Drosera whittakeri was grown in sand cultures supplemented with inorganic salt solutions lacking either nitrogen, sulphur, phosphorus or the microelements. Application of the insect Drosophila melanogaster to the tentacles of plants raised on nitrogen or sulphur deficient medium, enhanced growth, which on nitrogen deficient medium was accompanied by decreased nitrogen content per unit weight although the total nitrogen per plant was unaffected. Application of insects to plants on media deficient in phosphorus or the microelements had no effect on growth but significantly increased the phosphorus content of plants grown on a complete nutrient solution or media deficient in phosphorus or nitrogen. Insects would not serve as a heterotrophic carbon source for the realization of maximum growth of plants grown at very low light intensities.
Optimum growth of Drosera binata (and usually D. whittakeri) was attained by applying insects to plants raised on nitrogen-free medium; addition of inorganic nitrogen (as nitrate) to the nutrient solution to plants raised under these conditions inhibited growth. Optimum growth was not achieved by growing plants on a complete nutrient solution in the absence of insects.
Up to 50% of the phosphorus in the tubers of D. whittakeri occurred as inositol hexaphos-phate. Phosphorus was rapidly transferred to the growing parts of the plant on emergence. During the growing season, plants with higher than average phosphorus content developed new rhizomes on which new tubers formed. The indigenous distribution of Drosera species in southeastern Australia is not restricted to soils of very low phosphorus, nitrogen and sulphur status.