vegetation has been influenced by the prevailing environmental factors. The statistical methods (ordination and classification techniques) emphasise the groups of species and elucidate their distribution within the environmental gradients. The applied methods indicate that the distribution of the species is strongly related to the moisture gradient. Some of the soil parameters also contribute to the gradient. The geographical gradient in the distribution of the species is less pronounced.

A “correlated queue” is defined to be a queueing model in which the arrival pattern influences the service pattern or vice versa. A particular model of this nature is considered in this paper. It is such that the service time of a customer is directly proportional to the interval between his own arrival and that of his predecessor. The initial busy period, state and output processes are analyzed in detail. For completeness, a sketch is also given of the analysis of the waiting time process which forms the subject of another paper. The results are used in the analysis of the state and output processes.