- Summary 1 We investigated the genotypic effects of selection by herbivory by the dorcas gazelle, Gazella dorcas Linnaeus 1758, on the production of calcium oxalate crystals in the lily Pancratium sickenbergeri C. et Barbey in the Negev Desert. 2A completely crossed experimental design was used to assess the effects of soil calcium concentration and herbivory (simulated by clipping) on the production of calcium oxalate crystals in the leaves of plants from four source populations with different levels of herbivory. 3 Soil calcium concentration did not have significant effects on the production of calcium oxalate crystals in the leaf. The number of crystals did not increase significantly with the clipping treatments. 4 There was no significant difference among plants germinated from seed from populations with high or low herbivory in the production of calcium oxalate. 5 There was a trade-off between investment in defence versus investment in growth, suggesting a cost to defence. Experimentally clipped plants grew more than unclipped plants. Families from high-herbivory areas had a stronger regrowth capacity in the absence of herbivory. 6Our results indicate that crystal production by these plants is not a sink for excess calcium uptake from the soil. We conclude that in this species calcium oxalate crystal production is for defence, and that this defence is constitutive rather than inducible. The environmental unpredictability in this desert leaves plants with few cues to the onset of herbivory. Constitutive defence may be a more appropriate strategy than inducible defence in this environment, particularly when herbivory is high, and leaves are ephemeral.