SUMMARYExperiments were carried out, during three years , on a population oi Asphodelus aestivus Brot. (Liliaceae) in a semi-arid environment, to test whether seed production of plants was limited by quantity and/or quality of pollen supply. The natural pollinators are mainly solitary bees.The fraction of flowers setting fruits varied from 8 to 40 % between years. Fruit set of plants caged to exclude insects was less than 3%. Fruit set was increased by artificial pollination of flowers with their own pollen to 43-64%. This indicates that the plant is self-compatible, but due to the position of the anthers and stigma, insect visits are required for effective pollination. Cross-pollinated caged flowers set yet more fruits (59-82 °o) and much more (2-4 times) full seeds per fruit than self-pollinated flowers.The artificial addition of cross-pollen to flowers, in the natural environment, increased the mean number of full seeds per flower on the whole plant. Thus, natural reproduction was limited by insect pollination.A quantitative effect was indicated by a strong positive association between the number of pollen grams on a stigma and the probabilities of the flower maturing a fruit and of its ovules setting seeds. Furthermore, in 20-60 % of flowers in the population, stigma loads were less than 13 pollen grains, which indicated very low probability of fruit maturation.A qualitative response was shown by the positive effect of artificially added cross-pollen on the number of full vs. empty seeds, an effect similar to that of cross-vs. self-pollination in caged plants.The proportion of full seeds developing in a clone of Asphodelus m the natural population was inversely related to the proportion of inflorescences in its neighbourhood that belonged to the same clone, which suggests that fertility is limited by an excess of pollen from the same clone being supplied by insects.It is concluded that female reproductive success of Asphodelus aestivus in its natural environment depended on both the amount and origin of the pollen supplied by its pollinators.

Levulinic acid, an inhibitor of porphyrin biosynthesis, causes marked accumulation of a low molecular weight polypeptide in greening maize (Zea mays L.) leaves. Additional compounds which interfere with porphyrin synthesis (e.g. aminooxyacetate, iron-chelators, 4,6-dioxoheptanoic acid) had a similar effect. The polypeptide accumulated in the cytosol and could not be detected in the plastid stroma. Its molecular weight was estimated as 4800 daltons by electrophoresis in sodium dodecyl sulfateacrylamide gels containing urea and glycerol.

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