Message: 10 Date: Wed, 14 Nov 2007 07:22:44 -0800 (PST) From: Robt R Pries <rpries@sbcglobal.net> Subject: Re: [pbs] Old Wives, water droplets was FROST To: Pacific Bulb Society <pbs@lists.ibiblio.org> Message-ID: <795313.49011.qm@web81915.mail.mud.yahoo.com> Content-Type: text/plain; charset=iso-8859-1 I some of the posts there was speculation about water droplets focussing sumlight and causing damage. As I remember the old wives tales; their concern was about water droplets setting on leaves in the middle of the day in Spring or summer. I guess I need to verify that with my wife. I believe there was also a warning that water droplets should not set on leaves of African Violets if the sun is coming through the window. I sort of understand the last tale since African Violets (Santipaulia)growing in a window on a winters day may suffer chill damage from the rapid evaporation of a water droplet as the sun hits it. Sunlight is directly related to evaporation rates. This is how they discovered that less sunlight strikes the ground today then 50 years ago because evaporation rates have fallen. The sun is still puting out the same amount of light but the polution in the atmosphere now reflects as much as 20% back to space before it gets to the earth. I have wondered if this is having an effort on plants that require high light intensity for growth. But back to the water droplets. I don't remember any wives tales that talk about water droplets focusing light in winter. Robert: I always assumed that the water droplet, kept above the surface of the leaf by the leaf hairs of the saintpaulia, would then be able to act as a lens and focus light onto the leaf. Just like a magnifying glass. It doesn't really make sense, as I think about it, and I suspect you'll agree, that the sun's heat would lead to increased chilling of the leaf under where the waterdrop was located--it wouldn't evaporate any more rapidly than the sun's heat caused it to vaporize. Jonathan Knisely Coastal Connecticut, USDA 6a