Hi Mark, Water within the cells of the leaves expands as if freezes, ice crystal form within the cell walls, and thus the cell walls swell and are less able to support the weight above them. This happens at ground level first because the air there is colder and denser. Best Wishes, Dave David Fenwick The African Garden 96 Wasdale Gardens Estover Plymouth Devon England PL6 8TW 01752 301402 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com/). Version: 6.0.544 / Virus Database: 338 - Release Date: 25/11/03