Eco-physiological studies on desert plants : VII. Water relations ofLeptadenia pyrotechnica (Forsk.) Decne. growing in the Egyptian Desert.

1. Leptadenia pyrotechnica (Forsk.) Decne. grows in valleys of the Eastern Desert in Egypt where the climatic and edaphic drought is very severe. 2. The transpiration rate is low in winter months and rises by the onset of summer. The rise in transpiration rate is not comparable with that of the evaporation. 3. The maximum transpiration rate is generally attained earlier than the maximum of the evaporating factors, specially in summer. The transpiration curves show a rapid decrease after this maximum despite the continuous rise of the evaporating power of the atmosphere. This points to an effective stomatal regulation. 4. The osmotic pressure ofLeptadenia is relatively low. The osmotic pressure values show narrow daily and seasonal fluctuations. 5. Leptadenia pyrotechnica is one of the most drought resistant plants. Its xeromorphic leafless habit implies reduction in the transpiring surface, while its deep extensive roots and low transpiration rate ensure a favourable water balance. The mechanisms of drought resistance in this plant were discussed.