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Theodora Petanidou, , Erik Smets, The Effect of Nutrient and Water Availability on Nectar Secretion and Nectary Structure of the Dominant Labiatae Species of Phrygana, Systematics and Geography of Plants, Vol. 68, No. 1/2, Morphology, Anatomy and Systematics at the Centenary of Wilhelm Troll's Birth (1999), pp. 233-244
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Petanidou et al. (1999) studied this question.
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